@article{KrollKernKubinetal.2016, author = {Kroll, Thomas and Kern, Jan and Kubin, Markus and Ratner, Daniel and Gul, Sheraz and Fuller, Franklin D. and L{\"o}chel, Heike and Krzywinski, Jacek and Lutman, Alberto and Ding, Yuantao and Dakovski, Georgi L. and Moeller, Stefan and Turner, Joshua J. and Alonso-Mori, Roberto and Nordlund, Dennis L. and Rehanek, Jens and Weniger, Christian and Firsov, Alexander and Brzhezinskaya, Maria and Chatterjee, Ruchira and Lassalle-Kaiser, Benedikt and Sierra, Raymond G. and Laksmono, Hartawan and Hill, Ethan and Borovik, Andrew S. and Erko, Alexei and F{\"o}hlisch, Alexander and Mitzner, Rolf and Yachandra, Vittal K. and Yano, Junko and Wernet, Philippe and Bergmann, Uwe}, title = {X-ray absorption spectroscopy using a self-seeded soft X-ray free-electron laser}, series = {Optics express : the international electronic journal of optics}, volume = {24}, journal = {Optics express : the international electronic journal of optics}, publisher = {Optical Society of America}, address = {Washington}, issn = {1094-4087}, doi = {10.1364/OE.24.022469}, pages = {22469 -- 22480}, year = {2016}, abstract = {X-ray free electron lasers (XFELs) enable unprecedented new ways to study the electronic structure and dynamics of transition metal systems. L-edge absorption spectroscopy is a powerful technique for such studies and the feasibility of this method at XFELs for solutions and solids has been demonstrated. However, the required x-ray bandwidth is an order of magnitude narrower than that of self-amplified spontaneous emission (SASE), and additional monochromatization is needed. Here we compare L-edge x-ray absorption spectroscopy (XAS) of a prototypical transition metal system based on monochromatizing the SASE radiation of the linac coherent light source (LCLS) with a new technique based on self-seeding of LCLS. We demonstrate how L-edge XAS can be performed using the self-seeding scheme without the need of an additional beam line monochromator. We show how the spectral shape and pulse energy depend on the undulator setup and how this affects the x-ray spectroscopy measurements. (C) 2016 Optical Society of America}, language = {en} } @article{MitznerRehanekKernetal.2013, author = {Mitzner, Rolf and Rehanek, Jens and Kern, Jan and Gul, Sheraz and Hattne, Johan and Taguchi, Taketo and Alonso-Mori, Roberto and Tran, Rosalie and Weniger, Christian and Schr{\"o}der, Henning and Quevedo, Wilson and Laksmono, Hartawan and Sierra, Raymond G. and Han, Guangye and Lassalle-Kaiser, Benedikt and Koroidov, Sergey and Kubicek, Katharina and Schreck, Simon and Kunnus, Kristjan and Brzhezinskaya, Maria and Firsov, Alexander and Minitti, Michael P. and Turner, Joshua J. and M{\"o}ller, Stefan and Sauter, Nicholas K. and Bogan, Michael J. and Nordlund, Dennis and Schlotter, William F. and Messinger, Johannes and Borovik, Andrew S. and Techert, Simone and de Groot, Frank M. F. and F{\"o}hlisch, Alexander and Erko, Alexei and Bergmann, Uwe and Yachandra, Vittal K. and Wernet, Philippe and Yano, Junko}, title = {L-edge x-ray absorption spectroscopy of dilute systems relevant to metalloproteins using an X-ray free-electron laser}, series = {The journal of physical chemistry letters}, volume = {4}, journal = {The journal of physical chemistry letters}, number = {21}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/jz401837f}, pages = {3641 -- 3647}, year = {2013}, abstract = {L-edge spectroscopy of 3d transition metals provides important electronic structure information and has been used in many fields. However, the use of this method for studying dilute aqueous systems, such as metalloenzymes, has not been prevalent because of severe radiation damage and the lack of suitable detection systems. Here we present spectra from a dilute Mn aqueous solution using a high-transmission zone-plate spectrometer at the Linac Coherent Light Source (LCLS). The spectrometer has been optimized for discriminating the Mn L-edge signal from the overwhelming 0 K-edge background that arises from water and protein itself, and the ultrashort LCLS X-ray pulses can outrun X-ray induced damage. We show that the deviations of the partial-fluorescence yield-detected spectra from the true absorption can be well modeled using the state-dependence of the fluorescence yield, and discuss implications for the application of our concept to biological samples.}, language = {en} } @article{KunnusJosefssonSchrecketal.2017, author = {Kunnus, Kristjan and Josefsson, I. and Schreck, Simon Frederik and Quevedo, W. and Miedema, P. S. and Techert, S. and de Groot, F. M. F. and F{\"o}hlisch, Alexander and Odelius, M. and Wernet, Ph.}, title = {Quantifying covalent interactions with resonant inelastic soft X-ray scattering}, series = {Chemical physics letters}, volume = {669}, journal = {Chemical physics letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0009-2614}, doi = {10.1016/j.cplett.2016.12.046}, pages = {196 -- 201}, year = {2017}, abstract = {We analyze the effects of covalent interactions in Ni 2p3d resonant inelastic X-ray scattering (RIXS) spectra from aqueous Ni2+ ions and find that the relative RIXS intensities of ligand-to-metal charge-transfer final states with respect to the ligand-field final states reflect the covalent mixing between Ni 3d and water orbitals. Specifically, the experimental intensity ratio at the Ni L-3-edge allows to determine that the Ni 3d orbitals have on average 5.5\% of water character. We propose that 2p3d RIXS at the Ni L-3-edge can be utilized to quantify covalency in Ni complexes without the use of external references or simulations.}, language = {en} } @article{LeitnerJosefssonMazzaetal.2018, author = {Leitner, T. and Josefsson, Ida and Mazza, T. and Miedema, Piter S. and Schr{\"o}der, H. and Beye, Martin and Kunnus, Kristjan and Schreck, S. and D{\"u}sterer, Stefan and F{\"o}hlisch, Alexander and Meyer, M. and Odelius, Michael and Wernet, Philippe}, title = {Time-resolved electron spectroscopy for chemical analysis of photodissociation}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {149}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {4}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.5035149}, pages = {12}, year = {2018}, abstract = {The prototypical photoinduced dissociation of Fe(CO)(5) in the gas phase is used to test time-resolved x-ray photoelectron spectroscopy for studying photochemical reactions. Upon one-photon excitation at 266 nm, Fe(CO)(5) successively dissociates to Fe(CO)(4) and Fe(CO)(3) along a pathway where both fragments retain the singlet multiplicity of Fe(CO)(5). The x-ray free-electron laser FLASH is used to probe the reaction intermediates Fe(CO)(4) and Fe(CO)(3) with time-resolved valence and core-level photoelectron spectroscopy, and experimental results are interpreted with ab initio quantum chemical calculations. Changes in the valence photoelectron spectra are shown to reflect changes in the valenceorbital interactions upon Fe-CO dissociation, thereby validating fundamental theoretical concepts in Fe-CO bonding. Chemical shifts of CO 3 sigma inner-valence and Fe 3 sigma core-level binding energies are shown to correlate with changes in the coordination number of the Fe center. We interpret this with coordination-dependent charge localization and core-hole screening based on calculated changes in electron densities upon core-hole creation in the final ionic states. This extends the established capabilities of steady-state electron spectroscopy for chemical analysis to time-resolved investigations. It could also serve as a benchmark for howcharge and spin density changes in molecular dissociation and excited-state dynamics are expressed in valence and core-level photoelectron spectroscopy. Published by AIP Publishing.}, language = {en} } @misc{JayNorellKunnusetal.2018, author = {Jay, Raphael J. and Norell, Jesper and Kunnus, Kristjan and Lundberg, Marcus and Gaffney, Kelly and Wernet, Philippe and Odelius, Michael and F{\"o}hlisch, Alexander}, title = {Dynamcis of local charge densities and metal-ligand covalency in iron complexes from femtosecond resonant inelastic soft X-ray scattering}, series = {Abstracts of Papers of the American Chemical Society}, volume = {256}, journal = {Abstracts of Papers of the American Chemical Society}, publisher = {American Chemical Society}, address = {Washington}, issn = {0065-7727}, url = {http://nbn-resolving.de/urn:nbn:se:uu:diva-370051}, pages = {2}, year = {2018}, language = {en} } @article{BeyeOebergXinetal.2016, author = {Beye, Martin and {\"O}berg, Henrik and Xin, Hongliang and Dakovski, Georgi L. and F{\"o}hlisch, Alexander and Gladh, Jorgen and Hantschmann, Markus and Hieke, Florian and Kaya, Sarp and K{\"u}hn, Danilo and LaRue, Jerry and Mercurio, Giuseppe and Minitti, Michael P. and Mitra, Ankush and Moeller, Stefan P. and Ng, May Ling and Nilsson, Anders and Nordlund, Dennis and Norskov, Jens and {\"O}str{\"o}m, Henrik and Ogasawara, Hirohito and Persson, Mats and Schlotter, William F. and Sellberg, Jonas A. and Wolf, Martin and Abild-Pedersen, Frank and Pettersson, Lars G. M. and Wurth, Wilfried}, title = {Chemical Bond Activation Observed with an X-ray Laser}, series = {The journal of physical chemistry letters}, volume = {7}, journal = {The journal of physical chemistry letters}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/acs.jpclett.6b01543}, pages = {3647 -- 3651}, year = {2016}, abstract = {The concept of bonding and antibonding orbitals is fundamental in chemistry. The population of those orbitals and the energetic difference between the two reflect the strength of the bonding interaction. Weakening the bond is expected to reduce this energetic splitting, but the transient character of bond-activation has so far prohibited direct experimental access. Here we apply time-resolved soft X-ray spectroscopy at a free electron laser to directly observe the decreased bonding antibonding splitting following bond-activation using an ultrashort optical laser pulse.}, language = {en} } @article{OstromObergXinetal.2015, author = {Ostrom, H. and Oberg, H. and Xin, H. and Larue, J. and Beye, Martin and Gladh, J. and Ng, M. L. and Sellberg, J. A. and Kaya, S. and Mercurio, G. and Nordlund, D. and Hantschmann, Markus and Hieke, F. and Kuehn, D. and Schlotter, W. F. and Dakovski, G. L. and Turner, J. J. and Minitti, M. P. and Mitra, A. and Moeller, S. P. and F{\"o}hlisch, Alexander and Wolf, M. and Wurth, W. and Persson, Mats and Norskov, J. K. and Abild-Pedersen, Frank and Ogasawara, Hirohito and Pettersson, Lars G. M. and Nilsson, A.}, title = {Probing the transition state region in catalytic CO oxidation on Ru}, series = {Science}, volume = {347}, journal = {Science}, number = {6225}, publisher = {American Assoc. for the Advancement of Science}, address = {Washington}, issn = {0036-8075}, doi = {10.1126/science.1261747}, pages = {978 -- 982}, year = {2015}, abstract = {Femtosecond x-ray laser pulses are used to probe the carbon monoxide (CO) oxidation reaction on ruthenium (Ru) initiated by an optical laser pulse. On a time scale of a few hundred femtoseconds, the optical laser pulse excites motions of CO and oxygen (O) on the surface, allowing the reactants to collide, and, with a transient close to a picosecond (ps), new electronic states appear in the OK-edge x-ray absorption spectrum. Density functional theory calculations indicate that these result from changes in the adsorption site and bond formation between CO and O with a distribution of OC-O bond lengths close to the transition state (TS). After 1 ps, 10\% of the CO populate the TS region, which is consistent with predictions based on a quantum oscillator model.}, language = {en} } @article{OvsyannikovKarlssonLundqvistetal.2013, author = {Ovsyannikov, Ruslan and Karlsson, P. and Lundqvist, M. and Lupulescu, C. and Eberhardt, W. and F{\"o}hlisch, Alexander and Svensson, S. and Martensson, N.}, title = {Principles and operation of a new type of electron spectrometer - ArTOF}, series = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy}, volume = {191}, journal = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy}, number = {12}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0368-2048}, doi = {10.1016/j.elspec.2013.08.005}, pages = {92 -- 103}, year = {2013}, abstract = {A new energy and angular electron analyzer ArTOF (Angular Resolved Time of Flight) is described. The analyzer is based on simultaneous measurement of flight times and angles in an advanced electron lens system. In angular modes the new analyzer combines an increase in transmission by almost three orders of magnitude with improved resolution, in comparison to standard state-of-the-art electron spectrometers. In this report we describe some design principles and we give a review of calibration and alignment procedures necessary for the use of the ArTOF on a synchrotron radiation facility. Our program scripts to handle the large datasets are also discussed. Furthermore we give a broad description of the new research fields that benefit from the use of the ArTOF and give a short summary of the first results of angle resolved photoemission measurement with ArTOF using the single-bunch X-ray pulses from the BESSY II storage ring facility. (C) 2013 Published by Elsevier B.V.}, language = {en} } @article{KunnusJosefssonSchrecketal.2013, author = {Kunnus, Kristjan and Josefsson, Ida and Schreck, Simon and Quevedo, Wilson and Miedema, Piter S. and Techert, Simone and de Groot, Frank M. F. and Odelius, Michael and Wernet, Philippe and F{\"o}hlisch, Alexander}, title = {From Ligand Fields to Molecular Orbitals: Probing the Local Valence Electronic Structure of Ni2+ in Aqueous Solution with Resonant Inelastic X-ray Scattering}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {117}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, number = {51}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/jp4100813}, pages = {16512 -- 16521}, year = {2013}, abstract = {Bonding of the Ni2+(aq) complex is investigated with an unprecedented combination of resonant inelastic X-ray scattering (RIXS) measurements and ab initio calculations at the Ni L absorption edge. The spectra directly reflect the relative energies of the ligand-field and charge-transfer valence-excited states. They give element-specific access with atomic resolution to the ground-state electronic structure of the complex and allow quantification of ligand-field strength and 3d-3d electron correlation interactions in the Ni2+(aq) complex. The experimentally determined ligand-field strength is 10Dq = 1.1 eV. This and the Racah parameters characterizing 3d-3d Coulomb interactions B = 0.13 eV and C = 0.42 eV as readily derived from the measured energies match very well with the results from UV-vis spectroscopy. Our results demonstrate how L-edge RIXS can be used to complement existing spectroscopic tools for the investigation of bonding in 3d transition-metal coordination compounds in solution. The ab initio RASPT2 calculation is successfully used to simulate the L-edge RIXS spectra.}, language = {en} } @article{BeyeFoehlisch2013, author = {Beye, Martin and F{\"o}hlisch, Alexander}, title = {Soft X-ray probes of ultrafast dynamics for heterogeneous catalysis}, series = {Chemical physics : a journal devoted to experimental and theoretical research involving problems of both a chemical and physical nature}, volume = {414}, journal = {Chemical physics : a journal devoted to experimental and theoretical research involving problems of both a chemical and physical nature}, number = {5}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0301-0104}, doi = {10.1016/j.chemphys.2012.03.023}, pages = {130 -- 138}, year = {2013}, abstract = {Soft X-ray spectroscopy is one of the best tools to directly address the electronic structure, the driving force of chemical reactions. It enables selective studies on sample surfaces to single out reaction centers in heterogeneous catalytic reactions. With core-hole clock methods, specific dynamics are related to the femtosecond life time of a core-hole. Typically, this method is used with photoemission spectroscopy, but advancements in soft X-ray emission techniques render more specific studies possible. With the advent of bright femtosecond pulsed soft X-ray sources, highly selective pump-probe X-ray emission studies are enabled with temporal resolutions down to tens of femtoseconds. This finally allows to study dynamics in the electronic structure of adsorbed reaction centers on the whole range of relevant time scales - closing the gap between kinetic soft X-ray studies and the atto- to femtosecond core-hole clock techniques.}, language = {en} } @article{KoenneckeFollathPontiusetal.2013, author = {K{\"o}nnecke, Rene and Follath, R. and Pontius, N. and Schlappa, J. and Eggenstein, F. and Zeschke, T. and Bischoff, P. and Schmidt, J. -S. and Noll, T. and Trabant, C. and Schreck, S. and Wernet, Ph. and Eisebitt, S. and Senf, F. and Schuessler-Langeheine, Christian and Erko, A. and F{\"o}hlisch, Alexander}, title = {The confocal plane grating spectrometer at BESSY II}, series = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy}, volume = {188}, journal = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0368-2048}, doi = {10.1016/j.elspec.2012.11.003}, pages = {133 -- 139}, year = {2013}, abstract = {At BESSY II a confocal plane grating spectrometer for resonant inelastic X-ray scattering (RIXS) is currently under commissioning. The new endstation operates with a source size of 4 x 1 mu m(2) provided by its dedicated beamline. The RIXS-spectrometer covers an energy range from 50 eV to 1000 eV, providing a resolving power E/Delta E of 5000-15,000. The beamline allows full polarization control and gives a photon flux of up to 7 x 10(14) photons/s/0.1 A/0.1\%bandwidth by offering a resolving power E/Delta E of 4000-12,000.}, language = {en} } @article{BeyeWernetSchuesslerLangeheineetal.2013, author = {Beye, Martin and Wernet, Ph. and Sch{\"u}ßler-Langeheine, Christian and F{\"o}hlisch, Alexander}, title = {Time resolved resonant inelastic X-ray scattering: a supreme tool to understand dynamics in solids and molecules}, series = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy}, volume = {188}, journal = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy}, number = {3}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0368-2048}, doi = {10.1016/j.elspec.2013.04.013}, pages = {172 -- 182}, year = {2013}, abstract = {Dynamics in materials typically involve different degrees of freedom, like charge, lattice, orbital and spin in a complex interplay. Time-resolved resonant inelastic X-ray scattering (RIXS) as a highly selective tool can provide unique insight and follow the details of dynamical processes while resolving symmetries, chemical and charge states, momenta, spin configurations, etc. In this paper, we review examples where the intrinsic scattering duration time is used to study femtosecond phenomena. Free-electron lasers access timescales starting in the sub-ps range through pump-probe methods and synchrotrons study the time scales longer than tens of ps. In these examples, time-resolved resonant inelastic X-ray scattering is applied to solids as well as molecular systems.