TY - JOUR A1 - Kühn, Danilo A1 - Müller, Moritz A1 - Sorgenfrei, Florian A1 - Giangrisostomi, Erika A1 - Jay, Raphael Martin A1 - Ovsyannikov, Ruslan A1 - Martensson, Nils A1 - Sanchez-Portal, Daniel A1 - Föhlisch, Alexander T1 - Directional sub-femtosecond charge transfer dynamics and the dimensionality of 1T-TaS2 JF - Scientific reports N2 - For the layered transition metal dichalcogenide 1T-TaS2, we establish through a unique experimental approach and density functional theory, how ultrafast charge transfer in 1T-TaS2 takes on isotropic three-dimensional character or anisotropic two-dimensional character, depending on the commensurability of the charge density wave phases of 1T-TaS2. The X-ray spectroscopic core-hole-clock method prepares selectively in-and out-of-plane polarized sulfur 3p orbital occupation with respect to the 1T-TaS2 planes and monitors sub-femtosecond wave packet delocalization. Despite being a prototypical two-dimensional material, isotropic three-dimensional charge transfer is found in the commensurate charge density wave phase (CCDW), indicating strong coupling between layers. In contrast, anisotropic two-dimensional charge transfer occurs for the nearly commensurate phase (NCDW). In direct comparison, theory shows that interlayer interaction in the CCDW phase - not layer stacking variations - causes isotropic three-dimensional charge transfer. This is presumably a general mechanism for phase transitions and tailored properties of dichalcogenides with charge density waves. Y1 - 2019 U6 - https://doi.org/10.1038/s41598-018-36637-0 SN - 2045-2322 VL - 9 IS - 488 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Kühn, Danilo A1 - Sorgenfrei, Florian A1 - Giangrisostomi, Erika A1 - Jay, Raphael A1 - Musazay, Abdurrahman A1 - Ovsyannikov, Ruslan A1 - Strahlman, Christian A1 - Svensson, Svante A1 - Mårtensson, Nils A1 - Föhlisch, Alexander T1 - Capabilities of angle resolved time of flight electron spectroscopy with the 60 degrees wide angle acceptance lens JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - The simultaneous detection of energy, momentum and temporal information in electron spectroscopy is the key aspect to enhance the detection efficiency in order to broaden the range of scientific applications. Employing a novel 60 degrees wide angle acceptance lens system, based on an additional accelerating electron optical element, leads to a significant enhancement in transmission over the previously employed 30 degrees electron lenses. Due to the performance gain, optimized capabilities for time resolved electron spectroscopy and other high transmission applications with pulsed ionizing radiation have been obtained. The energy resolution and transmission have been determined experimentally utilizing BESSY II as a photon source. Four different and complementary lens modes have been characterized. (C) 2017 The Authors. Published by Elsevier B.V. KW - Artof KW - Electron spectroscopy KW - Wide angle KW - Time of flight KW - Energy resolution KW - Synchrotron Y1 - 2018 U6 - https://doi.org/10.1016/j.elspec.2017.06.008 SN - 0368-2048 SN - 1873-2526 VL - 224 SP - 45 EP - 50 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kunnus, Kristjan A1 - Josefsson, I. A1 - Schreck, Simon Frederik A1 - Quevedo, W. A1 - Miedema, P. S. A1 - Techert, S. A1 - de Groot, F. M. F. A1 - Föhlisch, Alexander A1 - Odelius, M. A1 - Wernet, Ph. T1 - Quantifying covalent interactions with resonant inelastic soft X-ray scattering BT - case study of Ni2+ aqua complex JF - Chemical physics letters N2 - 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. KW - Transition-metal ion KW - Aqueous solution KW - Covalent interaction KW - Resonant inelastic X-ray scattering KW - Ligand-field state KW - Charge-transfer state Y1 - 2016 U6 - https://doi.org/10.1016/j.cplett.2016.12.046 SN - 0009-2614 SN - 1873-4448 VL - 669 SP - 196 EP - 201 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Leitner, T. A1 - Josefsson, Ida A1 - Mazza, T. A1 - Miedema, Piter S. A1 - Schröder, H. A1 - Beye, Martin A1 - Kunnus, Kristjan A1 - Schreck, S. A1 - Düsterer, Stefan A1 - Föhlisch, Alexander A1 - Meyer, M. A1 - Odelius, Michael A1 - Wernet, Philippe T1 - Time-resolved electron spectroscopy for chemical analysis of photodissociation BT - Photoelectron spectra of Fe(CO)(5), Fe(CO)(4), and Fe(CO)(3) JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - 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. Y1 - 2018 U6 - https://doi.org/10.1063/1.5035149 SN - 0021-9606 SN - 1089-7690 VL - 149 IS - 4 PB - American Institute of Physics CY - Melville ER - TY - GEN A1 - Jay, Raphael J. A1 - Norell, Jesper A1 - Kunnus, Kristjan A1 - Lundberg, Marcus A1 - Gaffney, Kelly A1 - Wernet, Philippe A1 - Odelius, Michael A1 - Föhlisch, Alexander T1 - Dynamcis of local charge densities and metal-ligand covalency in iron complexes from femtosecond resonant inelastic soft X-ray scattering T2 - Abstracts of Papers of the American Chemical Society Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:se:uu:diva-370051 SN - 0065-7727 VL - 256 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Kühn, Danilo A1 - Giangrisostomi, Erika A1 - Jay, Raphael Martin A1 - Sorgenfrei, Florian A1 - Föhlisch, Alexander T1 - The influence of x-ray pulse length on space-charge effects in optical pump/x-ray probe photoemission JF - New journal of physics : the open-access journal for physics N2 - Pump-probe photoelectron spectroscopy (PES) is a versatile tool to investigate the dynamics of transient states of excited matter. Vacuum space-charge effects can mask these dynamics and complicate the interpretation of electron spectra. Here we report on space-charge effects in Au 4f photoemission from a polycrystalline gold surface, excited with moderately intense 90 ps (FWHM) soft x-ray probe pulses, under the influence of the Coulomb forces exerted by a pump electron