}, language = {en} } @article{MiedemaBeyeKoenneckeetal.2014, author = {Miedema, P. S. and Beye, Martin and Koennecke, R. and Schiwietz, G. and F{\"o}hlisch, Alexander}, title = {The angular- and crystal-momentum transfer through electron-phonon coupling in silicon and silicon-carbide: similarities and differences}, series = {New journal of physics : the open-access journal for physics}, volume = {16}, journal = {New journal of physics : the open-access journal for physics}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1367-2630}, doi = {10.1088/1367-2630/16/9/093056}, pages = {17}, year = {2014}, abstract = {Electron-phonon scattering has been studied for silicon carbide (6H-SiC) with resonant inelastic x-ray scattering at the silicon 2p edge. The observed electron-phonon scattering yields a crystal momentum transfer rate per average phonon in 6H-SiC of 1.8 fs(-1) while it is 0.2 fs(-1) in crystalline silicon. The angular momentum transfer rate per average phonon for 6H-SiC is 0.1 fs(-1), which is much higher than 0.0035 fs(-1) obtained for crystalline silicon in a previous study. The higher electron-phonon scattering rates in 6H-SiC are a result of the larger electron localization at the silicon atoms in 6H-SiC as compared to crystalline silicon. While delocalized valence electrons can screen effectively (part of) the electron-phonon interaction, this effect is suppressed for 6H-SiC in comparison to crystalline silicon. Smaller contributions to the difference in electron-phonon scattering rates between 6H-SiC and silicon arise from the lower atomic mass of carbon versus silicon and the difference in local symmetry.}, language = {en} } @article{WernetKunnusJosefssonetal.2015, author = {Wernet, Philippe and Kunnus, Kristjan and Josefsson, Ida and Rajkovic, Ivan and Quevedo, Wilson and Beye, Martin and Schreck, Simon and Gruebel, S. and Scholz, Mirko and Nordlund, Dennis and Zhang, Wenkai and Hartsock, Robert W. and Schlotter, William F. and Turner, Joshua J. and Kennedy, Brian and Hennies, Franz and de Groot, Frank M. F. and Gaffney, Kelly J. and Techert, Simone and Odelius, Michael and F{\"o}hlisch, Alexander}, title = {Orbital-specific mapping of the ligand exchange dynamics of Fe(CO)(5) in solution}, series = {Nature : the international weekly journal of science}, volume = {520}, journal = {Nature : the international weekly journal of science}, number = {7545}, publisher = {Nature Publ. Group}, address = {London}, issn = {0028-0836}, doi = {10.1038/nature14296}, pages = {78 -- 81}, year = {2015}, abstract = {Transition-metal complexes have long attracted interest for fundamental chemical reactivity studies and possible use in solar energy conversion(1,2). Electronic excitation, ligand loss from the metal centre, or a combination of both, creates changes in charge and spin density at the metal site(3-11) that need to be controlled to optimize complexes for photocatalytic hydrogen production(8) and selective carbon-hydrogen bond activation(9-11). An understanding at the molecular level of how transition-metal complexes catalyse reactions, and in particular of the role of the short-lived and reactive intermediate states involved, will be critical for such optimization. However, suitable methods for detailed characterization of electronic excited states have been lacking. Here we show, with the use of X-ray laser-based femtosecond-resolution spectroscopy and advanced quantum chemical theory to probe the reaction dynamics of the benchmark transition-metal complex Fe(CO)(5) in solution, that the photo-induced removal of CO generates the 16-electron Fe(CO)(4) species, a homogeneous catalyst(12,13) with an electron deficiency at the Fe centre(14,15), in a hitherto unreported excited singlet state that either converts to the triplet ground state or combines with a CO or solvent molecule to regenerate a penta-coordinated Fe species on a sub-picosecond timescale. This finding, which resolves the debate about the relative importance of different spin channels in the photochemistry of Fe(CO)(5) (refs 4, 16-20), was made possible by the ability of femtosecond X-ray spectroscopy to probe frontier-orbital interactions with atom specificity. We expect the method to be broadly applicable in the chemical sciences, and to complement approaches that probe structural dynamics in ultrafast processes.}, language = {en} } @article{XinLaRueObergetal.2015, author = {Xin, Hong and LaRue, Jerry and Oberg, Henrik and Beye, Martin and Turner, J. J. and Gladh, J{\"o}rgen and Ng, May L. and Sellberg, Jonas A. and Kaya, Sarp and Mercurio, G. and Hieke, F. and Nordlund, Dennis and Schlotter, William F. and Dakovski, Georgi L. and Minitti, Michael P. and F{\"o}hlisch, Alexander and Wolf, Martin and Wurth, Wilfried and Ogasawara, Hirohito and Norskov, Jens K. and Ostrom, Henrik and Pettersson, Lars G. M. and Nilsson, Anders and Abild-Pedersen, Frank}, title = {Strong Influence of Coadsorbate Interaction on CO Desorption Dynamics on Ru(0001) Probed by Ultrafast X-Ray Spectroscopy and Ab Initio Simulations}, series = {Physical review letters}, volume = {114}, journal = {Physical review letters}, number = {15}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.114.156101}, pages = {6}, year = {2015}, abstract = {We show that coadsorbed oxygen atoms have a dramatic influence on the CO desorption dynamics from Ru(0001). In contrast to the precursor-mediated desorption mechanism on Ru(0001), the presence of surface oxygen modifies the electronic structure of Ru atoms such that CO desorption occurs predominantly via the direct pathway. This phenomenon is directly observed in an ultrafast pump-probe experiment using a soft x-ray free-electron laser to monitor the dynamic evolution of the valence electronic structure of the surface species. This is supported with the potential of mean force along the CO desorption path obtained from density-functional theory calculations. Charge density distribution and frozen-orbital analysis suggest that the oxygen-induced reduction of the Pauli repulsion, and consequent increase of the dative interaction between the CO 5 sigma and the charged Ru atom, is the electronic origin of the distinct desorption dynamics. Ab initio molecular dynamics simulations of CO desorption from Ru(0001) and oxygen-coadsorbed Ru(0001) provide further insights into the surface bond-breaking process.}, language = {en} } @article{FoersterLindenauLeyendeckeretal.2015, author = {F{\"o}rster, Daniel F. and Lindenau, Bernd and Leyendecker, Marko and Janssen, Franz and Winkler, Carsten and Schumann, Frank O. and Kirschner, Juergen and Holldack, Karsten and F{\"o}hlisch, Alexander}, title = {Phase-locked MHz pulse selector for x-ray sources}, series = {Optics letters : a publication of the Optical Society of America}, volume = {40}, journal = {Optics letters : a publication of the Optical Society of America}, number = {10}, publisher = {Optical Society of America}, address = {Washington}, issn = {0146-9592}, doi = {10.1364/OL.40.002265}, pages = {2265 -- 2268}, year = {2015}, abstract = {Picosecond x-ray pulses are extracted with a phase-locked x-ray pulse selector at 1.25 MHz repetition rate from the pulse trains of the accelerator-driven multiuser x-ray source BESSY II preserving the peak brilliance at high pulse purity. The system consists of a specially designed in-vacuum chopper wheel rotating with approximate to 1 kHz angular frequency. The wheel is driven in an ultrahigh vacuum and is levitated on magnetic bearings being capable of withstanding high centrifugal forces. Pulses are picked by 1252 high-precision slits of 70 mu m width on the outer rim of the wheel corresponding to a temporal opening window of the chopper of 70 ns. We demonstrate how the electronic phase stabilization of +/- 2 ns together with an arrival time jitter of the individual slits of the same order of magnitude allows us to pick short single bunch x-ray pulses out of a 200 ns ion clearing gap in a multibunch pulse train as emitted from a synchrotron facility at 1.25 MHz repetition rate with a pulse purity below the shot noise detection limit. The approach is applicable to any high-repetition pulsed radiation source, in particular in the x-ray spectral range up to 10 keV. The opening window in a real x-ray beamline, its stability, as well as the limits of mechanical pulse picking techniques in the MHz range are discussed. (C) 2015 Optical Society of America}, language = {en} } @article{BeyeFoehlisch2011, author = {Beye, Martin and F{\"o}hlisch, Alexander}, title = {A soft X-ray approach to electron-phonon interactions beyond the Born-Oppenheimer approximation}, series = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy}, volume = {184}, journal = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy}, number = {3-6}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0368-2048}, doi = {10.1016/j.elspec.2010.12.032}, pages = {313 -- 317}, year = {2011}, abstract = {With modern soft X-ray methods, the whole field of electron-phonon interactions becomes accessible directly in the ultrafast time domain with ultrashort pulsed X-ray sources, as well as in the energy domain through modern highly resolving spectrometers. The well-known core-hole clock approach plays an intermediate role, resolving energetic and temporal features at the same time. In this perspective paper, we review several experiments to illustrate the modern advances in the selective study of electron-phonon interactions as fundamentally determining ingredients for materials properties. We present the different complementary approaches that can be taken with soft X-ray methods to conquer this field beyond the Born-Oppenheimer approximation.}, language = {en} } @unpublished{FoehlischdeGrootOdeliusetal.2014, author = {F{\"o}hlisch, Alexander and de Groot, F. M. F. and Odelius, Michael and Techert, Simone and Wernet, P.}, title = {Comment on "state-dependent electron delocalization dynamics at the solute-solvent interface: soft-x-ray absorption spectroscopy and lambda b initio calculations"}, series = {Physical review letters}, volume = {112}, journal = {Physical review letters}, number = {12}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.112.129302}, pages = {2}, year = {2014}, language = {en} } @article{KunnusSchreckFoehlisch2015, author = {Kunnus, Kristjan and Schreck, Simon and F{\"o}hlisch, Alexander}, title = {Free-electron laser based resonant inelastic X-ray scattering on molecules and liquids}, series = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy}, volume = {204}, journal = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0368-2048}, doi = {10.1016/j.elspec.2015.08.012}, pages = {345 -- 355}, year = {2015}, abstract = {The unprecedented beam properties of free-electron laser based X-ray sources enable novel resonant inelastic X-ray scattering (RIXS) experiments. Femtosecond time-resolved RIXS can be used to follow charge, spin and structural dynamics of dilute solute molecules in solution. Ultrashort X-ray pulses allow probing of highly radiation sensitive states of matter such as the metastable phase of supercooled liquid water. Nonlinear X-ray probes like amplified spontaneous emission and stimulated resonant X-ray scattering provide an enhanced selectivity and sensitivity as well as a path to control radiation damage and increase the photon yields in RIXS experiments. (C) 2015 Elsevier B.V. All rights reserved.}, language = {en} } @article{WernetKunnusSchrecketal.2012, author = {Wernet, Philippe and Kunnus, Kristjan and Schreck, Simon and Quevedo, Wilson and Kurian, Reshmi and Techert, Simone and de Groot, Frank M. F. and Odelius, Michael and F{\"o}hlisch, Alexander}, title = {Dissecting local atomic and intermolecular interactions of transition-metal ions in solution with selective X-ray spectroscopy}, series = {The journal of physical chemistry letters}, volume = {3}, journal = {The journal of physical chemistry letters}, number = {23}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/jz301486u}, pages = {3448 -- 3453}, year = {2012}, abstract = {Determining covalent and charge-transfer contributions to bonding in solution has remained an experimental challenge. Here, the quenching of fluorescence decay channels as expressed in dips in the L-edge X-ray spectra of solvated 3d transition-metal ions and complexes was reported as a probe. With a full set of experimental and theoretical ab initio L-edge X-ray spectra of aqueous Cr3+, including resonant inelastic X-ray scattering, we address covalency and charge transfer for this prototypical transition-metal ion in solution. We dissect local atomic effects from intermolecular interactions and quantify X-ray optical effects. We find no evidence for the asserted ultrafast charge transfer to the solvent and show that the dips are readily explained by X-ray optical effects and local atomic state dependence of the fluorescence yield. Instead, we find, besides ionic interactions, a covalent contribution to the bonding in the aqueous complex of ligand-to-metal charge-transfer character.}, language = {en} } @article{MiedemaWernetFoehlisch2014, author = {Miedema, Piter S. and Wernet, Philippe and F{\"o}hlisch, Alexander}, title = {State-dependent fluorescence yields through the core-valence Coulomb exchange parameter}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {89}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {1050-2947}, doi = {10.1103/PhysRevA.89.052507}, pages = {7}, year = {2014}, abstract = {Total and partial fluorescence yield (PFY) L-edge x-ray absorption spectra differ from the transmission x-ray absorption spectra (XAS) through state-dependent fluorescence yield across the XAS. For 3d(1) to 3d(9) in octahedral symmetry we apply simulations of PFY and XAS and show how the atomic 2p3d Coulomb exchange parameter G(pd) governs the differences in the L-3/(L-2 + L-3) branching ratio between PFY and XAS. G(pd) orders the XAS final states following Hund's rules creating a strong state-dependent fluorescence decay strength variation across the XAS leading to the differences between PFY and XAS.}, language = {en} } @article{ThielemannKuehnHoffmannFoehlisch2012, author = {Thielemann-K{\"u}hn, Nele and Hoffmann, P. and F{\"o}hlisch, Alexander}, title = {A versatile detector for total fluorescence and electron yield experiments}, series = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques}, volume = {83}, journal = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques}, number = {9}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0034-6748}, doi = {10.1063/1.4754126}, pages = {3}, year = {2012}, abstract = {The combination of a non-coated silicon photodiode with electron repelling meshes makes a versatile detector for total fluorescence yield and electron yield techniques highly suitable for x-ray absorption spectroscopy. In particular, a copper mesh with a bias voltage allows to suppress or transmit the electron yield signal. The performance of this detection scheme has been characterized by near edge x-ray absorption fine structure studies of thermal oxidized silicon and sapphire. The results show that the new detector probes both electron yield and for a bias voltage exceeding the maximum photon energy the total fluorescence yield.}, language = {en} } @article{MiedemaBeyeKoenneckeetal.2014, author = {Miedema, Piter Sybren and Beye, Martin and Koennecke, R. and Schiwietz, Gregor and F{\"o}hlisch, Alexander}, title = {Thermal evolution of the band edges of 6H-SiC: X-ray methods compared to the optical band gap}, series = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy}, volume = {197}, journal = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0368-2048}, doi = {10.1016/j.elspec.2014.08.003}, pages = {37 -- 42}, year = {2014}, abstract = {The band gap of semiconductors like silicon and silicon carbide (SIC) is the key for their device properties. In this research, the band gap of 6H-SiC and its temperature dependence were analyzed with silicon 2p X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant inelastic X-ray scattering (RIXS) allowing for a separate analysis of the conduction-band minimum (CBM) and valence-band maximum (VBM) components of the band gap. The temperature-dependent asymmetric band gap shrinking of 6H-SiC was determined with a valence-band slope of +2.45 x 10(-4) eV/K and a conduction-band slope of -1.334 x 10(-4) eV/K. The apparent asymmetry, e.g., that two thirds of the band-gap shrinking with increasing temperature is due to the VBM evolution in 6H-SiC, is similar to the asymmetry obtained for pure silicon before. The overall band gap temperature-dependence determined with XAS and nonresonant XES is compared to temperature-dependent optical studies. The core-excitonic binding energy appearing in the Si 2p XAS is extracted as the main difference. In addition, the energy loss of the onset of the first band in RIXS yields to values similar to the optical band gap over the tested temperature range. (C) 2014 Elsevier B.V. All rights reserved.}, language = {en} } @article{HolldackOvsyannikovKuskeetal.2014, author = {Holldack, Karsten and Ovsyannikov, Ruslan and Kuske, P. and Mueller, R. and Schaelicke, A. and Scheer, M. and Gorgoi, Mihaela and Kuehn, D. and Leitner, T. and Svensson, S. and Martensson, N. and F{\"o}hlisch, Alexander}, title = {Single bunch X-ray pulses on demand from a multi-bunch synchrotron radiation source}, series = {Nature Communications}, volume = {5}, journal = {Nature Communications}, publisher = {Nature Publ. Group}, address = {London}, issn = {2041-1723}, doi = {10.1038/ncomms5010}, pages = {7}, year = {2014}, abstract = {Synchrotron radiation facilities routinely operate in a multi-bunch regime, but applications relying on time-of-flight schemes require single bunch operation. Here we show that pulse picking by resonant excitation in a storage ring creates in addition to the multi-bunch operation a distinct and separable single bunch soft X-ray source. It has variable polarization, a photon flux of up to 10(7)-10(9) ph s(-1)/0.1\%BW at purity values of 10(4)-10(2) and a repetition rate of 1.25 MHz. The quasi-resonant excitation of incoherent betatron oscillations of electrons allows horizontal pulse separation at variable (also circular) polarization accessible for both, regular 30 ps pulses and ultrashort pulses of 2-3 ps duration. Combined with a new generation of angularly resolving electron spectrometers this creates unique opportunities for time-resolved photoemission studies as confirmed by time-of-flight spectra. Our pulse picking scheme is particularly suited for surface physics at diffraction-limited light sources promising ultimate spectral resolution.}, language = {en} } @article{KunnusJosefssonRajkovicetal.2016, author = {Kunnus, Kristjan and Josefsson, Ida and Rajkovic, Ivan and Schreck, Simon and Quevedo, Wilson and Beye, Martin and Gr{\"u}bel, Sebastian and Scholz, Mirko and Nordlund, Dennis and Zhang, Wenkai and Hartsock, Robert W. and Gaffney, Kelly J. and Schlotter, William F. and Turner, Joshua J. and Kennedy, Brian and Hennies, Franz and Techert, Simone and Wernet, Philippe and Odelius, Michael and F{\"o}hlisch, Alexander}, title = {Anti-Stokes resonant x-ray Raman scattering for atom specific and excited state selective dynamics}, series = {NEW JOURNAL OF PHYSICS}, volume = {18}, journal = {NEW JOURNAL OF PHYSICS}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {1367-2630}, doi = {10.1088/1367-2630/18/10/103011}, pages = {9}, year = {2016}, abstract = {Ultrafast electronic and structural dynamics of matter govern rate and selectivity of chemical reactions, as well as phase transitions and efficient switching in functional materials. Since x-rays determine electronic and structural properties with elemental, chemical, orbital and magnetic selectivity, short pulse x-ray sources have become central enablers of ultrafast science. Despite of these strengths, ultrafast x-rays have been poor at picking up excited state moieties from the unexcited ones. With time-resolved anti-Stokes resonant x-ray Raman scattering (AS-RXRS) performed at the LCLS, and ab initio theory we establish background free excited state selectivity in addition to the elemental, chemical, orbital and magnetic selectivity of x-rays. This unparalleled selectivity extracts low concentration excited state species along the pathway of photo induced ligand exchange of Fe(CO)(5) in ethanol. Conceptually a full theoretical treatment of all accessible insights to excited state dynamics with AS-RXRS with transform-limited x-ray pulses is given-which will be covered experimentally by upcoming transform-limited x-ray sources.}, language = {en} } @article{KunnusJosefssonRajkovicetal.2016, author = {Kunnus, Kristjan and Josefsson, I. and Rajkovic, Ivan and Schreck, Simon and Quevedo, Wilson and Beye, Martin and Weniger, C. and Gruebel, S. and Scholz, M. and Nordlund, D. and Zhang, W. and Hartsock, R. W. and Gaffney, K. J. and Schlotter, W. F. and Turner, J. J. and Kennedy, B. and Hennies, F. and de Groot, F. M. F. and Techert, S. and Odelius, Michael and Wernet, Ph. and F{\"o}hlisch, Alexander}, title = {Identification of the dominant photochemical pathways and mechanistic insights to the ultrafast ligand exchange of Fe(CO)(5) to Fe(CO)(4)EtOH}, series = {Structural dynamics}, volume = {3}, journal = {Structural dynamics}, publisher = {American Institute of Physics}, address = {Washington}, issn = {2329-7778}, doi = {10.1063/1.4941602}, pages = {16}, year = {2016}, abstract = {We utilized femtosecond time-resolved resonant inelastic X-ray scattering and ab initio theory to study the transient electronic structure and the photoinduced molecular dynamics of a model metal carbonyl photocatalyst Fe(CO)(5) in ethanol solution. We propose mechanistic explanation for the parallel ultrafast intra-molecular spin crossover and ligation of the Fe(CO)(4) which are observed following a charge transfer photoexcitation of Fe(CO)(5) as reported in our previous study [ Wernet et al., Nature 520, 78 (2015)]. We find that branching of the reaction pathway likely happens in the (1)A(1) state of Fe(CO)(4). A sub-picosecond time constant of the spin crossover from B-1(2) to B-3(2) is rationalized by the proposed B-1(2) -> (1)A(1) -> B-3(2) mechanism. Ultrafast ligation of the B-1(2) Fe(CO)(4) state is significantly faster than the spin-forbidden and diffusion limited ligation process occurring from the B-3(2) Fe(CO)(4) ground state that has been observed in the previous studies. We propose that the ultrafast ligation occurs via B-1(2) -> (1)A(1) -> (1)A'Fe(CO)(4)EtOH pathway and the time scale of the (1)A(1) Fe(CO)(4) state ligation is governed by the solute-solvent collision frequency. Our study emphasizes the importance of understanding the interaction of molecular excited states with the surrounding environment to explain the relaxation pathways of photoexcited metal carbonyls in solution. (C) 2016 Author(s).}, language = {en} } @article{KunnusZhangDelceyetal.2016, author = {Kunnus, Kristjan and Zhang, Wenkai and Delcey, Mickael G. and Pinjari, Rahul V. and Miedema, Piter S. and Schreck, Simon and Quevedo, Wilson and Schr{\"o}der, Henning and F{\"o}hlisch, Alexander and Gaffney, Kelly J. and Lundberg, Marcus and Odelius, Michael and Wernet, Philippe}, title = {Viewing the Valence Electronic Structure of Ferric and Ferrous Hexacyanide in Solution from the Fe and Cyanide Perspectives}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {120}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.6b04751}, pages = {7182 -- 7194}, year = {2016}, abstract = {The valence-excited states of ferric and ferrous hexacyanide ions in aqueous solution were mapped by resonant inelastic X-ray scattering (RIXS) at the Fe L-2,L-3 and N K edges. Probing of both the central Fe and the ligand N atoms enabled identification of the metal-and ligand-centered excited states, as well as ligand-to-metal and metal-to-ligand charge-transfer excited states. Ab initio calculations utilizing the RASPT2 method were used to simulate the Fe L-2,L-3-edge RIXS spectra and enabled quantification of the covalencies of both occupied and empty orbitals of pi and sigma symmetry. We found that pi back-donation in the ferric complex is smaller than that in the ferrous complex. This is evidenced by the relative amounts of Fe 3d character in the nominally 2 pi CN- molecular orbital of 7\% and 9\% in ferric and ferrous hexacyanide, respectively. Utilizing the direct sensitivity of Fe L-3-edge RIXS to the Fe 3d character in the occupied molecular orbitals, we also found that the donation interactions are dominated by sigma bonding. The latter was found to be stronger in the ferric complex, with an Fe 3d contribution to the nominally 5 sigma CN- molecular orbitals of 29\% compared to 20\% in the ferrous complex. These results are consistent with the notion that a higher charge at the central metal atom increases donation and decreases back-donation.}, language = {en} } @book{Foehlisch2010, author = {F{\"o}hlisch, Alexander}, title = {Phasen{\"u}berg{\"a}nge und Ultrakurzzeitdynamik : Antrittsvorlesung 2010-05-12}, publisher = {Univ.-Bibl.}, address = {Potsdam}, year = {2010}, abstract = {F{\"o}hlisch wird in seinem Vortrag die großen Zukunftsthemen der Mensch streifen: Energie, Umwelt und Struktur der Materie. Die Komplexit{\"a}t ihrer elementaren Prozesse erfordert die komplement{\"a}re Betrachtung der damit verbundene Dimensionen von Energie, Zeit und Raum. Dies l{\"a}sst sich inzwischen mit Synchrotronstrahlungsquellen in gr{\"o}ßter Pr{\"a}ision darstellen.}, language = {de} } @article{WernetLeitnerJosefssonetal.2017, author = {Wernet, Philippe and Leitner, T. and Josefsson, Ida and Mazza, T. and Miedema, P. S. and Schroder, H. and Beye, Martin and Kunnus, K. and Schreck, S. and Radcliffe, P. and Dusterer, S. and Meyer, M. and Odelius, Michael and Fohlisch, Alexander}, title = {Communication: Direct evidence for sequential dissociation of gas-phase Fe(CO)(5) via a singlet pathway upon excitation at 266 nm}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {146}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.4984774}, pages = {5}, year = {2017}, abstract = {We prove the hitherto hypothesized sequential dissociation of Fe(CO)(5) in the gas phase upon photoexcitation at 266 nm via a singlet pathway with time-resolved valence and core-level photoelectron spectroscopy with an x-ray free-electron laser. Valence photoelectron spectra are used to identify free CO molecules and to determine the time constants of stepwise dissociation to Fe(CO)(4) within the temporal resolution of the experiment and further to Fe(CO)(3) within 3 ps. Fe 3p core-level photoelectron spectra directly reflect the singlet spin state of the Fe center in Fe(CO)(5), Fe(CO)(4), and Fe(CO)(3) showing that the dissociation exclusively occurs along a singlet pathway without triplet-state contribution. Our results are important for assessing intra- and intermolecular relaxation processes in the photodissociation dynamics of the prototypical Fe(CO)(5) complex in the gas phase and in solution, and they establish time-resolved core-level photoelectron spectroscopy as a powerful tool for determining the multiplicity of transition metals in photochemical reactions of coordination complexes. Published by AIP Publishing.}, language = {en} } @article{NiskanenJankalaHuttulaetal.2017, author = {Niskanen, Johannes and Jankala, Kari and Huttula, Marco and F{\"o}hlisch, Alexander}, title = {QED effects in 1s and 2s single and double ionization potentials of the noble gases}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {146}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.4979991}, pages = {1443 -- 1450}, year = {2017}, abstract = {We present calculations on the quantum electrodynamics (QED) effects in 1s and 2s single and double ionization potentials of noble gases from Ne to Rn as perturbations on relativistic four-component Dirac-Fock wavefunctions. The most dominant effect originates from the self-energy of the core-electron that yields corrections of similar order as the transverse interaction. For 1s ionization potentials, a match within few eV against the known experimental values is obtained, and our work reveals considerable QED effects in the photoelectron binding energies across the periodic table-most strikingly even for Ne. We perform power-law fits for the corrections as a function of Z and interpolate the QED correction of similar to-0.55 eV for S1s. Due to this, the K-edge electron spectra of the third row and below need QED for a match in the absolute energy when using state-of-the-art instrumentation. Published by AIP Publishing.}, language = {en} } @article{NiskanenSahleGilmoreetal.2017, author = {Niskanen, Johannes and Sahle, Christoph J. and Gilmore, Keith and Uhlig, Frank and Smiatek, Jens and F{\"o}hlisch, Alexander}, title = {Disentangling structural information from core-level excitation spectra}, series = {Physical review : E, Statistical, nonlinear and soft matter physics}, volume = {96}, journal = {Physical review : E, Statistical, nonlinear and soft matter physics}, publisher = {American Physical Society}, address = {College Park}, issn = {2470-0045}, doi = {10.1103/PhysRevE.96.013319}, pages = {8}, year = {2017}, abstract = {Core-level spectra of liquids can be difficult to interpret due to the presence of a range of local environments. We present computational methods for investigating core-level spectra based on the idea that both local structural parameters and the x-ray spectra behave as functions of the local atomic configuration around the absorbing site. We identify correlations between structural parameters and spectral intensities in defined regions of interest, using the oxygen K-edge excitation spectrum of liquid water as a test case. Our results show that this kind of analysis can find the main structure-spectral relationships of ice, liquid water, and supercritical water.}, language = {en} } @article{HantschmannFoehlisch2022, author = {Hantschmann, Markus and F{\"o}hlisch, Alexander}, title = {A rate model approach for FEL pulse induced transmissions changes, saturable absorption, X-ray transparency and stimulated emission}, series = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy}, volume = {256}, journal = {Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0368-2048}, doi = {10.1016/j.elspec.2021.147139}, pages = {9}, year = {2022}, abstract = {As the use of free electron laser (FEL) sources increases, so do the findings mentioning non-linear phenomena occurring at these experiments, such as saturable absorption, induced transparency and scattering breakdowns. These are well known among the laser community, but are still rarely understood and expected among the X-ray community and to date lack tools and theories to accurately predict the respective experimental parameters and results. We present a simple theoretical framework to access short X-ray pulse induced light- matter interactions which occur at intense short X-ray pulses as available at FEL sources. Our approach allows to investigate effects such as saturable absorption, induced transparency and scattering suppression, stimulated emission, and transmission spectra, while including the density of state influence relevant to soft X-ray spectroscopy in, for example, transition metal complexes or functional materials. This computationally efficient rate model based approach is intuitively adaptable to most solid state sample systems in the soft X-ray spectrum with the potential to be extended for liquid and gas sample systems as well. The feasibility of the model to estimate the named effects and the influence of the density of state is demonstrated using the example of CoPd transition metal systems at the Co edge. We believe this work is an important contribution for the preparation, performance, and understanding of FEL based high intensity and short pulse experiments, especially on functional materials in the soft X-ray spectrum.}, language = {en} } @article{MartenssonFoehlischSvensson2022, author = {Martensson, Nils and F{\"o}hlisch, Alexander and Svensson, Svante}, title = {Uppsala and Berkeley}, series = {Journal of vacuum science \& technology : JVST ; an AVS journal / A}, volume = {40}, journal = {Journal of vacuum science \& technology : JVST ; an AVS journal / A}, number = {4}, publisher = {American Institute of Physics}, address = {New York}, issn = {0734-2101}, doi = {10.1116/6.0001879}, pages = {11}, year = {2022}, abstract = {The development of modern photoelectron spectroscopy is reviewed with a special focus on the importance of research at Uppsala University and at Berkeley. The influence of two pioneers, Kai Siegbahn and Dave Shirley, is underlined. Early interaction between the two centers helped to kick-start the field. Both laboratories have continued to play an important role in the field, both in terms of creating new experimental capabilities and developing the theoretical understanding of the spectroscopic processes.}, language = {en} } @article{SunHenniesPietzschetal.2011, author = {Sun, Y. -P. and Hennies, Franz and Pietzsch, Annette and Kennedy, B. and Schmitt, Thorsten and Strocov, Vladimir N. and Andersson, Joakim and Berglund, Martin and Rubensson, Jan-Erik and Aidas, K. and Gel'mukhanov, F. and Odelius, Michael and F{\"o}hlisch, Alexander}, title = {Intramolecular soft modes and intermolecular interactions in liquid acetone}, series = {Physical review : B, Condensed matter and materials physics}, volume = {84}, journal = {Physical review : B, Condensed matter and materials physics}, number = {13}, publisher = {American Physical Society}, address = {College Park}, issn = {1098-0121}, doi = {10.1103/PhysRevB.84.132202}, pages = {4}, year = {2011}, abstract = {Resonant inelastic x-ray scattering spectra excited at the O1s(-1)pi* resonance of liquid acetone are presented. Scattering to the electronic ground state shows a resolved vibrational progression where the dominant contribution is due to the C-O stretching mode, thus demonstrating a unique sensitivity of the method to the local potential energy surface in complex molecular systems. For scattering to electronically excited states, soft vibrational modes and, to a smaller extent, intermolecular interactions give a broadening, which blurs the vibrational fine structure. It is predicted that environmental broadening is dominant in aqueous acetone.}, language = {en} } @article{KubinGuoKrolletal.2018, author = {Kubin, Markus and Guo, Meiyuan and Kroll, Thomas and Loechel, Heike and Kallman, Erik and Baker, Michael L. and Mitzner, Rolf and Gul, Sheraz and Kern, Jan and F{\"o}hlisch, Alexander and Erko, Alexei and Bergmann, Uwe and Yachandra, Vittal and Yano, Junko and Lundberg, Marcus and Wernet, Philippe}, title = {Probing the oxidation state of transition metal complexes}, series = {Chemical science}, volume = {9}, journal = {Chemical science}, number = {33}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2041-6520}, doi = {10.1039/c8sc00550h}, pages = {6813 -- 6829}, year = {2018}, abstract = {Transition metals in inorganic systems and metalloproteins can occur in different oxidation states, which makes them ideal redox-active catalysts. To gain a mechanistic understanding of the catalytic reactions, knowledge of the oxidation state of the active metals, ideally in operando, is therefore critical. L-edge X-ray absorption spectroscopy (XAS) is a powerful technique that is frequently used to infer the oxidation state via a distinct blue shift of L-edge absorption energies with increasing oxidation state. A unified description accounting for quantum-chemical notions whereupon oxidation does not occur locally on the metal but on the whole molecule and the basic understanding that L-edge XAS probes the electronic structure locally at the metal has been missing to date. Here we quantify how charge and spin densities change at the metal and throughout the molecule for both redox and core-excitation processes. We explain the origin of the L-edge XAS shift between the high-spin complexes Mn-II(acac)(2) and Mn-III(acac)(3) as representative model systems and use ab initio theory to uncouple effects of oxidation-state changes from geometric effects. The shift reflects an increased electron affinity of Mn-III in the core-excited states compared to the ground state due to a contraction of the Mn 3d shell upon core-excitation with accompanied changes in the classical Coulomb interactions. This new picture quantifies how the metal-centered core hole probes changes in formal oxidation state and encloses and substantiates earlier explanations. The approach is broadly applicable to mechanistic studies of redox-catalytic reactions in molecular systems where charge and spin localization/delocalization determine reaction pathways.}, language = {en} } @misc{NiskanenKooserKoskeloetal.2016, author = {Niskanen, Johannes and Kooser, Kuno and Koskelo, Jaakko and K{\"a}{\"a}mbre, Tanel and Kunnus, Kristjan and Pietzsch, Annette and Quevedo, Wilson and Hakala, Mikko and F{\"o}hlisch, Alexander and Huotari, Simo and Kukk, Edwin}, title = {Density functional simulation of resonant inelastic X-ray scattering experiments in liquids: acetonitrile}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-395133}, pages = {7}, year = {2016}, abstract = {In this paper we report an experimental and computational study of liquid acetonitrile (H3C-C[triple bond, length as m-dash]N) by resonant inelastic X-ray scattering (RIXS) at the N K-edge. The experimental spectra exhibit clear signatures of the electronic structure of the valence states at the N site and incident-beam-polarization dependence is observed as well. Moreover, we find fine structure in the quasielastic line that is assigned to finite scattering duration and nuclear relaxation. We present a simple and light-to-evaluate model for the RIXS maps and analyze the experimental data using this model combined with ab initio molecular dynamics simulations. In addition to polarization-dependence and scattering-duration effects, we pinpoint the effects of different types of chemical bonding to the RIXS spectrum and conclude that the H2C-C[double bond, length as m-dash]NH isomer, suggested in the literature, does not exist in detectable quantities. We study solution effects on the scattering spectra with simulations in liquid and in vacuum. The presented model for RIXS proved to be light enough to allow phase-space-sampling and still accurate enough for identification of transition lines in physical chemistry research by RIXS.}, language = {en} } @article{YinRajkovicVeeduetal.2015, author = {Yin, Zhong and Rajkovic, Ivan and Veedu, Sreevidya Thekku and Deinert, Sascha and Raiser, Dirk and Jain, Rohit and Fukuzawa, Hironobu and Wada, Shin-ichi and Quevedo, Wilson and Kennedy, Brian and Schreck, Simon and Pietzsch, Annette and Wernet, Philippe and Ueda, Kyoshi and F{\"o}hlisch, Alexander and Techert, Simone}, title = {Ionic solutions probed by resonant inelastic X-ray scattering}, series = {Zeitschrift f{\"u}r physikalische Chemie : international journal of research in physical chemistry and chemical physics}, volume = {229}, journal = {Zeitschrift f{\"u}r physikalische Chemie : international journal of research in physical chemistry and chemical physics}, number = {10-12}, publisher = {De Gruyter}, address = {Berlin}, issn = {0942-9352}, doi = {10.1515/zpch-2015-0610}, pages = {1855 -- 1867}, year = {2015}, abstract = {X-ray spectroscopy is a powerful tool to study the local charge distribution of chemical systems. Together with the liquid jet it becomes possible to probe chemical systems in their natural environment, the liquid phase. In this work, we present X-ray absorption (XA), X-ray emission (XE) and resonant inelastic X-ray scattering (RIXS) data of pure water and various salt solutions and show the possibilities these methods offer to elucidate the nature of ion-water interaction.}, language = {en} } @article{DeckerBornRuotsalainenetal.2021, author = {Decker, Regis and Born, Artur and Ruotsalainen, Kari and Bauer, Karl and Haverkamp, Robert and B{\"u}chner, Robby and Pietzsch, Annette and F{\"o}hlisch, Alexander}, title = {Spin-lattice angular momentum transfer of localized and valence electrons in the demagnetization transient state of gadolinium}, series = {Applied physics letters}, volume = {119}, journal = {Applied physics letters}, number = {15}, publisher = {AIP Publishing}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/5.0063404}, pages = {5}, year = {2021}, abstract = {The electron-phonon scattering is one of the main microscopic mechanisms responsible for the spin-flip in the transient state of ultrafast demagnetization. Here, we present an experimental determination of the temperature-dependent electron-phonon scattering rate in Gd. Using a static x-ray emission spectroscopy method, where the reduction of the decay peak intensities when increasing the temperature is quantified, we measure independently the electron-phonon scattering rate for the 5d and the 4f electrons. We deduce the temperature dependence of scattering for the 5d electrons, while no effect on the phonon population is observed for the 4f electrons. Our results suggest that the ultrafast magnetization dynamics in Gd is triggered by the spin-flip in the 5d electrons. We also evidence the existence of a temperature threshold, above which spin-flip scattering of the 5d electrons takes place. We deduce that during the transient state of ultrafast demagnetization, the exchange energy between 5d electrons has to be overcome before the microscopic electron-phonon scattering process can occur.