cloud, which was produced by intense 40 fs laser pulses. The experimentally observed kinetic energy shift and spectral broadening of the Au 4f lines, measured with highly-efficient time-of-flight spectroscopy, are in good agreement with simulations utilizing a mean-field model of the electrostatic pump electron potential. This confirms that the line broadening is predominantly caused by variations in the take-off time of the probe electrons without appreciable influence of local scattering events. Our findings might be of general interest for pump-probe PES with picosecond-pulse-length sources. KW - space-charge effects KW - mean-field model KW - x-ray photoemission KW - electron spectroscopy KW - pump-probe KW - ARTOF Y1 - 2019 U6 - https://doi.org/10.1088/1367-2630/ab2f5c SN - 1367-2630 VL - 21 PB - IOP Publ. Ltd. CY - Bristol ER - TY - GEN A1 - Kühn, Danilo A1 - Sorgenfrei, Florian A1 - Giangrisostomi, Erika A1 - Jay, Raphael Martin A1 - Musazayb, Abdurrahman A1 - Ovsyannikov, Ruslan A1 - Stråhlman, Christian A1 - Svensson, Svante A1 - Mårtensson, Nils A1 - Föhlisch, Alexander T1 - Capabilities of angle resolved time of flight electron spectroscopy with the 60 degrees wide angle acceptance lens T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - The simultaneous detection of energy, momentum and temporal information in electron spectroscopy is the key aspect to enhance the detection efficiency in order to broaden the range of scientific applications. Employing a novel 60 degrees wide angle acceptance lens system, based on an additional accelerating electron optical element, leads to a significant enhancement in transmission over the previously employed 30 degrees electron lenses. Due to the performance gain, optimized capabilities for time resolved electron spectroscopy and other high transmission applications with pulsed ionizing radiation have been obtained. The energy resolution and transmission have been determined experimentally utilizing BESSY II as a photon source. Four different and complementary lens modes have been characterized. (C) 2017 The Authors. Published by Elsevier B.V. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 782 KW - Artof KW - electron spectroscopy KW - wide angle KW - time of flight KW - energy resolution KW - synchrotron Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-436629 SN - 1866-8372 IS - 782 SP - 45 EP - 50 ER - TY - JOUR A1 - Ovsyannikov, Ruslan A1 - Karlsson, P. A1 - Lundqvist, M. A1 - Lupulescu, C. A1 - Eberhardt, W. A1 - Föhlisch, Alexander A1 - Svensson, S. A1 - Martensson, N. T1 - Principles and operation of a new type of electron spectrometer - ArTOF JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - 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. KW - ARPES KW - Time of flight KW - Synchrotron KW - Electron spectroscopy Y1 - 2013 U6 - https://doi.org/10.1016/j.elspec.2013.08.005 SN - 0368-2048 SN - 1873-2526 VL - 191 IS - 12 SP - 92 EP - 103 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kunnus, Kristjan A1 - Josefsson, Ida A1 - Schreck, Simon A1 - Quevedo, Wilson A1 - Miedema, Piter S. A1 - Techert, Simone A1 - de Groot, Frank M. F. A1 - Odelius, Michael A1 - Wernet, Philippe A1 - Föhlisch, Alexander T1 - From Ligand Fields to Molecular Orbitals: Probing the Local Valence Electronic Structure of Ni2+ in Aqueous Solution with Resonant Inelastic X-ray Scattering JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - 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. Y1 - 2013 U6 - https://doi.org/10.1021/jp4100813 SN - 1520-6106 VL - 117 IS - 51 SP - 16512 EP - 16521 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Dell'Angela, M. A1 - Anniyev, Toyli A1 - Beye, Martin A1 - Coffee, Ryan A1 - Föhlisch, Alexander A1 - Gladh, J. A1 - Katayama, T. A1 - Kaya, S. A1 - Krupin, O. A1 - LaRue, J. A1 - Mogelhoj, A. A1 - Nordlund, D. A1 - Norskov, J. K. A1 - Oberg, H. A1 - Ogasawara, H. A1 - Ostrom, H. A1 - Pettersson, Lars G. M. A1 - Schlotter, W. F. A1 - Sellberg, J. A. A1 - Sorgenfrei, Florian A1 - Turner, J. J. A1 - Wolf, M. A1 - Wurth, W. A1 - Nilsson, A. T1 - Real-time observation of surface bond breaking with an X-ray Laser JF - Science N2 - We used the Linac Coherent Light Source free-electron x-ray laser to probe the electronic structure of CO molecules as their chemisorption state on Ru(0001) changes upon exciting the substrate by using a femtosecond optical laser pulse. We observed electronic structure changes that are consistent with a weakening of the CO interaction with the substrate but without notable desorption. A large fraction of the molecules (30%) was trapped in a transient precursor state that would precede desorption. We calculated the free energy of the molecule as a function of the desorption reaction coordinate using density functional theory, including van der Waals interactions. Two distinct adsorption wells-chemisorbed and precursor state separated by an entropy barrier-explain the anomalously high prefactors often observed in desorption of molecules from metals. Y1 - 2013 U6 - https://doi.org/10.1126/science.1231711 SN - 0036-8075 VL - 339 IS - 6125 SP - 1302 EP - 1305 PB - American Assoc. for the Advancement of Science CY - Washington ER - TY - JOUR A1 - Beye, Martin A1 - Föhlisch, Alexander T1 - Soft X-ray probes of ultrafast dynamics for heterogeneous catalysis JF - Chemical physics : a journal devoted to experimental and theoretical research involving problems of both a chemical and physical nature N2 - 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. KW - Core-hole clock KW - Resonant inelastic X-ray scattering KW - Ultrafast surface science KW - Photoelectron spectroscopy Y1 - 2013 U6 - https://doi.org/10.1016/j.chemphys.2012.03.023 SN - 0301-0104 SN - 1873-4421 VL - 414 IS - 5 SP - 130 EP - 138 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Katayama, T. A1 - Anniyev, Toyli A1 - Beye, Martin A1 - Coffee, Ryan A1 - Dell'Angela, M. A1 - Föhlisch, Alexander A1 - Gladh, J. A1 - Kaya, S. A1 - Krupin, O. A1 - Nilsson, A. A1 - Nordlund, D. A1 - Schlotter, W. F. A1 - Sellberg, J. A. A1 - Sorgenfrei, Florian A1 - Turner, J. J. A1 - Wurth, W. A1 - Öström, H. A1 - Ogasawara, H. T1 - Ultrafast soft X-ray emission spectroscopy of surface adsorbates using an X-ray free electron laser JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - We report on an experimental system designed to probe chemical reactions on solid surfaces on a sub-picosecond timescale using soft X-ray emission spectroscopy at the Linac Coherent Light Source (LCLS) free electron laser (FEL) at the SLAC National Accelerator Laboratory. We analyzed the O 1s X-ray emission spectra recorded from atomic oxygen adsorbed on a Ru(0001) surface at a synchrotron beamline (SSRL, BL13-2) and an FEL beamline (LCLS, SXR). We have demonstrated conditions that provide negligible amount of FEL induced damage of the sample. In addition we show that the setup is capable of tracking the temporal evolution of electronic structure during a surface reaction of submonolayer quantities of CO molecules desorbing from the surface. KW - X-ray emission spectroscopy KW - Surface science KW - Free electron laser KW - Ultrafast Y1 - 2013 U6 - https://doi.org/10.1016/j.elspec.2013.03.006 SN - 0368-2048 VL - 187 IS - 1 SP - 9 EP - 14 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Könnecke, Rene A1 - Follath, R. A1 - Pontius, N. A1 - Schlappa, J. A1 - Eggenstein, F. A1 - Zeschke, T. A1 - Bischoff, P. A1 - Schmidt, J. -S. A1 - Noll, T. A1 - Trabant, C. A1 - Schreck, S. A1 - Wernet, Ph. A1 - Eisebitt, S. A1 - Senf, F. A1 - Schuessler-Langeheine, Christian A1 - Erko, A. A1 - Föhlisch, Alexander T1 - The confocal plane grating spectrometer at BESSY II JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - 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. KW - Resonant inelastic X-ray scattering KW - Soft X-ray monochromator KW - High transmission micro focus beamline KW - Plane grating emission spectrometer Y1 - 2013 U6 - https://doi.org/10.1016/j.elspec.2012.11.003 SN - 0368-2048 VL - 188 SP - 133 EP - 139 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Beye, Martin A1 - Wernet, Ph. A1 - Schüßler-Langeheine, Christian A1 - Föhlisch, Alexander T1 - Time resolved resonant inelastic X-ray scattering: a supreme tool to understand dynamics in solids and molecules JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - 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. KW - Resonant inelastic X-ray scattering KW - Ultrafast spectroscopy KW - Phase transitions KW - Molecular dynamics Y1 - 2013 U6 - https://doi.org/10.1016/j.elspec.2013.04.013 SN - 0368-2048 VL - 188 IS - 3 SP - 172 EP - 182 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Beye, Martin A1 - Schreck, S. A1 - Sorgenfrei, Florian A1 - Trabant, C. A1 - Pontius, N. A1 - Schüßler-Langeheine, C. A1 - Wurth, W. A1 - Föhlisch, Alexander T1 - Stimulated X-ray emission for materials science JF - Nature : the international weekly journal of science N2 - Resonant inelastic X-ray scattering and X-ray emission spectroscopy can be used to probe the energy and dispersion of the elementary low-energy excitations that govern functionality in matter: vibronic, charge, spin and orbital excitations(1-7). A key drawback of resonant inelastic X-ray scattering has been the need for high photon densities to compensate for fluorescence yields of less than a per cent for soft X-rays(8). Sample damage from the dominant non-radiative decays thus limits the materials to which such techniques can be applied and the spectral resolution that can be obtained. A means of improving the yield is therefore highly desirable. Here we demonstrate stimulated X-ray emission for crystalline silicon at photon densities that are easily achievable with free-electron lasers(9). The stimulated radiative decay of core excited species at the expense of non-radiative processes reduces sample damage and permits narrow-bandwidth detection in the directed beam of stimulated radiation. We deduce how stimulated X-ray emission can be enhanced by several orders of magnitude to provide, with high yield and reduced sample damage, a superior probe for low-energy excitations and their dispersion in matter. This is the first step to bringing nonlinear X-ray physics in the condensed phase from theory(10-16) to application. Y1 - 2013 U6 - https://doi.org/10.1038/nature12449 SN - 0028-0836 VL - 501 IS - 7466 SP - 191 EP - + PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - de Jong, S. A1 - Kukreja, R. A1 - Trabant, C. A1 - Pontius, N. A1 - Chang, C. F. A1 - Kachel, T. A1 - Beye, Martin A1 - Sorgenfrei, Florian A1 - Back, C. H. A1 - Braeuer, B. A1 - Schlotter, W. F. A1 - Turner, J. J. A1 - Krupin, O. A1 - Doehler, M. A1 - Zhu, D. A1 - Hossain, M. A. A1 - Scherz, A. O. A1 - Fausti, D. A1 - Novelli, F. A1 - Esposito, M. A1 - Lee, W. S. A1 - Chuang, Y. D. A1 - Lu, D. H. A1 - Moore, R. G. A1 - Yi, M. A1 - Trigo, M. A1 - Kirchmann, P. A1 - Pathey, L. A1 - Golden, M. S. A1 - Buchholz, Marcel A1 - Metcalf, P. A1 - Parmigiani, F. A1 - Wurth, W. A1 - Föhlisch, Alexander A1 - Schuessler-Langeheine, Christian A1 - Duerr, H. A. T1 - Speed limit of the insulator-metal transition in magnetite JF - Nature materials N2 - As the oldest known magnetic material, magnetite (Fe3O4) has fascinated mankind for millennia. As the first oxide in which a relationship between electrical conductivity and fluctuating/localized electronic order was shown(1), magnetite represents a model system for understanding correlated oxides in general. Nevertheless, the exact mechanism of the insulator-metal, or Verwey, transition has long remained inaccessible(2-8). Recently, three- Fe- site lattice distortions called trimeronswere identified as the characteristic building blocks of the low-temperature insulating