}, language = {en} } @misc{KubinGuoKrolletal.2018, author = {Kubin, Markus and Guo, Meiyuan and Kroll, Thomas and L{\"o}chel, Heike and K{\"a}llman, Erik and Baker, Michael L. and Mitzner, Rolf and Gul, Sheraz and Kern, Jan and F{\"o}hlisch, Alexander and Erko, Alexei and Bergmann, Uwe and Yachandra, Vittal and Yano, Junko and Lundberg, Marcus and Wernet, Philippe}, title = {Probing the oxidation state of transition metal complexes}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {656}, issn = {1866-8372}, doi = {10.25932/publishup-42505}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-425057}, pages = {17}, year = {2018}, abstract = {Transition metals in inorganic systems and metalloproteins can occur in different oxidation states, which makes them ideal redox-active catalysts. To gain a mechanistic understanding of the catalytic reactions, knowledge of the oxidation state of the active metals, ideally in operando, is therefore critical. L-edge X-ray absorption spectroscopy (XAS) is a powerful technique that is frequently used to infer the oxidation state via a distinct blue shift of L-edge absorption energies with increasing oxidation state. A unified description accounting for quantum-chemical notions whereupon oxidation does not occur locally on the metal but on the whole molecule and the basic understanding that L-edge XAS probes the electronic structure locally at the metal has been missing to date. Here we quantify how charge and spin densities change at the metal and throughout the molecule for both redox and core-excitation processes. We explain the origin of the L-edge XAS shift between the high-spin complexes Mn-II(acac)(2) and Mn-III(acac)(3) as representative model systems and use ab initio theory to uncouple effects of oxidation-state changes from geometric effects. The shift reflects an increased electron affinity of Mn-III in the core-excited states compared to the ground state due to a contraction of the Mn 3d shell upon core-excitation with accompanied changes in the classical Coulomb interactions. This new picture quantifies how the metal-centered core hole probes changes in formal oxidation state and encloses and substantiates earlier explanations. The approach is broadly applicable to mechanistic studies of redox-catalytic reactions in molecular systems where charge and spin localization/delocalization determine reaction pathways.}, language = {en} } @article{PietzschSunHenniesetal.2011, author = {Pietzsch, Annette and Sun, Y. -P. and Hennies, Franz and Rinkevicius, Z. and Karlsson, Hans O. and Schmitt, Thorsten and Strocov, Vladimir N. and Andersson, Joakim and Kennedy, B. and Schlappa, J. and F{\"o}hlisch, Alexander and Rubensson, Jan-Erik and Gel'mukhanov, F.}, title = {Spatial quantum beats in vibrational resonant inelastic soft X-ray scattering at dissociating states in oxygen}, series = {Physical review letters}, volume = {106}, journal = {Physical review letters}, number = {15}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.106.153004}, pages = {4}, year = {2011}, abstract = {Resonant inelastic soft x-ray scattering (RIXS) spectra excited at the 1 sigma(g) -> 3 sigma(u) resonance in gas-phase O-2 show excitations due to the nuclear degrees of freedom with up to 35 well-resolved discrete vibronic states and a continuum due to the kinetic energy distribution of the separated atoms. The RIXS profile demonstrates spatial quantum beats caused by two interfering wave packets with different momenta as the atoms separate. Thomson scattering strongly affects both the spectral profile and the scattering anisotropy.}, language = {en} } @article{PietzschHenniesMiedemaetal.2015, author = {Pietzsch, Annette and Hennies, Franz and Miedema, Piter S. and Kennedy, Brian and Schlappa, Justine and Schmitt, Thorsten and Strocov, Vladimir N. and F{\"o}hlisch, Alexander}, title = {Snapshots of the Fluctuating Hydrogen Bond Network in Liquid Water on the Sub-Femtosecond Timescale with Vibrational Resonant Inelastic x-ray Scattering}, series = {Physical review letters}, volume = {114}, journal = {Physical review letters}, number = {8}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.114.088302}, pages = {5}, year = {2015}, abstract = {Liquid water molecules interact strongly with each other, forming a fluctuating hydrogen bond network and thereby giving rise to the anomalous phase diagram of liquid water. Consequently, symmetric and asymmetric water molecules have been found in the picosecond time average with IR and optical Raman spectroscopy. With subnatural linewidth resonant inelastic x-ray scattering (RIXS) at vibrational resolution, we take sub-femtosecond snapshots of the electronic and structural properties of water molecules in the hydrogen bond network. We derive a strong dominance of nonsymmetric molecules in liquid water in contrast to the gas phase on the sub-femtosecond timescale of RIXS and determine the fraction of highly asymmetrically distorted molecules.}, language = {en} } @article{KubinKernGuletal.2017, author = {Kubin, Markus and Kern, Jan and Gul, Sheraz and Kroll, Thomas and Chatterjee, Ruchira and Loechel, Heike and Fuller, Franklin D. and Sierra, Raymond G. and Quevedo, Wilson and Weniger, Christian and Rehanek, Jens and Firsov, Anatoly and Laksmono, Hartawan and Weninger, Clemens and Alonso-Mori, Roberto and Nordlund, Dennis L. and Lassalle-Kaiser, Benedikt and Glownia, James M. and Krzywinski, Jacek and Moeller, Stefan and Turner, Joshua J. and Minitti, Michael P. and Dakovski, Georgi L. and Koroidov, Sergey and Kawde, Anurag and Kanady, Jacob S. and Tsui, Emily Y. and Suseno, Sandy and Han, Zhiji and Hill, Ethan and Taguchi, Taketo and Borovik, Andrew S. and Agapie, Theodor and Messinger, Johannes and Erko, Alexei and F{\"o}hlisch, Alexander and Bergmann, Uwe and Mitzner, Rolf and Yachandra, Vittal K. and Yano, Junko and Wernet, Philippe}, title = {Soft x-ray absorption spectroscopy of metalloproteins and high-valent metal-complexes at room temperature using free-electron lasers}, series = {Structural dynamics}, volume = {4}, journal = {Structural dynamics}, publisher = {American Institute of Physics}, address = {Melville}, issn = {2329-7778}, doi = {10.1063/1.4986627}, pages = {16}, year = {2017}, abstract = {X-ray absorption spectroscopy at the L-edge of 3d transition metals provides unique information on the local metal charge and spin states by directly probing 3d-derived molecular orbitals through 2p-3d transitions. However, this soft x-ray technique has been rarely used at synchrotron facilities for mechanistic studies of metalloenzymes due to the difficulties of x-ray-induced sample damage and strong background signals from light elements that can dominate the low metal signal. Here, we combine femtosecond soft x-ray pulses from a free-electron laser with a novel x-ray fluorescence-yield spectrometer to overcome these difficulties. We present L-edge absorption spectra of inorganic high-valent Mn complexes (Mn similar to 6-15 mmol/l) with no visible effects of radiation damage. We also present the first L-edge absorption spectra of the oxygen evolving complex (Mn4CaO5) in Photosystem II (Mn < 1 mmol/l) at room temperature, measured under similar conditions. Our approach opens new ways to study metalloenzymes under functional conditions. (C) 2017 Author(s).}, language = {en} } @article{LiuRuotsalainenBaueretal.2022, author = {Liu, Chun-Yu and Ruotsalainen, Kari and Bauer, Karl and Decker, R{\´e}gis and Pietzsch, Annette and F{\"o}hlisch, Alexander}, title = {Excited-state exchange interaction in NiO determined by high-resolution resonant inelastic x-ray scattering at the Ni M2,3 edges}, series = {Physical review : B, Condensed matter and materials physics}, volume = {106}, journal = {Physical review : B, Condensed matter and materials physics}, number = {3}, publisher = {American Physical Society}, address = {Ridge, NY}, issn = {2469-9950}, doi = {10.1103/PhysRevB.106.035104}, pages = {7}, year = {2022}, abstract = {The electronic and magnetic excitations of bulk NiO have been determined using the 3A2g to 3T2g crystal-field transition at the Ni M2,3 edges with resonant inelastic x-ray scattering at 66.3- and 67.9-eV photon energies and 33-meV spectral resolution. Unambiguous assignment of the high-energy side of this state to a spin-flip satellite is achieved. We extract an effective exchange field of 89±4 meV in the 3T2g excited final state from empirical two-peak spin-flip model. The experimental data is found consistent with crystal-field model calculations using exchange fields of 60-100 meV. Full agreement with crystal-field multiplet calculations is achieved for the incident photon energy dependence of line shapes. The lower exchange parameter in the excited state as compared to the ground-state value of 120 meV is discussed in terms of the modification of the orbital occupancy (electronic effects) and of the structural dynamics: (A) With pure electronic effects, the lower exchange energy is attributed to the reduction in effective hopping integral. (B) With no electronic effects, we use the S = 1 Heisenberg model of antiferromagnetism to derive a second-nearest-neighbor exchange constant J2 = 14.8±0.6 meV. Based on the linear correlation between J2 and the lattice parameter from pressure-dependent experiments, an upper limit of 2\% local Ni-O bond elongation during the femtosecond scattering duration is derived.}, language = {en} } @article{BornDeckerHaverkampetal.2021, author = {Born, Artur and Decker, Regis and Haverkamp, Robert and Ruotsalainen, Kari and Bauer, Karl and Pietzsch, Annette and F{\"o}hlisch, Alexander and B{\"u}chner, Robby}, title = {Thresholding of the Elliott-Yafet spin-flip scattering in multi-sublattice magnets by the respective exchange energies}, series = {Scientific reports}, volume = {11}, journal = {Scientific reports}, number = {1}, publisher = {Springer Nature}, address = {Berlin}, issn = {2045-2322}, doi = {10.1038/s41598-021-81177-9}, pages = {7}, year = {2021}, abstract = {How different microscopic mechanisms of ultrafast spin dynamics coexist and interplay is not only relevant for the development of spintronics but also for the thorough description of physical systems out-of-equilibrium. In pure crystalline ferromagnets, one of the main microscopic mechanism of spin relaxation is the electron-phonon (el-ph) driven spin-flip, or Elliott-Yafet, scattering. Unexpectedly, recent experiments with ferro- and ferrimagnetic alloys have shown different dynamics for the different sublattices. These distinct sublattice dynamics are contradictory to the Elliott-Yafet scenario. In order to rationalize this discrepancy, it has been proposed that the intra- and intersublattice exchange interaction energies must be considered in the microscopic demagnetization mechanism, too. Here, using a temperature-dependent x-ray emission spectroscopy (XES) method, we address experimentally the element specific el-ph angular momentum transfer rates, responsible for the spin-flips in the respective (sub)lattices of Fe20Ni80, Fe50Ni50 and pure nickel single crystals. We establish how the deduced rate evolution with the temperature is linked to the exchange coupling constants reported for different alloy stoichiometries and how sublattice exchange energies threshold the related el-ph spin-flip channels. Thus, these results evidence that the Elliott-Yafet spin-flip scattering, thresholded by sublattice exchange energies, is the relevant microscopic process to describe sublattice dynamics in alloys and elemental magnetic systems.}, language = {en} } @article{ArhammarPietzschBocketal.2011, author = {Arhammar, C. and Pietzsch, Annette and Bock, Nicolas and Holmstroem, Erik and Araujo, C. Moyses and Grasjo, Johan and Zhao, Shuxi and Green, Sara and Peery, T. and Hennies, Franz and Amerioun, Shahrad and F{\"o}hlisch, Alexander and Schlappa, Justine and Schmitt, Thorsten and Strocov, Vladimir N. and Niklasson, Gunnar A. and Wallace, Duane C. and Rubensson, Jan-Erik and Johansson, Borje and Ahuja, Rajeev C.}, title = {Unveiling the complex electronic structure of amorphous metal oxides}, series = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {108}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, number = {16}, publisher = {National Acad. of Sciences}, address = {Washington}, issn = {0027-8424}, doi = {10.1073/pnas.1019698108}, pages = {6355 -- 6360}, year = {2011}, abstract = {Amorphous materials represent a large and important emerging area of material's science. Amorphous oxides are key technological oxides in applications such as a gate dielectric in Complementary metal-oxide semiconductor devices and in Silicon-Oxide-Nitride-Oxide-Silicon and TANOS (TaN-Al2O3-Si3N4-SiO2-Silicon) flash memories. These technologies are required for the high packing density of today's integrated circuits. Therefore the investigation of defect states in these structures is crucial. In this work we present X-ray synchrotron measurements, with an energy resolution which is about 5-10 times higher than is attainable with standard spectrometers, of amorphous alumina. We demonstrate that our experimental results are in agreement with calculated spectra of amorphous alumina which we have generated by stochastic quenching. This first principles method, which we have recently developed, is found to be superior to molecular dynamics in simulating the rapid gas to solid transition that takes place as this material is deposited for thin film applications. We detect and analyze in detail states in the band gap that originate from oxygen pairs. Similar states were previously found in amorphous alumina by other spectroscopic methods and were assigned to oxygen vacancies claimed to act mutually as electron and hole traps. The oxygen pairs which we probe in this work act as hole traps only and will influence the information retention in electronic devices. In amorphous silica oxygen pairs have already been found, thus they may be a feature which is characteristic also of other amorphous metal oxides.}, language = {en} } @article{SunMiaoPietzschetal.2013, author = {Sun, Y. -P. and Miao, Q. and Pietzsch, Annette and Hennies, F. and Schmitt, T. and Strocov, V. N. and Andersson, Joakim and Kennedy, B. and Schlappa, J. and F{\"o}hlisch, Alexander and Gel\&rsquo, and mukhanov, F. and Rubensson, J. -E.}, title = {Interference between Resonant and Nonresonant Inelastic X-Ray Scattering}, series = {PHYSICAL REVIEW LETTERS}, volume = {110}, journal = {PHYSICAL REVIEW LETTERS}, number = {22}, publisher = {AMER PHYSICAL SOC}, address = {COLLEGE PK}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.110.223001}, pages = {4}, year = {2013}, abstract = {A detailed study of inelastic x-ray scattering from the ground state to the (3)Sigma(g)(3 sigma(-1)(g)3s(g)(1)) state of the O-2 molecule is presented. The observed angular anisotropy shows that the vibrational excitations within this final state are strongly dependent on the polarization of the incident radiation. The analysis demonstrates that this is a manifestation of interference between resonant and direct nonresonant inelastic x-ray scattering. This interference provides a new tool to monitor nuclear dynamics by relative rotation of the polarization vectors of the incident and scattered photons.}, language = {en} } @article{SunPietzschHenniesetal.2011, author = {Sun, Y-P and Pietzsch, Annette and Hennies, Franz and Rinkevicius, Z. and Karlsson, Hans O. and Schmitt, Thorsten and Strocov, Vladimir N. and Andersson, Joakim and Kennedy, B. and Schlappa, J. and F{\"o}hlisch, Alexander and Gel'mukhanov, F. and Rubensson, Jan-Erik}, title = {Internal symmetry and selection rules in resonant inelastic soft x-ray scattering}, series = {Journal of physics : B, Atomic, molecular and optical physics}, volume = {44}, journal = {Journal of physics : B, Atomic, molecular and optical physics}, number = {16}, publisher = {IOP Publ. Ltd.}, address = {Bristol}, issn = {0953-4075}, doi = {10.1088/0953-4075/44/16/161002}, pages = {5}, year = {2011}, abstract = {Resonant inelastic soft x-ray scattering spectra excited at the dissociative 1 sigma(g) -> 3 sigma(u) resonance in gas-phase O(2) are presented and discussed in terms of state-of-the-art molecular theory. A new selection rule due to internal spin coupling is established, facilitating a deep analysis of the valence excited final states. Furthermore, it is found that a commonly accepted symmetry selection rule due to orbital parity breaks down, as the core hole and excited electron swap parity, thereby opening the symmetry forbidden 3 sigma(g) decay channel.}, language = {en} } @article{HenniesPietzschBerglundetal.2010, author = {Hennies, Franz and Pietzsch, Annette and Berglund, Martin and F{\"o}hlisch, Alexander and Schmitt, Thorsten and Strocov, Vladimir and Karlsson, Hans O. and Andersson, Joakim and Rubensson, Jan-Erik}, title = {Resonant inelastic scattering spectra of free molecules with vibrational resolution}, issn = {0031-9007}, doi = {10.1103/Physrevlett.104.193002}, year = {2010}, abstract = {Inelastic x-ray scattering spectra excited at the 1s(-1) pi* resonance of gas phase O-2 have been recorded with an overall energy resolution that allows for well-resolved vibrational progressions. The nuclear wave packet dynamics in the intermediate state is reflected in vibrational excitations of the electronic ground state, and by fine-tuning the excitation energy the dissociation dynamics in the predissociative B' (3) Pi(g) final state is controlled.}, language = {en} } @article{SchreckPietzschKunnusetal.2014, author = {Schreck, Simon and Pietzsch, Annette and Kunnus, Kristjan and Kennedy, Brian and Quevedo, Wilson and Miedema, Piter S. and Wernet, Philippe and F{\"o}hlisch, Alexander}, title = {Dynamics of the OH group and the electronic structure of liquid alcohols}, series = {Structural dynamics}, volume = {1}, journal = {Structural dynamics}, number = {5}, publisher = {American Institute of Physics}, address = {Melville}, issn = {2329-7778}, doi = {10.1063/1.4897981}, pages = {14}, year = {2014}, abstract = {In resonant inelastic soft x-ray scattering (RIXS) from molecular and liquid systems, the interplay of ground state structural and core-excited state dynamical contributions leads to complex spectral shapes that partially allow for ambiguous interpretations. In this work, we dissect these contributions in oxygen K-edge RIXS from liquid alcohols. We use the scattering into the electronic ground state as an accurate measure of nuclear dynamics in the intermediate core-excited state of the RIXS process. We determine the characteristic time in the core-excited state until nuclear dynamics give a measurable contribution to the RIXS spectral profiles to tau(dyn) = 1.2 +/- 0.8 fs. By detuning the excitation energy below the absorption resonance we reduce the effective scattering time below sdyn, and hence suppress these dynamical contributions to a minimum. From the corresponding RIXS spectra of liquid methanol, we retrieve the "dynamic-free" density of states and find that it is described solely by the electronic states of the free methanol molecule. From this and from the comparison of normal and deuterated methanol, we conclude that the split peak structure found in the lone-pair emission region at non-resonant excitation originates from dynamics in the O-H bond in the core-excited state. We find no evidence that this split peak feature is a signature of distinct ground state structural complexes in liquid methanol. However, we demonstrate how changes in the hydrogen bond coordination within the series of linear alcohols from methanol to hexanol affect the split peak structure in the liquid alcohols. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.}, language = {en} } @article{SchickLeGuyaderPontiusetal.2016, author = {Schick, Daniel and Le Guyader, Loic and Pontius, Niko and Radu, Ilie and Kachel, Torsten and Mitzner, Rolf and Zeschke, Thomas and Schuessler-Langeheine, Christian and F{\"o}hlisch, Alexander and Holldack, Karsten}, title = {Analysis of the halo background in femtosecond slicing experiments}, series = {Journal of synchrotron radiation}, volume = {23}, journal = {Journal of synchrotron radiation}, publisher = {International Union of Crystallography}, address = {Chester}, issn = {1600-5775}, doi = {10.1107/S160057751600401X}, pages = {700 -- 711}, year = {2016}, abstract = {The slicing facility FemtoSpeX at BESSY II offers unique opportunities to study photo-induced dynamics on femtosecond time scales by means of X-ray magnetic circular dichroism, resonant and non-resonant X-ray diffraction, and X-ray absorption spectroscopy experiments in the soft X-ray regime. Besides femtosecond X-ray pulses, slicing sources inherently also produce a so-called `halo' background with a different time structure, polarization and pointing. Here a detailed experimental characterization of the halo radiation is presented, and a method is demonstrated for its correct and unambiguous removal from femtosecond time-resolved data using a special laser triggering scheme as well as analytical models. Examples are given for time-resolved measurements with corresponding halo correction, and errors of the relevant physical quantities caused by either neglecting or by applying a simplified model to describe this background are estimated.}, language = {en} } @article{RubenssonSoderstromBinggelietal.2015, author = {Rubensson, Jan-Erik and Soderstrom, Johan and Binggeli, Christian and Grasjo, Joakim and Andersson, Johan and Sathe, Conny and Hennies, Franz and Bisogni, Valentina and Huang, Yaobo and Olalde, Paul and Schmitt, Thorsten and Strocov, Vladimir N. and F{\"o}hlisch, Alexander and Kennedy, Brian and Pietzsch, Annette}, title = {Rydberg-Resolved Resonant Inelastic Soft X-Ray Scattering: Dynamics at Core Ionization Thresholds}, series = {Physical review letters}, volume = {114}, journal = {Physical review letters}, number = {13}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.114.133001}, pages = {5}, year = {2015}, abstract = {Resonant inelastic x-ray scattering spectra excited in the immediate vicinity of the core-level ionization thresholds of N-2 have been recorded. Final states of well-resolved symmetry-selected Rydberg series converging to valence-level ionization thresholds with vibrational excitations are observed. The results are well described by a quasi-two-step model which assumes that the excited electron is unaffected by the radiative decay. This threshold dynamics simplifies the interpretation of resonant inelastic x-ray scattering spectra considerably and facilitates characterization of low-energy excited final states in molecular systems.}, language = {en} } @article{YinRajkovicKubiceketal.2014, author = {Yin, Zhong and Rajkovic, Ivan and Kubicek, Katharina and Quevedo, Wilson and Pietzsch, Annette and Wernet, Philippe and F{\"o}hlisch, Alexander and Techert, Simone}, title = {Probing the Hofmeister effect with ultrafast core-hole spectroscopy}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {118}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, number = {31}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/jp504577a}, pages = {9398 -- 9403}, year = {2014}, abstract = {In the current work, X-ray emission spectra of aqueous solutions of different inorganic salts within the Hofmeister series are presented. The results reflect the direct interaction of the ions with the water molecules and therefore, reveal general properties of the salt-water interactions. Within the experimental precision a significant effect of the ions on the water structure has been observed but no ordering according to the structure maker/structure breaker concept could be mirrored in the results indicating that the Hofmeister effect if existent may be caused by more complex interactions.}, language = {en} } @misc{EschenlohrBattiatoMaldonadoetal.2014, author = {Eschenlohr, Andrea and Battiato, Mario and Maldonado, P. and Pontius, N. and Kachel, T. and Holldack, K. and Mitzner, Rolf and F{\"o}hlisch, Alexander and Oppeneer, P. M. and Stamm, Christian}, title = {Optical excitation of thin magnetic layers in multilayer structures Reply}, series = {Nature materials}, volume = {13}, journal = {Nature materials}, number = {2}, publisher = {Nature Publ. Group}, address = {London}, issn = {1476-1122}, doi = {10.1038/nmat3851}, pages = {102 -- 103}, year = {2014}, language = {en} } @article{YinInhesterVeeduetal.2017, author = {Yin, Zhong and Inhester, Ludger and Veedu, Sreevidya Thekku and Quevedo, Wilson and Pietzsch, Annette and Wernet, Philippe and Groenhof, Gerrit and F{\"o}hlisch, Alexander and Grubmueller, Helmut and Techert, Simone}, title = {Cationic and Anionic Impact on the Electronic Structure of Liquid Water}, series = {The journal of physical chemistry letters}, volume = {8}, journal = {The journal of physical chemistry letters}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/acs.jpclett.7b01392}, pages = {3759 -- 3764}, year = {2017}, abstract = {Hydration shells around ions are crucial for many fundamental biological and chemical processes. Their local physicochemical properties are quite different from those of bulk water and hard to probe experimentally. We address this problem by combining soft X-ray spectroscopy using a liquid jet and molecular dynamics (MD) simulations together with ab initio electronic structure calculations to elucidate the water ion interaction in a MgCl2 solution at the molecular level. Our results reveal that salt ions mainly affect the electronic properties of water molecules in close vicinity and that the oxygen K-edge X-ray emission spectrum of water molecules in the first solvation shell differs significantly from that of bulk water. Ion-specific effects are identified by fingerprint features in the water X-ray emission spectra. While Mg2+ ions cause a bathochromic shift of the water lone pair orbital, the 3p orbital of the Cl- ions causes an additional peak in the water emission spectrum at around 528 eV.}, language = {en} } @article{SchreckPietzschKennedyetal.2016, author = {Schreck, Simon and Pietzsch, Annette and Kennedy, Brian and Sathe, Conny and Miedema, Piter S. and Techert, Simone and Strocov, Vladimir N. and Schmitt, Thorsten and Hennies, Franz and Rubensson, Jan-Erik and F{\"o}hlisch, Alexander}, title = {Ground state potential energy surfaces around selected atoms from resonant inelastic x-ray scattering}, series = {Scientific reports}, volume = {6}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/srep20054}, pages = {7}, year = {2016}, abstract = {Thermally driven chemistry as well as materials' functionality are determined by the potential energy surface of a systems electronic ground state. This makes the potential energy surface a central and powerful concept in physics, chemistry and materials science. However, direct experimental access to the potential energy surface locally around atomic centers and to its long-range structure are lacking. Here we demonstrate how sub-natural linewidth resonant inelastic soft x-ray scattering at vibrational resolution is utilized to determine ground state potential energy surfaces locally and detect long-range changes of the potentials that are driven by local modifications. We show how the general concept is applicable not only to small isolated molecules such as O2 but also to strongly interacting systems such as the hydrogen bond network in liquid water. The weak perturbation to the potential energy surface through hydrogen bonding is observed as a trend towards softening of the ground state potential around the coordinating atom. The instrumental developments in high resolution resonant inelastic soft x-ray scattering are currently accelerating and will enable broad application of the presented approach. With this multidimensional potential energy surfaces that characterize collective phenomena such as (bio)molecular function or high-temperature superconductivity will become accessible in near future.}, language = {en} } @article{ThielemannKuehnSchickPontiusetal.2017, author = {Thielemann-K{\"u}hn, Nele and Schick, Daniel and Pontius, Niko and Trabant, Christoph and Mitzner, Rolf and Holldack, Karsten and Zabel, Hartmut and F{\"o}hlisch, Alexander and Schuessler-Langeheine, Christian}, title = {Ultrafast and Energy-Efficient Quenching of Spin Order: Antiferromagnetism Beats Ferromagnetism}, series = {Physical review letters}, volume = {119}, journal = {Physical review letters}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.119.197202}, pages = {6}, year = {2017}, abstract = {By comparing femtosecond laser pulse induced ferro- and antiferromagnetic dynamics in one and the same material-metallic dysprosium-we show both to behave fundamentally different. Antiferromagnetic order is considerably faster and much more efficiently reduced by optical excitation than its ferromagnetic counterpart. We assign the fast and extremely efficient process in the antiferromagnet to an interatomic transfer of angular momentum within the spin system. Our findings imply that this angular momentum transfer channel is effective in other magnetic metals with nonparallel spin alignment. They also point out a possible route towards energy-efficient spin manipulation for magnetic devices.}, language = {en} } @article{MiedemaMitznerGanschowetal.2017, author = {Miedema, P. S. and Mitzner, Rolf and Ganschow, S. and F{\"o}hlisch, Alexander and Beye, Martin}, title = {X-ray spectroscopy on the active ion in laser crystals}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {19}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c7cp03026f}, pages = {21800 -- 21806}, year = {2017}, abstract = {The active ions in typical laser crystals were studied with Resonant Inelastic X-ray Scattering (RIXS) and Partial Fluorescence Yield X-ray Absorption (PFY-XAS) spectroscopies as solid state model systems for dilute active centers. We analyzed Ti3+ and Cr3+ in alpha-Al2O3:Ti3+ and LiCaAlF6:Cr3+, respectively. The comparison of experimental data with semi-empirical multiplet calculations provides insights into the electronic structure and shows how measured crystal field energies are related across different spectroscopies.}, language = {en} } @article{DeckerBornBuechneretal.2019, author = {Decker, R{\´e}gis and Born, Artur and B{\"u}chner, Robby and Ruotsalainen, Kari and Str{\aa}hlman, Christian and Neppl, Stefan and Haverkamp, Robert and Pietzsch, Annette and F{\"o}hlisch, Alexander}, title = {Measuring the atomic spin-flip scattering rate by x-ray emission spectroscopy}, series = {Scientific reports}, volume = {9}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/s41598-019-45242-8}, pages = {6}, year = {2019}, abstract = {While extensive work has been dedicated to the measurement of the demagnetization time following an ultra-short laser pulse, experimental studies of its underlying microscopic mechanisms are still scarce. In transition metal ferromagnets, one of the main mechanism is the spin-flip of conduction electrons driven by electron-phonon scattering. Here, we present an original experimental method to monitor the electron-phonon mediated spin-flip scattering rate in nickel through the stringent atomic symmetry selection rules of x-ray emission spectroscopy. Increasing the phonon population leads to a waning of the 3d -> 2p(3/2) decay peak intensity, which reflects an increase of the angular momentum transfer scattering rate attributed to spin-flip. We find a spin relaxation time scale in the order of 50 fs in the 3d-band of nickel at room temperature, while consistantly, no such peak evolution is observed for the diamagnetic counterexample copper, using the same method.}, language = {en} } @article{LiuVazdaCruzPolyutovetal.2019, author = {Liu, Ji-Cai and Vaz da Cruz, Vinicius and Polyutov, Sergey and F{\"o}hlisch, Alexander}, title = {Recoil-induced dissociation in hard-x-ray photoionization}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {100}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9926}, doi = {10.1103/PhysRevA.100.053408}, pages = {7}, year = {2019}, abstract = {We predict the recoil-induced molecular dissociation in hard-x-ray photoionization. The recoil effect is caused by electronic and photon momentum exchange with the molecule. We show the strong role of relativistic effects for the studied molecular fragmentation. The recoil-induced fragmentation of the molecule is caused by elongation of the bond due to the vibrational recoil effect and because of the centrifugal force caused by the rotational recoil. The calculations of the x-ray photoelectron spectra of the H-2 and NO molecules show that the predicted effects can be observed in high-energy synchrotrons like SOLEIL, SPring-8, PETRA, and XFEL SACLA. The relativistic effect enhances the recoil momentum transfer and makes it strongly sensitive to the direction of ejection of the fast photoelectron with respect to the photon momentum.}, language = {en} } @article{BuechnerFondellMascarenhasetal.2021, author = {B{\"u}chner, Robby and Fondell, Mattis and Mascarenhas, Eric Johnn and Pietzsch, Annette and Vaz da Cruz, Vin{\´i}cius and F{\"o}hlisch, Alexander}, title = {How hydrogen bonding amplifies isomeric differences in pyridones toward strong changes in acidity and tautomerism}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {125}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, number = {9}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.0c10873}, pages = {2372 -- 2379}, year = {2021}, abstract = {Steric hindrance of hydration and hydrogen bond enhancement by localized charges have been identified as key factors for the massive chemical differences between the hydroxypyridine/pyridone isomers in aqueous solution. While all isomers occur mainly in the hydroxypyridine form in the gas phase, they differ by more than 3 orders of magnitude both in their acidity and tautomeric equilibrium constants upon hydration. By monitoring the electronic and solvation structures as a function of the protonation state and the O- substitution position on the pyridine ring, the amplification of the isomeric differences in aqueous solution has been investigated. Near-edge X-ray absorption fine structure (NEXAFS) measurements at the N K-edge served as the probe of the chemical state. The combination of molecular dynamics simulations, complete active space self-consistent field (CASSCF), and time-dependent density functional theory (TD-DFT) spectral calculations contributes to unraveling the principles of tautomerism and acidity in multiple biochemical systems based on tautomerism.}, language = {en} } @article{BuechnerFondellHaverkampetal.2021, author = {B{\"u}chner, Robby and Fondell, Mattis and Haverkamp, Robert and Pietzsch, Annette and Vaz da Cruz, Vin{\´i}cius and F{\"o}hlisch, Alexander}, title = {The porphyrin center as a regulator for metal-ligand covalency and pi hybridization in the entire molecule}, series = {Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies}, volume = {23}, journal = {Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies}, number = {43}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/d1cp03944j}, pages = {24765 -- 24772}, year = {2021}, abstract = {The central moiety of porphyrins is shown to control the charge state of the inner complex and links it by covalent interaction to the peripheral substituents. This link, which enables the versatile functions of porphyrins, is not picked up in the established, reduced four orbital picture [Gouterman, J. Mol. Spectrosc., 1961, 6, 138]. X-ray absorption spectroscopy at the N K-edge with density functional theory approaches gives access to the full electronic structure, in particular the pi* manifold beyond the Gouterman orbitals. Systematic variation of the central moiety highlights two linked, governing trends: The ionicity of the porphyrin center increases from the aminic N-H to N-Cu to N-Zn to N-Mg to the iminic N:. At the same time covalency with peripheral substituents increases and compensates the buildup of high charge density at the coordinated nitrogen sites.}, language = {en} } @article{EckertVazdaCruzOchmannetal.2021, author = {Eckert, Sebastian and Vaz da Cruz, Vin{\´i}cius and Ochmann, Miguel and Ahnen, Inga von and F{\"o}hlisch, Alexander and Huse, Nils}, title = {Breaking the symmetry of pyrimidine}, series = {The journal of physical chemistry letters}, volume = {12}, journal = {The journal of physical chemistry letters}, number = {35}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/acs.jpclett.1c01865}, pages = {8637 -- 8643}, year = {2021}, abstract = {Symmetry and its breaking crucially define the chemical properties of molecules and their functionality. Resonant inelastic X-ray scattering is a local electronic structure probe reporting on molecular symmetry and its dynamical breaking within the femtosecond scattering duration. Here, we study pyrimidine, a system from the C-2v point group, in an aqueous solution environment, using scattering though its 2a(2) resonance. Despite the absence of clean parity selection rules for decay transitions from in-plane orbitals, scattering channels including decay from the 7b(2) and 11a(1) orbitals with nitrogen lone pair character are a direct probe for molecular symmetry. Computed spectra of explicitly solvated molecules sampled from a molecular dynamics simulation are combined with the results of a quantum dynamical description of the X-ray scattering process. We observe dominant signatures of core-excited Jahn-Teller induced symmetry breaking for resonant excitation. Solvent contributions are separable by shortening of the effective scattering duration through excitation energy detuning.}, language = {en} } @article{SellbergMcQueenLaksmonoetal.2015, author = {Sellberg, Jonas A. and McQueen, Trevor A. and Laksmono, Hartawan and Schreck, Simon and Beye, Martin and DePonte, Daniel P. and Kennedy, Brian and Nordlund, Dennis and Sierra, Raymond G. and Schlesinger, Daniel and Tokushima, Takashi and Zhovtobriukh, Iurii and Eckert, Sebastian and Segtnan, Vegard H. and Ogasawara, Hirohito and Kubicek, Katharina and Techert, Simone and Bergmann, Uwe and Dakovski, Georgi L. and Schlotter, William F. and Harada, Yoshihisa and Bogan, Michael J. and Wernet, Philippe and F{\"o}hlisch, Alexander and Pettersson, Lars G. M. and Nilsson, Anders}, title = {X-ray emission spectroscopy of bulk liquid water in "no-man's land"}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {142}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {4}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.4905603}, pages = {9}, year = {2015}, abstract = {The structure of bulk liquid water was recently probed by x-ray scattering below the temperature limit of homogeneous nucleation (T-H) of similar to 232 K [J. A. Sellberg et al., Nature 510, 381-384 (2014)]. Here, we utilize a similar approach to study the structure of bulk liquid water below T-H using oxygen K-edge x-ray emission spectroscopy (XES). Based on previous XES experiments [T. Tokushima et al., Chem. Phys. Lett. 460, 387-400 (2008)] at higher temperatures, we expected the ratio of the 1b(1)' and 1b(1)" peaks associated with the lone-pair orbital in water to change strongly upon deep supercooling as the coordination of the hydrogen (H-) bonds becomes tetrahedral. In contrast, we observed only minor changes in the lone-pair spectral region, challenging an interpretation in terms of two interconverting species. A number of alternative hypotheses to explain the results are put forward and discussed. Although the spectra can be explained by various contributions from these hypotheses, we here emphasize the interpretation that the line shape of each component changes dramatically when approaching lower temperatures, where, in particular, the peak assigned to the proposed disordered component would become more symmetrical as vibrational interference becomes more important. (C) 2015 AIP Publishing LLC.