electronically ordered phase(9). Here we investigate the Verwey transition with pump- probe X- ray diffraction and optical reflectivity techniques, and show how trimerons become mobile across the insulator-metal transition. We find this to be a two- step process. After an initial 300 fs destruction of individual trimerons, phase separation occurs on a 1.5 +/- 0.2 ps timescale to yield residual insulating and metallic regions. This work establishes the speed limit for switching in future oxide electronics(10). Y1 - 2013 U6 - https://doi.org/10.1038/NMAT3718 SN - 1476-1122 SN - 1476-4660 VL - 12 IS - 10 SP - 882 EP - 886 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Beye, Martin A1 - Anniyev, Toyli A1 - Coffee, Ryan A1 - Dell'Angela, Martina A1 - Föhlisch, Alexander A1 - Gladh, J. A1 - Katayama, T. A1 - Kaya, S. A1 - Krupin, O. A1 - Mogelhoj, A. A1 - Nilsson, A. A1 - Nordlund, D. A1 - Norskov, J. K. A1 - Oberg, H. A1 - Ogasawara, H. A1 - Pettersson, Lars G. M. A1 - Schlotter, W. F. A1 - Sellberg, J. A. A1 - Sorgenfrei, Florian A1 - Turner, J. J. A1 - Wolf, M. A1 - Wurth, Wilfried A1 - Ostrom, H. T1 - Selective ultrafast probing of transient hot chemisorbed and precursor States of CO on Ru(0001) JF - Physical review letters N2 - We have studied the femtosecond dynamics following optical laser excitation of CO adsorbed on a Ru surface by monitoring changes in the occupied and unoccupied electronic structure using ultrafast soft x-ray absorption and emission. We recently reported [M. Dell'Angela et al. Science 339, 1302 (2013)] a phonon-mediated transition into a weakly adsorbed precursor state occurring on a time scale of >2 ps prior to desorption. Here we focus on processes within the first picosecond after laser excitation and show that the metal-adsorbate coordination is initially increased due to hot-electron-driven vibrational excitations. This process is faster than, but occurs in parallel with, the transition into the precursor state. With resonant x-ray emission spectroscopy, we probe each of these states selectively and determine the respective transient populations depending on optical laser fluence. Ab initio molecular dynamics simulations of CO adsorbed on Ru(0001) were performed at 1500 and 3000 K providing insight into the desorption process. Y1 - 2013 U6 - https://doi.org/10.1103/PhysRevLett.110.186101 SN - 0031-9007 VL - 110 IS - 18 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Pontius, N. A1 - Kachel, T. A1 - Schüssler-Langeheine, C. A1 - Schlotter, W. F. A1 - Beye, Martin A1 - Sorgenfrei, Florian A1 - Chang, C. F. A1 - Föhlisch, Alexander A1 - Wurth, W. A1 - Metcalf, P. A1 - Leonov, I. A1 - Yaresko, A. A1 - Stojanovic, N. A1 - Berglund, Martin A1 - Guerassimova, N. A1 - Duesterer, S. A1 - Redlin, H. A1 - Duerr, H. A. T1 - Time-resolved resonant soft x-ray diffraction with free-electron lasers femtosecond dynamics across the Verwey transition in magnetite JF - Applied physics letters N2 - Resonant soft x-ray diffraction (RSXD) with femtosecond (fs) time resolution is a powerful tool for disentangling the interplay between different degrees of freedom in strongly correlated electron materials. It allows addressing the coupling of particular degrees of freedom upon an external selective perturbation, e. g., by an optical or infrared laser pulse. Here, we report a time-resolved RSXD experiment from the prototypical correlated electron material magnetite using soft x-ray pulses from the free-electron laser FLASH in Hamburg. We observe ultrafast melting of the charge-orbital order leading to the formation of a transient phase, which has not been observed in equilibrium. Y1 - 2011 U6 - https://doi.org/10.1063/1.3584855 SN - 0003-6951 VL - 98 IS - 18 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Miedema, P. S. A1 - Beye, Martin A1 - Koennecke, R. A1 - Schiwietz, G. A1 - Föhlisch, Alexander T1 - The angular- and crystal-momentum transfer through electron-phonon coupling in silicon and silicon-carbide: similarities and differences JF - New journal of physics : the open-access journal for physics N2 - 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. KW - electron-phonon scattering KW - 6H-SiC KW - RIXS Y1 - 2014 U6 - https://doi.org/10.1088/1367-2630/16/9/093056 SN - 1367-2630 VL - 16 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Wernet, Philippe A1 - Kunnus, Kristjan A1 - Josefsson, Ida A1 - Rajkovic, Ivan A1 - Quevedo, Wilson A1 - Beye, Martin A1 - Schreck, Simon A1 - Gruebel, S. A1 - Scholz, Mirko A1 - Nordlund, Dennis A1 - Zhang, Wenkai A1 - Hartsock, Robert W. A1 - Schlotter, William F. A1 - Turner, Joshua J. A1 - Kennedy, Brian A1 - Hennies, Franz A1 - de Groot, Frank M. F. A1 - Gaffney, Kelly J. A1 - Techert, Simone A1 - Odelius, Michael A1 - Föhlisch, Alexander T1 - Orbital-specific mapping of the ligand exchange dynamics of Fe(CO)(5) in solution JF - Nature : the international weekly journal of science N2 - 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. Y1 - 2015 U6 - https://doi.org/10.1038/nature14296 SN - 0028-0836 SN - 1476-4687 VL - 520 IS - 7545 SP - 78 EP - 81 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Xin, Hong A1 - LaRue, Jerry A1 - Oberg, Henrik A1 - Beye, Martin A1 - Turner, J. J. A1 - Gladh, Jörgen A1 - Ng, May L. A1 - Sellberg, Jonas A. A1 - Kaya, Sarp A1 - Mercurio, G. A1 - Hieke, F. A1 - Nordlund, Dennis A1 - Schlotter, William F. A1 - Dakovski, Georgi L. A1 - Minitti, Michael P. A1 - Föhlisch, Alexander A1 - Wolf, Martin A1 - Wurth, Wilfried A1 - Ogasawara, Hirohito A1 - Norskov, Jens K. A1 - Ostrom, Henrik A1 - Pettersson, Lars G. M. A1 - Nilsson, Anders A1 - Abild-Pedersen, Frank T1 - Strong Influence of Coadsorbate Interaction on CO Desorption Dynamics on Ru(0001) Probed by Ultrafast X-Ray Spectroscopy and Ab Initio Simulations JF - Physical review letters N2 - 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. Y1 - 2015 U6 - https://doi.org/10.1103/PhysRevLett.114.156101 SN - 0031-9007 SN - 1079-7114 VL - 114 IS - 15 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Förster, Daniel F. A1 - Lindenau, Bernd A1 - Leyendecker, Marko A1 - Janssen, Franz A1 - Winkler, Carsten A1 - Schumann, Frank O. A1 - Kirschner, Juergen A1 - Holldack, Karsten A1 - Föhlisch, Alexander T1 - Phase-locked MHz pulse selector for x-ray sources JF - Optics letters : a publication of the Optical Society of America N2 - 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 Y1 - 2015 U6 - https://doi.org/10.1364/OL.40.002265 SN - 0146-9592 SN - 1539-4794 VL - 40 IS - 10 SP - 2265 EP - 2268 PB - Optical Society of America CY - Washington ER - TY - JOUR A1 - Beye, Martin A1 - Föhlisch, Alexander T1 - A soft X-ray approach to electron-phonon interactions beyond the Born-Oppenheimer approximation JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - 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. KW - Electron-phonon coupling KW - Resonant inelastic X-ray scattering KW - X-ray emission spectroscopy KW - Near edge X-ray absorption fine structure Y1 - 2011 U6 - https://doi.org/10.1016/j.elspec.2010.12.032 SN - 0368-2048 VL - 184 IS - 3-6 SP - 313 EP - 317 PB - Elsevier CY - Amsterdam ER - TY - INPR A1 - Föhlisch, Alexander A1 - de Groot, F. M. F. A1 - Odelius, Michael A1 - Techert, Simone A1 - Wernet, P. T1 - Comment on "state-dependent electron delocalization dynamics at the solute-solvent interface: soft-x-ray absorption spectroscopy and lambda b initio calculations" T2 - Physical review letters Y1 - 2014 U6 - https://doi.org/10.1103/PhysRevLett.112.129302 SN - 0031-9007 SN - 1079-7114 VL - 112 IS - 12 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Oberg, H. A1 - Gladh, Jörgen A1 - Anniyev, Toyli A1 - Beye, Martin A1 - Coffee, Ryan A1 - Föhlisch, Alexander A1 - Katayama, T. A1 - Kaya, Sarp A1 - LaRue, Jerry A1 - Mogelhoj, Andreas A1 - Nordlund, Dennis A1 - Ogasawara, Hirohito A1 - Schlotter, William F. A1 - Sellberg, Jonas A. A1 - Sorgenfrei, Florian A1 - Turner, Joshua J. A1 - Wolf, Martin A1 - Wurth, W. A1 - Ostrom, Henrik A1 - Nilsson, Anders A1 - Norskov, Jens K. A1 - Pettersson, Lars G. M. T1 - Optical laser-induced CO desorption from Ru(0001) monitored with a free-electron X-ray laser: DFT prediction and X-ray confirmation of a precursor state JF - Surface science N2 - We present density functional theory modeling of time-resolved optical pump/X-ray spectroscopic probe data of CO desorption from Ru(0001). The BEEF van der Waals functional predicts a weakly bound state as a precursor to desorption. The optical pump leads to a near-instantaneous (<100 fs) increase of the electronic temperature to nearly 7000 K. The temperature evolution and energy transfer between electrons, substrate phonons and adsorbate is described by the two-temperature model and found to equilibrate on a timescale of a few picoseconds to an elevated local temperature of similar to 2000K. Estimating the free energy based on the computed potential of mean force along the desorption path, we find an entropic barrier to desorption (and by time-reversal also to adsorption). This entropic barrier separates the chemisorbed and precursor states, and becomes significant at the elevated temperature of the experiment (similar to 1.4 eV at 2000 K). Experimental pump-probe X-ray absorption/X-ray emission spectroscopy indicates population of a precursor state to desorption upon laser-excitation of the system (Dell'Angela et al., 2013). Computing spectra along the desorption path confirms the picture of a weakly bound transient state arising from ultrafast heating of the metal substrate. (C) 2015 Elsevier B.V. All rights reserved. KW - CO desorption KW - Potential of mean force KW - Two-temperature model KW - Pump-probe KW - X-ray spectroscopy KW - Density functional theory Y1 - 2015 U6 - https://doi.org/10.1016/j.susc.2015.03.011 SN - 0039-6028 SN - 1879-2758 VL - 640 SP - 80 EP - 88 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Kunnus, Kristjan A1 - Schreck, Simon A1 - Föhlisch, Alexander T1 - Free-electron laser based resonant inelastic X-ray scattering on molecules and liquids JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - 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. KW - Free-electron laser KW - RIXS KW - Pump-probe KW - Nonlinear X-ray spectroscopy KW - Molecules KW - Liquids Y1 - 2015 U6 - https://doi.org/10.1016/j.elspec.2015.08.012 SN - 0368-2048 SN - 1873-2526 VL - 204 SP - 345 EP - 355 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Wernet, Philippe A1 - Kunnus, Kristjan A1 - Schreck, Simon A1 - Quevedo, Wilson A1 - Kurian, Reshmi A1 - Techert, Simone A1 - de Groot, Frank M. F. A1 - Odelius, Michael A1 - Föhlisch, Alexander T1 - Dissecting local atomic and intermolecular interactions of transition-metal ions in solution with selective X-ray spectroscopy JF - The journal of physical chemistry letters N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1021/jz301486u SN - 1948-7185 VL - 3 IS - 23 SP - 3448 EP - 3453 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Miedema, Piter S. A1 - Wernet, Philippe A1 - Föhlisch, Alexander T1 - State-dependent fluorescence yields through the core-valence Coulomb exchange parameter JF - Physical review : A, Atomic, molecular, and optical physics N2 - 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. Y1 - 2014 U6 - https://doi.org/10.1103/PhysRevA.89.052507 SN - 1050-2947 SN - 1094-1622 VL - 89 IS - 5 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Thielemann-Kühn, Nele A1 - Hoffmann, P. A1 - Föhlisch, Alexander T1 - A versatile detector for total fluorescence and electron yield experiments JF - Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1063/1.4754126 SN - 0034-6748 VL - 83 IS - 9 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Miedema, Piter Sybren A1 - Beye, Martin A1 - Koennecke, R. A1 - Schiwietz, Gregor A1 - Föhlisch, Alexander T1 - Thermal evolution of the band edges of 6H-SiC: X-ray methods compared to the optical band gap JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - 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. KW - RIXS KW - XAS KW - XES KW - Semiconductors KW - Silicon carbide Y1 - 2014 U6 - https://doi.org/10.1016/j.elspec.2014.08.003 SN - 0368-2048 SN - 1873-2526 VL - 197 SP - 37 EP - 42 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Holldack, Karsten A1 - Ovsyannikov, Ruslan A1 - Kuske, P. A1 - Mueller, R. A1 - Schaelicke, A. A1 - Scheer, M. A1 - Gorgoi, Mihaela A1 - Kuehn, D. A1 - Leitner, T. A1 - Svensson, S. A1 - Martensson, N. A1 - Föhlisch, Alexander T1 - Single bunch X-ray pulses on demand from a multi-bunch synchrotron radiation source JF - Nature Communications N2 - 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. Y1 - 2014 U6 - https://doi.org/10.1038/ncomms5010 SN - 2041-1723 VL - 5 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Kunnus, Kristjan A1 - Josefsson, Ida A1 - Rajkovic, Ivan A1 - Schreck, Simon A1 - Quevedo, Wilson A1 - Beye, Martin A1 - Grübel, Sebastian A1 - Scholz, Mirko A1 - Nordlund, Dennis A1 - Zhang, Wenkai A1 - Hartsock, Robert W. A1 - Gaffney, Kelly J. A1 - Schlotter, William F. A1 - Turner, Joshua J. A1 - Kennedy, Brian A1 - Hennies, Franz A1 - Techert, Simone A1 - Wernet, Philippe A1 - Odelius, Michael A1 - Föhlisch, Alexander T1 - Anti-Stokes resonant x-ray Raman scattering for atom specific and excited state selective dynamics JF - NEW JOURNAL OF PHYSICS N2 - 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. KW - ultrafast photochemistry KW - excited state selectivity KW - anti-Stokes resonant x-ray raman scattering KW - free electron lasers KW - resonant inelastic x-ray scattering Y1 - 2016 U6 - https://doi.org/10.1088/1367-2630/18/10/103011 SN - 1367-2630 VL - 18 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Kunnus, Kristjan A1 - Josefsson, I. A1 - Rajkovic, Ivan A1 - Schreck, Simon A1 - Quevedo, Wilson A1 - Beye, Martin A1 - Weniger, C. A1 - Gruebel, S. A1 - Scholz, M. A1 - Nordlund, D. A1 - Zhang, W. A1 - Hartsock, R. W. A1 - Gaffney, K. J. A1 - Schlotter, W. F. A1 - Turner, J. J. A1 - Kennedy, B. A1 - Hennies, F. A1 - de Groot, F. M. F. A1 - Techert, S. A1 - Odelius, Michael A1 - Wernet, Ph. A1 - Föhlisch, Alexander T1 - Identification of the dominant photochemical pathways and mechanistic insights to the ultrafast ligand exchange of Fe(CO)(5) to Fe(CO)(4)EtOH JF - Structural dynamics N2 - 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). Y1 - 2016 U6 - https://doi.org/10.1063/1.4941602 SN - 2329-7778 VL - 3 PB - American Institute of Physics CY - Washington ER - TY - JOUR A1 - Kunnus, Kristjan A1 - Zhang, Wenkai A1 - Delcey, Mickael G. A1 - Pinjari, Rahul V. A1 - Miedema, Piter S. A1 - Schreck, Simon A1 - Quevedo, Wilson A1 - Schröder, Henning A1 - Föhlisch, Alexander A1 - Gaffney, Kelly J. A1 - Lundberg, Marcus A1 - Odelius, Michael A1 - Wernet, Philippe T1 - Viewing the Valence Electronic Structure of Ferric and Ferrous Hexacyanide in Solution from the Fe and Cyanide Perspectives JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - 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. Y1 - 2016 U6 - https://doi.org/10.1021/acs.jpcb.6b04751 SN - 1520-6106 VL - 120 SP - 7182 EP - 7194 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Dell'Angela, Martina A1 - Anniyev, Toyli A1 - Beye, Martin A1 - Coffee, Ryan A1 - Föhlisch, Alexander A1 - Gladh, Jörgen A1 - Kaya, Sarp A1 - Katayama, Tetsuo A1 - Krupin, Oleg A1 - Nilsson, Anders A1 - Nordlund, Dennis A1 - Schlotter, William F. A1 - Sellberg, Jonas A. A1 - Sorgenfrei, Florian A1 - Turner, Joshua J. A1 - ÖstrÖm, Henrik A1 - Ogasawara, Hirohito A1 - Wolf, Martin A1 - Wurth, Wilfried T1 - Vacuum space charge effects in sub-picosecond soft X-ray photoemission on a molecular adsorbate layer JF - Structural dynamics N2 - Vacuum space charge induced kinetic energy shifts of O 1s and Ru 3d core levels in femtosecond soft X-ray photoemission spectra (PES) have been studied at a free electron laser (FEL) for an oxygen layer on Ru(0001). We fully reproduced the measurements by simulating the in-vacuum expansion of the photoelectrons and demonstrate the space charge contribution of the high-order harmonics in the FEL beam. Employing the same analysis for 400 nm pump-X-ray probe PES, we can disentangle the delay dependent Ru 3d energy shifts into effects induced by space charge and by lattice heating from the femtosecond pump pulse. (C) 2015 Author(s). Y1 - 2015 U6 - https://doi.org/10.1063/1.4914892 SN - 2329-7778 VL - 2 IS - 2 PB - American Institute of Physics CY - Melville ER - TY - BOOK A1 - Föhlisch, Alexander T1 - Phasenübergänge und Ultrakurzzeitdynamik : Antrittsvorlesung 2010-05-12 N2 - Föhlisch wird in seinem Vortrag die großen Zukunftsthemen der Mensch streifen: Energie, Umwelt und Struktur der Materie. Die Komplexität ihrer elementaren Prozesse erfordert die komplementäre Betrachtung der damit verbundene Dimensionen von Energie, Zeit und Raum. Dies lässt sich inzwischen mit Synchrotronstrahlungsquellen in größter Präision darstellen. Y1 - 2010 UR - http://info.ub.uni-potsdam.de/multimedia/show_projekt.php?projekt_id=63 PB - Univ.