}, language = {en} } @article{KunnusRajkovicSchrecketal.2012, author = {Kunnus, Kristjan and Rajkovic, Ivan and Schreck, Simon and Quevedo, Wilson and Eckert, Sebastian and Beye, Martin and Suljoti, Edlira and Weniger, Christian and Kalus, Christian and Gruebel, Sebastian and Scholz, Mirko and Nordlund, Dennis and Zhang, Wenkai and Hartsock, Robert W. and Gaffney, Kelly J. and Schlotter, William F. and Turner, Joshua J. and Kennedy, Brian and Hennies, Franz and Techert, Simone and Wernet, Philippe and F{\"o}hlisch, Alexander}, title = {A setup for resonant inelastic soft x-ray scattering on liquids at free electron laser light sources}, series = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques}, volume = {83}, journal = {Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques}, number = {12}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0034-6748}, doi = {10.1063/1.4772685}, pages = {8}, year = {2012}, abstract = {We present a flexible and compact experimental setup that combines an in vacuum liquid jet with an x-ray emission spectrometer to enable static and femtosecond time-resolved resonant inelastic soft x-ray scattering (RIXS) measurements from liquids at free electron laser (FEL) light sources. We demonstrate the feasibility of this type of experiments with the measurements performed at the Linac Coherent Light Source FEL facility. At the FEL we observed changes in the RIXS spectra at high peak fluences which currently sets a limit to maximum attainable count rate at FELs. The setup presented here opens up new possibilities to study the structure and dynamics in liquids.}, language = {en} } @article{EckertNorellMiedemaetal.2017, author = {Eckert, Sebastian and Norell, Jesper and Miedema, Piter S. and Beye, Martin and Fondell, Mattis and Quevedo, Wilson and Kennedy, Brian and Hantschmann, Markus and Pietzsch, Annette and van Kuiken, Benjamin and Ross, Matthew and Minitti, Michael P. and Moeller, Stefan P. and Schlotter, William F. and Khalil, Munira and Odelius, Michael and F{\"o}hlisch, Alexander}, title = {Untersuchung unabh{\"a}ngiger N-H- und N-C-Bindungsverformungen auf ultrakurzen Zeitskalen mit resonanter inelastischer R{\"o}ntgenstreuung}, series = {Angewandte Chemie}, volume = {129}, journal = {Angewandte Chemie}, number = {22}, issn = {1521-3757}, doi = {10.1002/ange.201700239}, pages = {6184 -- 6188}, year = {2017}, abstract = {Die Femtosekundendynamik nach resonanten Photoanregungen mit optischen und R{\"o}ntgenpulsen erm{\"o}glicht eine selektive Verformung von chemischen N-H- und N-C-Bindungen in 2-Thiopyridon in w{\"a}ssriger L{\"o}sung. Die Untersuchung der orbitalspezifischen elektronischen Struktur und ihrer Dynamik auf ultrakurzen Zeitskalen mit resonanter inelastischer R{\"o}ntgenstreuung an der N1s-Resonanz am Synchrotron und dem Freie-Elektronen-Laser LCLS in Kombination mit quantenchemischen Multikonfigurationsberechnungen erbringen den direkten Nachweis dieser kontrollierten photoinduzierten Molek{\"u}lverformungen und ihrer ultrakurzen Zeitskala.}, language = {de} } @article{EckertNorellMiedemaetal.2017, author = {Eckert, Sebastian and Norell, Jesper and Miedema, Piter S. and Beye, Martin and Fondell, Mattis and Quevedo, Wilson and Kennedy, Brian and Hantschmann, Markus and Pietzsch, Annette and Van Kuiken, Benjamin E. and Ross, Matthew and Minitti, Michael P. and Moeller, Stefan P. and Schlotter, William F. and Khalil, Munira and Odelius, Michael and F{\"o}hlisch, Alexander}, title = {Ultrafast Independent N-H and N-C Bond Deformation Investigated with Resonant Inelastic X-Ray Scattering}, series = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, volume = {56}, journal = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1433-7851}, doi = {10.1002/anie.201700239}, pages = {6088 -- 6092}, year = {2017}, abstract = {The femtosecond excited-state dynamics following resonant photoexcitation enable the selective deformation of N-H and N-C chemical bonds in 2-thiopyridone in aqueous solution with optical or X-ray pulses. In combination with multiconfigurational quantum-chemical calculations, the orbital-specific electronic structure and its ultrafast dynamics accessed with resonant inelastic X-ray scattering at the N 1s level using synchrotron radiation and the soft X-ray free-electron laser LCLS provide direct evidence for this controlled photoinduced molecular deformation and its ultrashort time-scale.}, language = {en} } @article{VazdaCruzErtanCoutoetal.2017, author = {Vaz da Cruz, Vinicius and Ertan, Emelie and Couto, Rafael C. and Eckert, Sebastian and Fondell, Mattis and Dantz, Marcus and Kennedy, Brian and Schmitt, Thorsten and Pietzsch, Annette and Guimaraes, Freddy F. and {\AA}gren, Hans and Odelius, Michael and F{\"o}hlisch, Alexander and Kimberg, Victor}, title = {A study of the water molecule using frequency control over nuclear dynamics in resonant X-ray scattering}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {19}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c7cp01215b}, pages = {19573 -- 19589}, year = {2017}, abstract = {In this combined theoretical and experimental study we report a full analysis of the resonant inelastic X-ray scattering (RIXS) spectra of H2O, D2O and HDO. We demonstrate that electronically-elastic RIXS has an inherent capability to map the potential energy surface and to perform vibrational analysis of the electronic ground state in multimode systems. We show that the control and selection of vibrational excitation can be performed by tuning the X-ray frequency across core-excited molecular bands and that this is clearly reflected in the RIXS spectra. Using high level ab initio electronic structure and quantum nuclear wave packet calculations together with high resolution RIXS measurements, we discuss in detail the mode coupling, mode localization and anharmonicity in the studied systems.}, language = {en} } @article{NorellEckertVanKuikenetal.2019, author = {Norell, Jesper and Eckert, Sebastian and Van Kuiken, Benjamin E. and F{\"o}hlisch, Alexander and Odelius, Michael}, title = {Ab initio simulations of complementary K-edges and solvatization effects for detection of proton transfer in aqueous 2-thiopyridone}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {151}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {11}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.5109840}, pages = {12}, year = {2019}, abstract = {The nitrogen and sulfur K-edge X-ray absorption spectra of aqueous 2-thiopyridone, a model system for excited-state proton transfer in several recent time-resolved measurements, have been simulated from ab initio molecular dynamics. Spectral signatures of the local intra- and inter-molecular structure are identified and rationalized, which facilitates experimental interpretation and optimization. In particular, comparison of aqueous and gas phase spectrum simulations assesses the previously unquantified solvatization effects, where hydrogen bonding is found to yield solvatochromatic shifts up to nearly 1 eV of the main peak positions. Thereby, while each K-edge can still decisively determine the local protonation of its core-excited site, only their combined, complementary fingerprints allow separating all of the three relevant molecular forms, giving a complete picture of the proton transfer.}, language = {en} } @article{EckertNiskanenJayetal.2017, author = {Eckert, Sebastian and Niskanen, Johannes and Jay, Raphael Martin and Miedema, Piter S. and Fondell, Mattis and Kennedy, Brian and Quevedo, Wilson and Iannuzzi, Marcella and F{\"o}hlisch, Alexander}, title = {Valence orbitals and local bond dynamics around N atoms of histidine under X-ray irradiation}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {19}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c7cp05713j}, pages = {32091 -- 32098}, year = {2017}, abstract = {The valence orbitals of aqueous histidine under basic, neutral and acidic conditions and their X-ray induced transformations have been monitored through N 1s resonant inelastic X-ray scattering. Using density functional ab initio molecular dynamics simulations in the core-hole state within the Z + 1 approximation, core-excitation-induced molecular transformations are quantified. Spectroscopic evidence for a highly directional X-ray-induced local N-H dissociation within the scattering duration is presented for acidic histidine. Our report demonstrates a protonation-state and chemical-environment dependent propensity for a molecular dissociation, which is induced by the absorption of high energy photons. This case study indicates that structural deformations in biomolecules under exposure to ionizing radiation, yielding possible alteration or loss of function, is highly dependent on the physiological state of the molecule upon irradiation.}, language = {en} } @article{EckertMiedemaQuevedoetal.2016, author = {Eckert, Sebastian and Miedema, P. S. and Quevedo, W. and Fondell, Mattis and Beye, Martin and Pietzsch, Annette and Ross, M. and Khalil, M. and F{\"o}hlisch, Alexander}, title = {Molecular structures and protonation state of 2-Mercaptopyridine in aqueous solution}, series = {Chemical physics letters}, volume = {647}, journal = {Chemical physics letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0009-2614}, doi = {10.1016/j.cplett.2016.01.050}, pages = {103 -- 106}, year = {2016}, abstract = {The speciation of 2-Mercaptopyridine in aqueous solution has been investigated with nitrogen 1s Near Edge X-ray Absorption Fine Structure spectroscopy and time dependent Density Functional Theory. The prevalence of distinct species as a function of the solvent basicity is established. No indications of dimerization towards high concentrations are found. The determination of different molecular structures of 2-Mercaptopyridine in aqueous solution is put into the context of proton-transfer in keto-enol and thione-thiol tautomerisms. (C) 2016 The Authors. Published by Elsevier B.V.}, language = {en} } @article{JayNorellEckertetal.2018, author = {Jay, Raphael M. and Norell, Jesper and Eckert, Sebastian and Hantschmann, Markus and Beye, Martin and Kennedy, Brian and Quevedo, Wilson and Schlotter, William F. and Dakovski, Georgi L. and Minitti, Michael P. and Hoffmann, Matthias C. and Mitra, Ankush and Moeller, Stefan P. and Nordlund, Dennis and Zhang, Wenkai and Liang, Huiyang W. and Kunnus, Kristian and Kubicek, Katharina and Techert, Simone A. and Lundberg, Marcus and Wernet, Philippe and Gaffney, Kelly and Odelius, Michael and F{\"o}hlisch, Alexander}, title = {Disentangling Transient Charge Density and Metal-Ligand Covalency in Photoexcited Ferricyanide with Femtosecond Resonant Inelastic Soft X-ray Scattering}, series = {The journal of physical chemistry letters}, volume = {9}, journal = {The journal of physical chemistry letters}, number = {12}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/acs.jpclett.8b01429}, pages = {3538 -- 3543}, year = {2018}, abstract = {Soft X-ray spectroscopies are ideal probes of the local valence electronic structure of photocatalytically active metal sites. Here, we apply the selectivity of time resolved resonant inelastic X-ray scattering at the iron L-edge to the transient charge distribution of an optically excited charge-transfer state in aqueous ferricyanide. Through comparison to steady-state spectra and quantum chemical calculations, the coupled effects of valence-shell closing and ligand-hole creation are experimentally and theoretically disentangled and described in terms of orbital occupancy, metal-ligand covalency, and ligand field splitting, thereby extending established steady-state concepts to the excited-state domain. pi-Back-donation is found to be mainly determined by the metal site occupation, whereas the ligand hole instead influences sigma-donation. Our results demonstrate how ultrafast resonant inelastic X-ray scattering can help characterize local charge distributions around catalytic metal centers in short-lived charge-transfer excited states, as a step toward future rationalization and tailoring of photocatalytic capabilities of transition-metal complexes.}, language = {en} } @article{NiskanenFondellSahleetal.2019, author = {Niskanen, Johannes and Fondell, Mattis and Sahle, Christoph J. and Eckert, Sebastian and Jay, Raphael Martin and Gilmore, Keith and Pietzsch, Annette and Dantz, Marcus and Lu, Xingye and McNally, Daniel E. and Schmitt, Thorsten and Vaz da Cruz, Vinicius and Kimberg, Victor and F{\"o}hlisch, Alexander and Gel'mukhanov, Faris}, title = {Compatibility of quantitative X-ray spectroscopy with continuous distribution models of water at ambient conditions}, series = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {116}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, number = {10}, publisher = {National Acad. of Sciences}, address = {Washington}, issn = {0027-8424}, doi = {10.1073/pnas.1815701116}, pages = {4058 -- 4063}, year = {2019}, abstract = {The phase diagram of water harbors controversial views on underlying structural properties of its constituting molecular moieties, its fluctuating hydrogen-bonding network, as well as pair-correlation functions. In this work, long energy-range detection of the X-ray absorption allows us to unambiguously calibrate the spectra for water gas, liquid, and ice by the experimental atomic ionization cross-section. In liquid water, we extract the mean value of 1.74 +/- 2.1\% donated and accepted hydrogen bonds per molecule, pointing to a continuous-distribution model. In addition, resonant inelastic X-ray scattering with unprecedented energy resolution also supports continuous distribution of molecular neighborhoods within liquid water, as do X-ray emission spectra once the femtosecond scattering duration and proton dynamics in resonant X-ray-matter interaction are taken into account. Thus, X-ray spectra of liquid water in ambient conditions can be understood without a two-structure model, whereas the occurrence of nanoscale-length correlations within the continuous distribution remains open.}, language = {en} } @article{VazdaCruzEckertIannuzzietal.2019, author = {Vaz da Cruz, Vinicius and Eckert, Sebastian and Iannuzzi, Marcella and Ertan, Emelie and Pietzsch, Annette and Couto, Rafael C. and Niskanen, Johannes and Fondell, Mattis and Dantz, Marcus and Schmitt, Thorsten and Lu, Xingye and McNally, Daniel and Jay, Raphael Martin and Kimberg, Victor and F{\"o}hlisch, Alexander and Odelius, Michael}, title = {Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering}, series = {Nature Communications}, volume = {10}, journal = {Nature Communications}, publisher = {Nature Publ. Group}, address = {London}, issn = {2041-1723}, doi = {10.1038/s41467-019-08979-4}, pages = {9}, year = {2019}, abstract = {Local probes of the electronic ground state are essential for understanding hydrogen bonding in aqueous environments. When tuned to the dissociative core-excited state at the O1s pre-edge of water, resonant inelastic X-ray scattering back to the electronic ground state exhibits a long vibrational progression due to ultrafast nuclear dynamics. We show how the coherent evolution of the OH bonds around the core-excited oxygen provides access to high vibrational levels in liquid water. The OH bonds stretch into the long-range part of the potential energy curve, which makes the X-ray probe more sensitive than infra-red spectroscopy to the local environment. We exploit this property to effectively probe hydrogen bond strength via the distribution of intramolecular OH potentials derived from measurements. In contrast, the dynamical splitting in the spectral feature of the lowest valence-excited state arises from the short-range part of the OH potential curve and is rather insensitive to hydrogen bonding.}, language = {en} } @article{JayEckertFondelletal.2018, author = {Jay, Raphael Martin and Eckert, Sebastian and Fondell, Mattis and Miedema, Piter S. and Norell, Jesper and Pietzsch, Annette and Quevedo, Wilson and Niskanen, Johannes and Kunnus, Kristjan and F{\"o}hlisch, Alexander}, title = {The nature of frontier orbitals under systematic ligand exchange in (pseudo-)octahedral Fe(II) complexes}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {20}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {44}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c8cp04341h}, pages = {27745 -- 27751}, year = {2018}, abstract = {Understanding and controlling properties of transition metal complexes is a crucial step towards tailoring materials for sustainable energy applications. In a systematic approach, we use resonant inelastic X-ray scattering to study the influence of ligand substitution on the valence electronic structure around an aqueous iron(II) center. Exchanging cyanide with 2-2′-bipyridine ligands reshapes frontier orbitals in a way that reduces metal 3d charge delocalization onto the ligands. This net decrease of metal-ligand covalency results in lower metal-centered excited state energies in agreement with previously reported excited state dynamics. Furthermore, traces of solvent-effects were found indicating a varying interaction strength of the solvent with ligands of different character. Our results demonstrate how ligand exchange can be exploited to shape frontier orbitals of transition metal complexes in solution-phase chemistry; insights upon which future efforts can built when tailoring the functionality of photoactive systems for light-harvesting applications.}, language = {en} } @article{EckertNorellJayetal.2019, author = {Eckert, Sebastian and Norell, Jesper and Jay, Raphael Martin and Fondell, Mattis and Mitzner, Rolf and Odelius, Michael and F{\"o}hlisch, Alexander}, title = {T-1 Population as the Driver of Excited-State Proton-Transfer in 2-Thiopyridone}, series = {Chemistry - a European journal}, volume = {25}, journal = {Chemistry - a European journal}, number = {7}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0947-6539}, doi = {10.1002/chem.201804166}, pages = {1733 -- 1739}, year = {2019}, abstract = {Excited-state proton transfer (ESPT) is a fundamental process in biomolecular photochemistry, but its underlying mediators often evade direct observation. We identify a distinct pathway for ESPT in aqueous 2-thiopyridone, by employing transient N1s X-ray absorption spectroscopy and multi-configurational spectrum simulations. Photoexcitations to the singlet S-2 and S-4 states both relax promptly through intersystem crossing to the triplet T-1 state. The T-1 state, through its rapid population and near nanosecond lifetime, mediates nitrogen site deprotonation by ESPT in a secondary intersystem crossing to the S-0 potential energy surface. This conclusively establishes a dominant ESPT pathway for the system in aqueous solution, which is also compatible with previous measurements in acetonitrile. Thereby, the hitherto open questions of the pathway for ESPT in the compound, including its possible dependence on excitation wavelength and choice of solvent, are resolved.}, language = {en} } @misc{NorellJayHantschmannetal.2018, author = {Norell, Jesper and Jay, Raphael and Hantschmann, Markus and Eckert, Sebastian and Guo, Meiyuan and Gaffney, Kelly and Wernet, Philippe and Lundberg, Marcus and F{\"o}hlisch, Alexander and Odelius, Michael}, title = {Fingerprints of electronic, spin and structural dynamics from resonant inelastic soft x-ray scattering in transient photo-chemical species}, series = {Physical chemistry, chemical physics}, journal = {Physical chemistry, chemical physics}, number = {20}, publisher = {RSC Publ.}, address = {Cambridge}, issn = {1463-9084}, doi = {10.1039/c7cp08326b}, pages = {7243 -- 7253}, year = {2018}, abstract = {We describe how inversion symmetry separation of electronic state manifolds in resonant inelastic soft X-ray scattering (RIXS) can be applied to probe excited-state dynamics with compelling selectivity. In a case study of Fe L3-edge RIXS in the ferricyanide complex Fe(CN)63-, we demonstrate with multi-configurational restricted active space spectrum simulations how the information content of RIXS spectral fingerprints can be used to unambiguously separate species of different electronic configurations, spin multiplicities, and structures, with possible involvement in the decay dynamics of photo-excited ligand-to-metal charge-transfer. Specifically, we propose that this could be applied to confirm or reject the presence of a hitherto elusive transient Quartet species. Thus, RIXS offers a particular possibility to settle a recent controversy regarding the decay pathway, and we expect the technique to be similarly applicable in other model systems of photo-induced dynamics.}, language = {en} } @article{JayEckertVazdaCruzetal.2019, author = {Jay, Raphael Martin and Eckert, Sebastian and Vaz da Cruz, Vinicius and Fondell, Mattis and Mitzner, Rolf and F{\"o}hlisch, Alexander}, title = {Covalency-driven preservation of local charge densities in a metal-to-ligand charge-transfer excited iron photosensitizer}, series = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, volume = {58}, journal = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, number = {31}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1433-7851}, doi = {10.1002/anie.201904761}, pages = {10742 -- 10746}, year = {2019}, abstract = {Charge-density rearrangements after metal-to-ligand charge-transfer excitation in an iron photosensitizer are investigated by R. M Jay, A. Fohlisch et al. in their Communication (DOI: 10.1002/anie.201904761). By using time-resolved X-ray absorption spectroscopy, surprising covalency-effects are revealed that inhibit charge-separation at the intra-molecular level. Furthermore, the underlying mechanism is proposed to be generally in effect for all commonly used photosensitizers in light-harvesting applications, which challenges the common perception of electronic charge-transfer.}, language = {en} } @article{EckertVazdaCruzErtanetal.2018, author = {Eckert, Sebastian and Vaz da Cruz, Vinicius and Ertan, Emelie and Ignatova, Nina and Polyutov, Sergey and Couto, Rafael C. and Fondell, Mattis and Dantz, Marcus and Kennedy, Brian and Schmitt, Thorsten and Pietzsch, Annette and Odelius, Michael and F{\"o}hlisch, Alexander}, title = {One-dimensional cuts through multidimensional potential-energy surfaces by tunable x rays}, series = {Physical review : A, Atomic, molecular, and optical physics}, volume = {97}, journal = {Physical review : A, Atomic, molecular, and optical physics}, number = {5}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9926}, doi = {10.1103/PhysRevA.97.053410}, pages = {7}, year = {2018}, abstract = {The concept of the potential-energy surface (PES) and directional reaction coordinates is the backbone of our description of chemical reaction mechanisms. Although the eigenenergies of the nuclear Hamiltonian uniquely link a PES to its spectrum, this information is in general experimentally inaccessible in large polyatomic systems. This is due to (near) degenerate rovibrational levels across the parameter space of all degrees of freedom, which effectively forms a pseudospectrum given by the centers of gravity of groups of close-lying vibrational levels. We show here that resonant inelastic x-ray scattering (RIXS) constitutes an ideal probe for revealing one-dimensional cuts through the ground-state PES of molecular systems, even far away from the equilibrium geometry, where the independent-mode picture is broken. We strictly link the center of gravity of close-lying vibrational peaks in RIXS to a pseudospectrum which is shown to coincide with the eigenvalues of an effective one-dimensional Hamiltonian along the propagation coordinate of the core-excited wave packet. This concept, combined with directional and site selectivity of the core-excited states, allows us to experimentally extract cuts through the ground-state PES along three complementary directions for the showcase H2O molecule.}, language = {en} } @article{PietzschNiskanenVazdaCruzetal.2022, author = {Pietzsch, Annette and Niskanen, Johannes and Vaz da Cruz, Vinicius and B{\"u}chner, Robby and Eckert, Sebastian and Fondell, Mattis and Jay, Raphael Martin and Lu, Xingye and McNally, Daniel and Schmitt, Thorsten and F{\"o}hlisch, Alexander}, title = {Cuts through the manifold of molecular H2O potential energy surfaces in liquid water at ambient conditions}, series = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {119}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, number = {28}, publisher = {National Acad. of Sciences}, address = {Washington, DC}, issn = {1091-6490}, doi = {10.1073/pnas.2118101119}, pages = {6}, year = {2022}, abstract = {The fluctuating hydrogen bridge bonded network of liquid water at ambient conditions entails a varied ensemble of the underlying constituting H2O molecular moieties. This is mirrored in a manifold of the H2O molecular potentials. Subnatural line width resonant inelastic X-ray scattering allowed us to quantify the manifold of molecular potential energy surfaces along the H2O symmetric normal mode and the local asymmetric O-H bond coordinate up to 1 and 1.5 angstrom, respectively. The comparison of the single H2O molecular potentials and spectroscopic signatures with the ambient conditions liquid phase H2O molecular potentials is done on various levels. In the gas phase, first principles, Morse potentials, and stepwise harmonic potential reconstruction have been employed and benchmarked. In the liquid phase the determination of the potential energy manifold along the local asymmetric O-H bond coordinate from resonant inelastic X-ray scattering via the bound state oxygen ls to 4a(1) resonance is treated within these frameworks. The potential energy surface manifold along the symmetric stretch from resonant inelastic X-ray scattering via the oxygen 1 s to 2b(2) resonance is based on stepwise harmonic reconstruction. We find in liquid water at ambient conditions H2O molecular potentials ranging from the weak interaction limit to strongly distorted potentials which are put into perspective to established parameters, i.e., intermolecular O-H, H-H, and O-O correlation lengths from neutron scattering.}, language = {en} } @article{ErtanSavchenkoIgnatovaetal.2018, author = {Ertan, Emelie and Savchenko, Viktoriia and Ignatova, Nina and Vaz da Cruz, Vinicius and Couto, Rafael C. and Eckert, Sebastian and Fondell, Mattis and Dantz, Marcus and Kennedy, Brian and Schmitt, Thorsten and Pietzsch, Annette and F{\"o}hlisch, Alexander and Odelius, Michael and Kimberg, Victor}, title = {Ultrafast dissociation features in RIXS spectra of the water molecule}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {20}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {21}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c8cp01807c}, pages = {14384 -- 14397}, year = {2018}, abstract = {In this combined theoretical and experimental study we report on an analysis of the resonant inelastic X-ray scattering (RIXS) spectra of gas phase water via the lowest dissociative core-excited state |1s-1O4a11〉. We focus on the spectral feature near the dissociation limit of the electronic ground state. We show that the narrow atomic-like peak consists of the overlapping contribution from the RIXS channels back to the ground state and to the first valence excited state |1b-114a11〉 of the molecule. The spectral feature has signatures of ultrafast dissociation (UFD) in the core-excited state, as we show by means of ab initio calculations and time-dependent nuclear wave packet simulations. We show that the electronically elastic RIXS channel gives substantial contribution to the atomic-like resonance due to the strong bond length dependence of the magnitude and orientation of the transition dipole moment. By studying the RIXS for an excitation energy scan over the core-excited state resonance, we can understand and single out the molecular and atomic-like contributions in the decay to the lowest valence-excited state. Our study is complemented by a theoretical discussion of RIXS in the case of isotopically substituted water (HDO and D2O) where the nuclear dynamics is significantly affected by the heavier fragments' mass.}, language = {en} } @article{JayVazdaCruzEckertetal.2020, author = {Jay, Raphael M. and Vaz da Cruz, Vinicius and Eckert, Sebastian and Fondell, Mattis and Mitzner, Rolf and F{\"o}hlisch, Alexander}, title = {Probing solute-solvent interactions of transition metal complexes using L-edge absorption spectroscopy}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {124}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, number = {27}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/acs.jpcb.0c00638}, pages = {5636 -- 5645}, year = {2020}, abstract = {In order to tailor solution-phase chemical reactions involving transition metal complexes, it is critical to understand how their valence electronic charge distributions are affected by the solution environment. Here, solute-solvent interactions of a solvatochromic mixed-ligand iron complex were investigated using X-ray absorption spectroscopy at the transition metal L-2,L-3-edge. Due to the selectivity of the corresponding core excitations to the iron 3d orbitals, the method grants direct access to the valence electronic structure around the iron center and its response to interactions with the solvent environment. A linear increase of the total L-2,L-3-edge absorption cross section as a function of the solvent Lewis acidity is revealed. The effect is caused by relative changes in different metal-ligand-bonding channels, which preserve local charge densities while increasing the density of unoccupied states around the iron center. These conclusions are corroborated by a combination of molecular dynamics and spectrum simulations based on time-dependent density functional theory. The simulations reproduce the spectral trends observed in the X-ray but also optical absorption experiments. Our results underscore the importance of solute-solvent interactions when aiming for an accurate description of the valence electronic structure of solvated transition metal complexes and demonstrate how L-2,L-3-edge absorption spectroscopy can aid in understanding the impact of the solution environment on intramolecular covalency and the electronic charge distribution.}, language = {en} } @article{VazdaCruzEckertFoehlisch2021, author = {Vaz da Cruz, Vin{\´i}cius and Eckert, Sebastian and F{\"o}hlisch, Alexander}, title = {TD-DFT simulations of K-edge resonant inelastic X-ray scattering within the restricted subspace approximation}, series = {Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies}, volume = {23}, journal = {Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies}, number = {3}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/d0cp04726k}, pages = {1835 -- 1848}, year = {2021}, abstract = {A scheme for simulations of resonant inelastic X-ray scattering (RIXS) cross-sections within time-dependent density functional theory (TD-DFT) applying the restricted subspace approximation (RSA) is presented. Therein both occupied core and valence Kohn-Sham orbitals are included in the donor-space, while the accepting virtual orbital space in the linear response TD-DFT equations is restricted to efficiently compute both the valence- and core-excited states of the many electron system. This yields a consistent description of all states contributing to the RIXS scattering process within a single calculation. The introduced orbital truncation allows to automatize the method and facilitates RIXS simulations for systems considerably larger than ones accessible with wave-function based methods. Using the nitrogen K-edge RIXS spectra of 2-thiopyridone and its deprotonated anion as a showcase, the method is benchmarked for different exchange-correlation functionals, the impact of the RSA is evaluated, and the effects of explicit solvation are discussed. Improvements compared to simulations in the frozen orbital approximation are also assessed. The general applicability of the framework is further tested by comparison to experimental data from the literature. The use of TD-DFT core-excited states to the calculation of vibrationally resolved RIXS spectra is also investigated by combining potential energy scans along relevant coordinates with wave packet simulations.}, language = {en} } @article{CoutoCruzErtanetal.2017, author = {Couto, Rafael C. and Cruz, Vinicius V. and Ertan, Emelie and Eckert, Sebastian and Fondell, Mattis and Dantz, Marcus and Kennedy, Brian and Schmitt, Thorsten and Pietzsch, Annette and Guimaraes, Freddy F. and Agren, Hans and Odelius, Michael and Kimberg, Victor and F{\"o}hlisch, Alexander}, title = {Selective gating to vibrational modes through resonant X-ray scattering}, series = {Nature Communications}, volume = {8}, journal = {Nature Communications}, publisher = {Nature Publ. Group}, address = {London}, issn = {2041-1723}, doi = {10.1038/ncomms14165}, pages = {7}, year = {2017}, abstract = {The dynamics of fragmentation and vibration of molecular systems with a large number of coupled degrees of freedom are key aspects for understanding chemical reactivity and properties. Here we present a resonant inelastic X-ray scattering (RIXS) study to show how it is possible to break down such a complex multidimensional problem into elementary components. Local multimode nuclear wave packets created by X-ray excitation to different core-excited potential energy surfaces (PESs) will act as spatial gates to selectively probe the particular ground-state vibrational modes and, hence, the PES along these modes. We demonstrate this principle by combining ultra-high resolution RIXS measurements for gas-phase water with state-of-the-art simulations.}, language = {en} } @article{JayEckertMitzneretal.2020, author = {Jay, Raphael M. and Eckert, Sebastian and Mitzner, Rolf and Fondell, Mattis and F{\"o}hlisch, Alexander}, title = {Quantitative evaluation of transient valence orbital occupations in a 3d transition metal complex as seen from the metal and ligand perspective}, series = {Chemical physics letters}, volume = {754}, journal = {Chemical physics letters}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0009-2614}, doi = {10.1016/j.cplett.2020.137681}, pages = {5}, year = {2020}, abstract = {It is demonstrated for the case of photo-excited ferrocyanide how time-resolved soft X-ray absorption spectroscopy in transmission geometry at the ligand K-edge and metal L-3-edge provides quantitatively equivalent valence electronic structure information, where signatures of photo-oxidation are assessed locally at the metal as well as the ligand. This allows for a direct and independent quantification of the number of photo-oxidized molecules at two soft X-ray absorption edges highlighting the sensitivity of X-ray absorption spectroscopy to the valence orbital occupation of 3d transition metal complexes throughout the soft X-ray range.}, language = {en} } @article{MascarenhasFondellBuechneretal.2022, author = {Mascarenhas, Eric Johnn and Fondell, Mattis and B{\"u}chner, Robby and Eckert, Sebastian and Vaz da Cruz, Vin{\´i}cius and F{\"o}hlisch, Alexander}, title = {Photo-induced ligand substitution of Cr(CO)(6) in 1-pentanol probed by time resolved X-ray absorption spectroscopy}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {24}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {30}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/d1cp05834g}, pages = {17979 -- 17985}, year = {2022}, abstract = {Cr(CO)(6) was investigated by X-ray absorption spectroscopy. The spectral signature at the metal edge provides information about the back-bonding of the metal in this class of complexes. Among the processes it participates in is ligand substitution in which a carbonyl ligand is ejected through excitation to a metal to ligand charge transfer (MLCT) band. The unsaturated carbonyl Cr(CO)(5) is stabilized by solution media in square pyramidal geometry and further reacts with the solvent. Multi-site-specific probing after photoexcitation was used to investigate the ligand substitution photoreaction process which is a common first step in catalytic processes involving metal carbonyls. The data were analysed with the aid of TD-DFT computations for different models of photoproducts and signatures for ligand rearrangement after substitution were found. The rearrangement was found to occur in about 790 ps in agreement with former studies of the photoreaction.}, language = {en} } @article{VazdaCruzBuechnerFondelletal.2022, author = {Vaz da Cruz, Vinicius and B{\"u}chner, Robby and Fondell, Mattis and Pietzsch, Annette and Eckert, Sebastian and F{\"o}hlisch, Alexander}, title = {Targeting individual tautomers in equilibrium by resonant inelastic X-ray scattering}, series = {The journal of physical chemistry letters}, volume = {13}, journal = {The journal of physical chemistry letters}, number = {10}, publisher = {American Chemical Society}, address = {Washington}, issn = {1948-7185}, doi = {10.1021/acs.jpclett.1c03453}, pages = {2459 -- 2466}, year = {2022}, abstract = {Tautomerism is one of the most important forms of isomerism, owing to the facile interconversion between species and the large differences in chemical properties introduced by the proton transfer connecting the tautomers. Spectroscopic techniques are often used for the characterization of tautomers. In this context, separating the overlapping spectral response of coexisting tautomers is a long-standing challenge in chemistry. Here, we demonstrate that by using resonant inelastic X-ray scattering tuned to the core excited states at the site of proton exchange between tautomers one is able to experimentally disentangle the manifold of valence excited states of each tautomer in a mixture. The technique is applied to the prototypical keto-enol equilibrium of 3-hydroxypyridine in aqueous solution. We detect transitions from the occupied orbitals into the LUMO for each tautomer in solution, which report on intrinsic and hydrogen-bond-induced orbital polarization within the pi and sigma manifolds at the proton-transfer site.}, language = {en} } @article{EckertBeyePietzschetal.2015, author = {Eckert, Sebastian and Beye, Martin and Pietzsch, Annette and Quevedo, Wilson and Hantschmann, Markus and Ochmann, Miguel and Ross, Matthew and Minitti, Michael P. and Turner, Joshua J. and Moeller, Stefan P. and Schlotter, William F. and Dakovski, Georgi L. and Khalil, Munira and Huse, Nils and F{\"o}hlisch, Alexander}, title = {Principles of femtosecond X-ray/optical cross-correlation with X-ray induced transient optical reflectivity in solids}, series = {Applied physics letters}, volume = {106}, journal = {Applied physics letters}, number = {6}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0003-6951}, doi = {10.1063/1.4907949}, pages = {4}, year = {2015}, abstract = {The discovery of ultrafast X-ray induced optical reflectivity changes enabled the development of X-ray/optical cross correlation techniques at X-ray free electron lasers worldwide. We have now linked through experiment and theory the fundamental excitation and relaxation steps with the transient optical properties in finite solid samples. Therefore, we gain a thorough interpretation and an optimized detection scheme of X-ray induced changes to the refractive index and the X-ray/optical cross correlation response. (C) 2015 AIP Publishing LLC.