-Bibl. CY - Potsdam ER - TY - JOUR A1 - Wernet, Philippe A1 - Leitner, T. A1 - Josefsson, Ida A1 - Mazza, T. A1 - Miedema, P. S. A1 - Schroder, H. A1 - Beye, Martin A1 - Kunnus, K. A1 - Schreck, S. A1 - Radcliffe, P. A1 - Dusterer, S. A1 - Meyer, M. A1 - Odelius, Michael A1 - Fohlisch, Alexander T1 - Communication: Direct evidence for sequential dissociation of gas-phase Fe(CO)(5) via a singlet pathway upon excitation at 266 nm JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - 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. Y1 - 2017 U6 - https://doi.org/10.1063/1.4984774 SN - 0021-9606 SN - 1089-7690 VL - 146 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Niskanen, Johannes A1 - Jankala, Kari A1 - Huttula, Marco A1 - Föhlisch, Alexander T1 - QED effects in 1s and 2s single and double ionization potentials of the noble gases JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - 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. Y1 - 2017 U6 - https://doi.org/10.1063/1.4979991 SN - 0021-9606 SN - 1089-7690 VL - 146 SP - 1443 EP - 1450 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Niskanen, Johannes A1 - Sahle, Christoph J. A1 - Gilmore, Keith A1 - Uhlig, Frank A1 - Smiatek, Jens A1 - Föhlisch, Alexander T1 - Disentangling structural information from core-level excitation spectra JF - Physical review : E, Statistical, nonlinear and soft matter physics N2 - 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. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevE.96.013319 SN - 2470-0045 SN - 2470-0053 VL - 96 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Cappel, Ute B. A1 - Svanstrom, Sebastian A1 - Lanzilotto, Valeria A1 - Johansson, Fredrik O. L. A1 - Aitola, Kerttu A1 - Philippe, Bertrand A1 - Giangrisostomi, Erika A1 - Ovsyannikov, Ruslan A1 - Leitner, Torsten A1 - Föhlisch, Alexander A1 - Svensson, Svante A1 - Martensson, Nils A1 - Boschloo, Gerrit A1 - Lindblad, Andreas A1 - Rensmo, Hakan T1 - Partially Reversible Photoinduced Chemical Changes in a Mixed-Ion Perovskite Material for Solar Cells JF - ACS applied materials & interfaces N2 - 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. KW - photoelectron spectroscopy KW - laser illumination KW - lead halide perovskite KW - ion migration KW - phase separation KW - stability Y1 - 2017 U6 - https://doi.org/10.1021/acsami.7b10643 SN - 1944-8244 VL - 9 SP - 34970 EP - 34978 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Haverkamp, Robert A1 - Sorgenfrei, Nomi L. A. N. A1 - Giangrisostomi, Erika A1 - Neppl, Stefan A1 - Kühn, Danilo A1 - Föhlisch, Alexander T1 - Directional charge delocalization dynamics in semiconducting 2H-MoS2 and metallic 1T-LixMoS2 JF - Scientific reports N2 - The layered dichalcogenide MoS2 is relevant for electrochemical Li adsorption/intercalation, in the course of which the material undergoes a concomitant structural phase transition from semiconducting 2H-MoS2 to metallic 1T-LixMoS2. With the core hole clock approach at the S L1 X-ray absorption edge we quantify the ultrafast directional charge transfer of excited S3p electrons in-plane () and out-of-plane (perpendicular to) for 2H-MoS2 as tau 2H,=0.38 +/- 0.08 fs and tau 2H,perpendicular to =0.33 +/- 0.06 fs and for 1T-LixMoS2 as tau 1T,=0.32 +/- 0.12 fs and tau 1T,perpendicular to =0.09 +/- 0.07 fs. The isotropic charge delocalization of S3p electrons in the semiconducting 2H phase within the S-Mo-S sheets is assigned to the specific symmetry of the Mo-S bonding arrangement. Formation of 1T-LixMoS2 by lithiation accelerates the in-plane charge transfer by a factor of similar to 1.2 due to electron injection to the Mo-S covalent bonds and concomitant structural repositioning of S atoms within the S-Mo-S sheets. For excitation into out-of-plane orbitals, an accelerated charge transfer by a factor of similar to 3.7 upon lithiation occurs due to S-Li coupling. Y1 - 2021 U6 - https://doi.org/10.1038/s41598-021-86364-2 SN - 2045-2322 VL - 11 IS - 1 PB - Macmillan Publishers Limited, part of Springer Nature CY - London ER - TY - JOUR A1 - Beye, Martin A1 - Öberg, Henrik A1 - Xin, Hongliang A1 - Dakovski, Georgi L. A1 - Föhlisch, Alexander A1 - Gladh, Jorgen A1 - Hantschmann, Markus A1 - Hieke, Florian A1 - Kaya, Sarp A1 - Kühn, Danilo A1 - LaRue, Jerry A1 - Mercurio, Giuseppe A1 - Minitti, Michael P. A1 - Mitra, Ankush A1 - Moeller, Stefan P. A1 - Ng, May Ling A1 - Nilsson, Anders A1 - Nordlund, Dennis A1 - Norskov, Jens A1 - Öström, Henrik A1 - Ogasawara, Hirohito A1 - Persson, Mats A1 - Schlotter, William F. A1 - Sellberg, Jonas A. A1 - Wolf, Martin A1 - Abild-Pedersen, Frank A1 - Pettersson, Lars G. M. A1 - Wurth, Wilfried T1 - Chemical Bond Activation Observed with an X-ray Laser JF - The journal of physical chemistry letters N2 - 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. Y1 - 2016 U6 - https://doi.org/10.1021/acs.jpclett.6b01543 SN - 1948-7185 VL - 7 SP - 3647 EP - 3651 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Ostrom, H. A1 - Oberg, H. A1 - Xin, H. A1 - Larue, J. A1 - Beye, Martin A1 - Gladh, J. A1 - Ng, M. L. A1 - Sellberg, J. A. A1 - Kaya, S. A1 - Mercurio, G. A1 - Nordlund, D. A1 - Hantschmann, Markus A1 - Hieke, F. A1 - Kuehn, D. A1 - Schlotter, W. F. A1 - Dakovski, G. L. A1 - Turner, J. J. A1 - Minitti, M. P. A1 - Mitra, A. A1 - Moeller, S. P. A1 - Föhlisch, Alexander A1 - Wolf, M. A1 - Wurth, W. A1 - Persson, Mats A1 - Norskov, J. K. A1 - Abild-Pedersen, Frank A1 - Ogasawara, Hirohito A1 - Pettersson, Lars G. M. A1 - Nilsson, A. T1 - Probing the transition state region in catalytic CO oxidation on Ru JF - Science N2 - 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. Y1 - 2015 U6 - https://doi.org/10.1126/science.1261747 SN - 0036-8075 SN - 1095-9203 VL - 347 IS - 6225 SP - 978 EP - 982 PB - American Assoc. for the Advancement of Science CY - Washington ER - TY - JOUR A1 - Hantschmann, Markus A1 - Föhlisch, Alexander T1 - A rate model approach for FEL pulse induced transmissions changes, saturable absorption, X-ray transparency and stimulated emission JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - 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. KW - Free-electron-laser science KW - RIXS at FELs KW - Stimulated scattering KW - Pulse induced transparency KW - Scattering breakdown Y1 - 2022 U6 - https://doi.org/10.1016/j.elspec.2021.147139 SN - 0368-2048 VL - 256 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Martensson, Nils A1 - Föhlisch, Alexander A1 - Svensson, Svante T1 - Uppsala and