}, language = {en} } @article{EckertMascarenhasMitzneretal.2022, author = {Eckert, Sebastian and Mascarenhas, Eric Johnn and Mitzner, Rolf and Jay, Raphael Martin and Pietzsch, Annette and Fondell, Mattis and Vaz da Cruz, Vinicius and F{\"o}hlisch, Alexander}, title = {From the free ligand to the transition metal complex}, series = {Inorganic chemistry}, volume = {61}, journal = {Inorganic chemistry}, number = {27}, publisher = {American Chemical Society}, address = {Washington}, issn = {0020-1669}, doi = {10.1021/acs.inorgchem.2c00789}, pages = {10321 -- 10328}, year = {2022}, abstract = {Chelating agents are an integral part of transition metal complex chemistry with broad biological and industrial relevance. The hexadentate chelating agent ethylenediaminetetraacetic acid (EDTA) has the capability to bind to metal ions at its two nitrogen and four of its carboxylate oxygen sites. We use resonant inelastic X-ray scattering at the 1s absorption edge of the aforementioned elements in EDTA and the iron(III)-EDTA complex to investigate the impact of the metal-ligand bond formation on the electronic structure of EDTA. Frontier orbital distortions, occupation changes, and energy shifts through metal- ligand bond formation are probed through distinct spectroscopic signatures.}, language = {en} } @article{VazdaCruzIgnatovaCoutoetal.2019, author = {Vaz da Cruz, Vin{\´i}cius and Ignatova, Nina and Couto, Rafael and Fedotov, Daniil and Rehn, Dirk R. and Savchenko, Viktoriia and Norman, Patrick and {\AA}gren, Hans and Polyutov, Sergey and Niskanen, Johannes and Eckert, Sebastian and Jay, Raphael Martin and Fondell, Mattis and Schmitt, Thorsten and Pietzsch, Annette and F{\"o}hlisch, Alexander and Odelius, Michael and Kimberg, Victor and Gel'mukhanov, Faris}, title = {Nuclear dynamics in resonant inelastic X-ray scattering and X-ray absorption of methanol}, series = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, volume = {150}, journal = {The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr}, number = {23}, publisher = {American Institute of Physics}, address = {Melville}, issn = {0021-9606}, doi = {10.1063/1.5092174}, pages = {20}, year = {2019}, abstract = {We report on a combined theoretical and experimental study of core-excitation spectra of gas and liquid phase methanol as obtained with the use of X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS). The electronic transitions are studied with computational methods that include strict and extended second-order algebraic diagrammatic construction [ADC(2) and ADC(2)-x], restricted active space second-order perturbation theory, and time-dependent density functional theory-providing a complete assignment of the near oxygen K-edge XAS. We show that multimode nuclear dynamics is of crucial importance for explaining the available experimental XAS and RIXS spectra. The multimode nuclear motion was considered in a recently developed "mixed representation" where dissociative states and highly excited vibrational modes are accurately treated with a time-dependent wave packet technique, while the remaining active vibrational modes are described using Franck-Condon amplitudes. Particular attention is paid to the polarization dependence of RIXS and the effects of the isotopic substitution on the RIXS profile in the case of dissociative core-excited states. Our approach predicts the splitting of the 2a RIXS peak to be due to an interplay between molecular and pseudo-atomic features arising in the course of transitions between dissociative core- and valence-excited states. The dynamical nature of the splitting of the 2a peak in RIXS of liquid methanol near pre-edge core excitation is shown. The theoretical results are in good agreement with our liquid phase measurements and gas phase experimental data available from the literature. (C) 2019 Author(s).}, language = {en} } @article{SchreckBeyeSellbergetal.2014, author = {Schreck, Simon and Beye, Martin and Sellberg, Jonas A. and McQueen, Trevor and Laksmono, Hartawan and Kennedy, Brian and Eckert, Sebastian and Schlesinger, Daniel and Nordlund, Dennis and Ogasawara, Hirohito and Sierra, Raymond G. and Segtnan, Vegard H. and Kubicek, Katharina and Schlotter, William F. and Dakovski, Georgi L. and Moeller, Stefan P. and Bergmann, Uwe and Techert, Simone and Pettersson, Lars G. M. and Wernet, Philippe and Bogan, Michael J. and Harada, Yoshihisa and Nilsson, Anders and F{\"o}hlisch, Alexander}, title = {Reabsorption of soft x-ray emission at high x-ray free-electron laserfluences}, series = {Physical review letters}, volume = {113}, journal = {Physical review letters}, number = {15}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.113.153002}, pages = {6}, year = {2014}, abstract = {We report on oxygen K-edge soft x-ray emission spectroscopy from a liquid water jet at the Linac Coherent Light Source. We observe significant changes in the spectral content when tuning over a wide range of incident x-ray fluences. In addition the total emission yield decreases at high fluences. These modifications result from reabsorption of x-ray emission by valence-excited molecules generated by the Auger cascade. Our observations have major implications for future x-ray emission studies at intense x-ray sources. We highlight the importance of the x-ray pulse length with respect to the core-hole lifetime.}, language = {en} } @article{OchmannVazdaCruzEckertetal.2022, author = {Ochmann, Miguel and Vaz da Cruz, Vinicius and Eckert, Sebastian and Huse, Nils and F{\"o}hlisch, Alexander}, title = {R-Group stabilization in methylated formamides observed by resonant inelastic X-ray scattering}, series = {Chemical communications: ChemComm}, volume = {58}, journal = {Chemical communications: ChemComm}, number = {63}, publisher = {The Royal Society of Chemistry}, address = {Cambridge}, issn = {1359-7345}, doi = {10.1039/d2cc00053a}, pages = {8834 -- 8837}, year = {2022}, abstract = {The inherent stability of methylated formamides is traced to a stabilization of the deep-lying sigma-framework by resonant inelastic X-ray scattering at the nitrogen K-edge. Charge transfer from the amide nitrogen to the methyl groups underlie this stabilization mechanism that leaves the aldehyde group essentially unaltered and explains the stability of secondary and tertiary amides.}, language = {en} } @misc{NiskanenFondellSahleetal.2019, author = {Niskanen, Johannes and Fondell, Mattis and Sahle, Christoph J. and Eckert, Sebastian and Jay, Raphael Martin and Gilmore, Keith and Pietzsch, Annette and Dantz, Marcus and Lu, Xingye and McNally, Daniel E. and Schmitt, Thorsten and Vaz da Cruz, Vinicius and Kimberg, Victor and F{\"o}hlisch, Alexander}, title = {Reply to Pettersson et al.: Why X-ray spectral features are compatible to continuous distribution models in ambient water}, series = {Proceedings of the National Academy of Sciences of the United States of America}, volume = {116}, journal = {Proceedings of the National Academy of Sciences of the United States of America}, number = {35}, publisher = {National Acad. of Sciences}, address = {Washington}, issn = {0027-8424}, doi = {10.1073/pnas.1909551116}, pages = {17158 -- 17159}, year = {2019}, language = {en} } @misc{EckertMiedemaQuevedoetal.2016, author = {Eckert, Sebastian and Miedema, Piter and Quevedo, Wilson and O'Cinneide, B. and Fondell, Mattis and Beye, Martin and Pietzsch, Annette and Ross, Matthew R. and Khalil, Munira and F{\"o}hlisch, Alexander}, title = {Molecular structures and protonation state of 2-Mercaptopyridine in aqueous solution}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {953}, issn = {1866-8372}, doi = {10.25932/publishup-43747}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-437473}, pages = {103 -- 106}, year = {2016}, abstract = {The speciation of 2-Mercaptopyridine in aqueous solution has been investigated with nitrogen 1s Near Edge X-ray Absorption Fine Structure spectroscopy and time dependent Density Functional Theory. The prevalence of distinct species as a function of the solvent basicity is established. No indications of dimerization towards high concentrations are found. The determination of different molecular structures of 2-Mercaptopyridine in aqueous solution is put into the context of proton-transfer in keto-enol and thione-thiol tautomerisms. (C) 2016 The Authors. Published by Elsevier B.V.}, language = {en} } @article{SorgenfreiGiangrisostomiJayetal.2021, author = {Sorgenfrei, Nomi and Giangrisostomi, Erika and Jay, Raphael Martin and K{\"u}hn, Danilo and Neppl, Stefan and Ovsyannikov, Ruslan and Sezen, Hikmet and Svensson, Svante and F{\"o}hlisch, Alexander}, title = {Photodriven transient picosecond top-layer semiconductor to metal phase-transition in p-doped molybdenum disulfide}, series = {Advanced materials}, volume = {33}, journal = {Advanced materials}, number = {14}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0935-9648}, doi = {10.1002/adma.202006957}, pages = {8}, year = {2021}, abstract = {Visible light is shown to create a transient metallic S-Mo-S surface layer on bulk semiconducting p-doped indirect-bandgap 2H-MoS2. Optically created electron-hole pairs separate in the surface band bending region of the p-doped semiconducting crystal causing a transient accumulation of electrons in the surface region. This triggers a reversible 2H-semiconductor to 1T-metal phase-transition of the surface layer. Electron-phonon coupling of the indirect-bandgap p-doped 2H-MoS2 enables this efficient pathway even at a low density of excited electrons with a distinct optical excitation threshold and saturation behavior. This mechanism needs to be taken into consideration when describing the surface properties of illuminated p-doped 2H-MoS2. In particular, light-induced increased charge mobility and surface activation can cause and enhance the photocatalytic and photoassisted electrochemical hydrogen evolution reaction of water on 2H-MoS2. Generally, it opens up for a way to control not only the surface of p-doped 2H-MoS2 but also related dichalcogenides and layered systems. The findings are based on the sensitivity of time-resolved electron spectroscopy for chemical analysis with photon-energy-tuneable synchrotron radiation.}, language = {en} } @article{CappelSvanstromLanzilottoetal.2017, author = {Cappel, Ute B. and Svanstrom, Sebastian and Lanzilotto, Valeria and Johansson, Fredrik O. L. and Aitola, Kerttu and Philippe, Bertrand and Giangrisostomi, Erika and Ovsyannikov, Ruslan and Leitner, Torsten and F{\"o}hlisch, Alexander and Svensson, Svante and Martensson, Nils and Boschloo, Gerrit and Lindblad, Andreas and Rensmo, Hakan}, title = {Partially Reversible Photoinduced Chemical Changes in a Mixed-Ion Perovskite Material for Solar Cells}, series = {ACS applied materials \& interfaces}, volume = {9}, journal = {ACS applied materials \& interfaces}, publisher = {American Chemical Society}, address = {Washington}, issn = {1944-8244}, doi = {10.1021/acsami.7b10643}, pages = {34970 -- 34978}, year = {2017}, abstract = {Metal halide perovskites have emerged as materials of high interest for solar energy-to-electricity conversion, and in particular, the use of mixed-ion structures has led to high power conversion efficiencies and improved stability. For this reason, it is important to develop means to obtain atomic level understanding of the photoinduced behavior of these materials including processes such as photoinduced phase separation and ion migration. In this paper, we implement a new methodology combining visible laser illumination of a mixed-ion perovskite ((FAP-bI(3))(0.85)(MAPbBr(3))(0.15)) with the element specificity and chemical sensitivity of core-level photoelectron spectroscopy. By carrying out measurements at a synchrotron beamline optimized for low X-ray fluxes, we are able to avoid sample changes due to X-ray illumination and are therefore able to monitor what sample changes are induced by visible illumination only. We find that laser illumination causes partially reversible chemistry in the surface region, including enrichment of bromide at the surface, which could be related to a phase separation into bromide- and iodide-rich phases. We also observe a partially reversible formation of metallic lead in the perovskite structure. These processes occur on the time scale of minutes during illumination. The presented methodology has a large potential for understanding light-induced chemistry in photoactive materials and could specifically be extended to systematically study the impact of morphology and composition on the photostability of metal halide perovskites.}, language = {en} } @misc{EckertNorellMiedemaetal.2017, author = {Eckert, Sebastian and Norell, Jesper and Miedema, Piter S. and Beye, Martin and Fondell, Mattis and Quevedo, Wilson and Kennedy, Brian and Hantschmann, Markus and Pietzsch, Annette and van Kuiken, Benjamin E. and Ross, Matthew and Minitti, Michael P. and Moeller, Stefan P. and Schlotter, William F. and Khalil, Munira and Odelius, Michael and F{\"o}hlisch, Alexander}, title = {Untersuchung unabh{\"a}ngiger N-H- und N-C-Bindungsverformungen auf ultrakurzen Zeitskalen mit resonanter inelastischer R{\"o}ntgenstreuung}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1121}, issn = {1866-8372}, doi = {10.25932/publishup-43668}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436688}, pages = {7}, year = {2017}, abstract = {Die Femtosekundendynamik nach resonanten Photoanregungen mit optischen und R{\"o}ntgenpulsen erm{\"o}glicht eine selektive Verformung von chemischen N-H- und N-C-Bindungen in 2-Thiopyridon in w{\"a}ssriger L{\"o}sung. Die Untersuchung der orbitalspezifischen elektronischen Struktur und ihrer Dynamik auf ultrakurzen Zeitskalen mit resonanter inelastischer R{\"o}ntgenstreuung an der N1s-Resonanz am Synchrotron und dem Freie-Elektronen-Laser LCLS in Kombination mit quantenchemischen Multikonfigurationsberechnungen erbringen den direkten Nachweis dieser kontrollierten photoinduzierten Molek{\"u}lverformungen und ihrer ultrakurzen Zeitskala.}, language = {de} } @misc{CoutoCruzErtanetal.2017, author = {Couto, Rafael C. and Cruz, Vinicius V. and Ertan, Emelie and Eckert, Sebastian and Fondell, Mattis and Dantz, Marcus and Kennedy, Brian and Schmitt, Thorsten and Pietzsch, Annette and Guimar{\~a}es, Freddy F. and {\AA}gren, Hans and Gel'mukhanov, Faris and Odelius, Michael and Kimberg, Victor and F{\"o}hlisch, Alexander}, title = {Selective gating to vibrational modes through resonant X-ray scattering}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1124}, issn = {1866-8372}, doi = {10.25932/publishup-43692}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436926}, pages = {9}, year = {2017}, abstract = {The dynamics of fragmentation and vibration of molecular systems with a large number of coupled degrees of freedom are key aspects for understanding chemical reactivity and properties. Here we present a resonant inelastic X-ray scattering (RIXS) study to show how it is possible to break down such a complex multidimensional problem into elementary components. Local multimode nuclear wave packets created by X-ray excitation to different core-excited potential energy surfaces (PESs) will act as spatial gates to selectively probe the particular ground-state vibrational modes and, hence, the PES along these modes. We demonstrate this principle by combining ultra-high resolution RIXS measurements for gas-phase water with state-of-the-art simulations.}, language = {en} } @misc{EckertNorellMiedemaetal.2017, author = {Eckert, Sebastian and Norell, Jesper and Miedema, Piter S. and Beye, Martin and Fondell, Mattis and Quevedo, Wilson and Kennedy, Brian and Hantschmann, Markus and Pietzsch, Annette and van Kuiken, Benjamin E. and Ross, Matthew and Minitti, Michael P. and Moeller, Stefan P. and Schlotter, William F. and Khalil, Munira and Odelius, Michael and F{\"o}hlisch, Alexander}, title = {Ultrafast Independent N-H and N-C Bond Deformation Investigated with Resonant Inelastic X-Ray Scattering}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {1115}, issn = {1866-8372}, doi = {10.25932/publishup-43687}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436873}, pages = {7}, year = {2017}, abstract = {The femtosecond excited-state dynamics following resonant photoexcitation enable the selective deformation of N-H and N-C chemical bonds in 2-thiopyridone in aqueous solution with optical or X-ray pulses. In combination with multiconfigurational quantum-chemical calculations, the orbital-specific electronic structure and its ultrafast dynamics accessed with resonant inelastic X-ray scattering at the N 1s level using synchrotron radiation and the soft X-ray free-electron laser LCLS provide direct evidence for this controlled photoinduced molecular deformation and its ultrashort time-scale.}, language = {en} } @misc{VazdaCruzErtanCoutoetal.2017, author = {Vaz da Cruz, Vinicius and Ertan, Emelie and Couto, Rafael C. and Eckert, Sebastian and Fondell, Mattis and Dantz, Marcus and Kennedy, Brian and Schmitt, Thorsten and Pietzsch, Annette and Guimar{\~a}es, Freddy F. and {\AA}gren, Hans and Gel'mukhanov, Faris and Odelius, Michael and F{\"o}hlisch, Alexander and Kimberg, Victor}, title = {A study of the water molecule using frequency control over nuclear dynamics in resonant X-ray scattering}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {781}, issn = {1866-8372}, doi = {10.25932/publishup-43690}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-436901}, pages = {19573 -- 19589}, year = {2017}, abstract = {In this combined theoretical and experimental study we report a full analysis of the resonant inelastic X-ray scattering (RIXS) spectra of H2O, D2O and HDO. We demonstrate that electronically-elastic RIXS has an inherent capability to map the potential energy surface and to perform vibrational analysis of the electronic ground state in multimode systems. We show that the control and selection of vibrational excitation can be performed by tuning the X-ray frequency across core-excited molecular bands and that this is clearly reflected in the RIXS spectra. Using high level ab initio electronic structure and quantum nuclear wave packet calculations together with high resolution RIXS measurements, we discuss in detail the mode coupling, mode localization and anharmonicity in the studied systems.}, language = {en} } @misc{NorellJayHantschmannetal.2018, author = {Norell, Jesper and Jay, Raphael Martin and Hantschmann, Markus and Eckert, Sebastian and Guo, Meiyuan and Gaffney, Kelly J. and Wernet, Philippe and Lundberg, Marcus and F{\"o}hlisch, Alexander and Odelius, Michael}, title = {Fingerprints of electronic, spin and structural dynamics from resonant inelastic soft X-ray scattering in transient photo-chemical species}, series = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam Mathematisch-Naturwissenschaftliche Reihe}, number = {779}, issn = {1866-8372}, doi = {10.25932/publishup-43749}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-437493}, pages = {7243 -- 7253}, year = {2018}, abstract = {We describe how inversion symmetry separation of electronic state manifolds in resonant inelastic soft X-ray scattering (RIXS) can be applied to probe excited-state dynamics with compelling selectivity. In a case study of Fe L-3-edge RIXS in the ferricyanide complex Fe(CN)(6)(3-), we demonstrate with multi-configurational restricted active space spectrum simulations how the information content of RIXS spectral fingerprints can be used to unambiguously separate species of different electronic configurations, spin multiplicities, and structures, with possible involvement in the decay dynamics of photo-excited ligand-to-metal charge-transfer. Specifically, we propose that this could be applied to confirm or reject the presence of a hitherto elusive transient Quartet species. Thus, RIXS offers a particular possibility to settle a recent controversy regarding the decay pathway, and we expect the technique to be similarly applicable in other model systems of photo-induced dynamics.}, language = {en} }