Berkeley BT - two essential laboratories in the development of modern photoelectron spectroscopy JF - Journal of vacuum science & technology : JVST ; an AVS journal / A N2 - 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. KW - Electronic structure KW - Condensed matter physics KW - X-ray emission spectroscopy KW - Electron spectroscopy KW - Photoelectron spectroscopy KW - Nuclear physics KW - Storage rings KW - Synchrotron radiation KW - Gas phase KW - Surface science Y1 - 2022 U6 - https://doi.org/10.1116/6.0001879 SN - 0734-2101 SN - 1520-8559 VL - 40 IS - 4 PB - American Institute of Physics CY - New York ER - TY - JOUR A1 - Sun, Y. -P. A1 - Hennies, Franz A1 - Pietzsch, Annette A1 - Kennedy, B. A1 - Schmitt, Thorsten A1 - Strocov, Vladimir N. A1 - Andersson, Joakim A1 - Berglund, Martin A1 - Rubensson, Jan-Erik A1 - Aidas, K. A1 - Gel'mukhanov, F. A1 - Odelius, Michael A1 - Föhlisch, Alexander T1 - Intramolecular soft modes and intermolecular interactions in liquid acetone JF - Physical review : B, Condensed matter and materials physics N2 - 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. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevB.84.132202 SN - 1098-0121 VL - 84 IS - 13 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Kubin, Markus A1 - Guo, Meiyuan A1 - Kroll, Thomas A1 - Loechel, Heike A1 - Kallman, Erik A1 - Baker, Michael L. A1 - Mitzner, Rolf A1 - Gul, Sheraz A1 - Kern, Jan A1 - Föhlisch, Alexander A1 - Erko, Alexei A1 - Bergmann, Uwe A1 - Yachandra, Vittal A1 - Yano, Junko A1 - Lundberg, Marcus A1 - Wernet, Philippe T1 - Probing the oxidation state of transition metal complexes BT - a case study on how charge and spin densities determine Mn L-edge X-ray absorption energies JF - Chemical science N2 - 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. Y1 - 2018 U6 - https://doi.org/10.1039/c8sc00550h SN - 2041-6520 SN - 2041-6539 VL - 9 IS - 33 SP - 6813 EP - 6829 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Giangrisostomi, Erika A1 - Ovsyannikov, Ruslan A1 - Sorgenfrei, Florian A1 - Zhang, Teng A1 - Lindblad, Andreas A1 - Sassa, Yasmine A1 - Cappel, Ute B. A1 - Leitner, Torsten A1 - Mitzner, Rolf A1 - Svensson, Svante A1 - Martensson, Nils A1 - Föhlisch, Alexander T1 - Low Dose Photoelectron Spectroscopy at BESSY II BT - electronic structure of matter in its native state JF - Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy N2 - The implementation of a high-transmission, angular-resolved time-of-Right electron spectrometer with a 1.25 MHz pulse selector at the PM4 soft X-ray dipole beamline of the synchrotron BESSY II creates unique capabilities to inquire electronic structure via photoelectron spectroscopy with a minimum of radiation dose. Solid-state samples can be prepared and characterized with standard UHV techniques and rapidly transferred from various preparation chambers to a 4-axis temperature-controlled measurement stage. A synchronized MHz laser system enables excited-state characterization and dynamical studies starting from the picosecond timescale. This article introduces the principal characteristics of the PM4 beamline and LowDosePES end-station. Recent results from graphene, an organic hole transport material for solar cells and the transition metal dichalcogenide MoS2 are presented to demonstrate the instrument performances. Y1 - 2018 U6 - https://doi.org/10.1016/j.elspec.2017.05.011 SN - 0368-2048 SN - 1873-2526 VL - 224 SP - 68 EP - 78 PB - Elsevier CY - Amsterdam ER - TY - GEN A1 - Niskanen, Johannes A1 - Kooser, Kuno A1 - Koskelo, Jaakko A1 - Käämbre, Tanel A1 - Kunnus, Kristjan A1 - Pietzsch, Annette A1 - Quevedo, Wilson A1 - Hakala, Mikko A1 - Föhlisch, Alexander A1 - Huotari, Simo A1 - Kukk, Edwin T1 - Density functional simulation of resonant inelastic X-ray scattering experiments in liquids: acetonitrile N2 - 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 331 Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-395133 ER - TY - JOUR A1 - Yin, Zhong A1 - Rajkovic, Ivan A1 - Veedu, Sreevidya Thekku A1 - Deinert, Sascha A1 - Raiser, Dirk A1 - Jain, Rohit A1 - Fukuzawa, Hironobu A1 - Wada, Shin-ichi A1 - Quevedo, Wilson A1 - Kennedy, Brian A1 - Schreck, Simon A1 - Pietzsch, Annette A1 - Wernet, Philippe A1 - Ueda, Kyoshi A1 - Föhlisch, Alexander A1 - Techert, Simone T1 - Ionic solutions probed by resonant inelastic X-ray scattering JF - Zeitschrift für physikalische Chemie : international journal of research in physical chemistry and chemical physics N2 - 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. KW - X-ray Spectroscopy KW - XAS KW - XES KW - RIXS KW - Anions KW - Cations KW - Liquid Jet KW - Synchrotron Radiation Y1 - 2015 U6 - https://doi.org/10.1515/zpch-2015-0610 SN - 0942-9352 VL - 229 IS - 10-12 SP - 1855 EP - 1867 PB - De Gruyter CY - Berlin ER - TY - JOUR A1 - Decker, Regis A1 - Born, Artur A1 - Ruotsalainen, Kari A1 - Bauer, Karl A1 - Haverkamp, Robert A1 - Büchner, Robby A1 - Pietzsch, Annette A1 - Föhlisch, Alexander T1 - Spin-lattice angular momentum transfer of localized and valence electrons in the demagnetization transient state of gadolinium JF - Applied physics letters N2 - 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. Y1 - 2021 U6 - https://doi.org/10.1063/5.0063404 SN - 0003-6951 SN - 1077-3118 VL - 119 IS - 15 PB - AIP Publishing CY - Melville ER - TY - GEN A1 - Kubin, Markus A1 - Guo, Meiyuan A1 - Kroll, Thomas A1 - Löchel, Heike A1 - Källman, Erik A1 - Baker, Michael L. A1 - Mitzner, Rolf A1 - Gul, Sheraz A1 - Kern, Jan A1 - Föhlisch, Alexander A1 - Erko, Alexei A1 - Bergmann, Uwe A1 - Yachandra, Vittal A1 - Yano, Junko A1 - Lundberg, Marcus A1 - Wernet, Philippe T1 - Probing the oxidation state of transition metal complexes BT - a case study on how charge and spin densities determine Mn L-edge X-ray absorption energies T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 656 KW - electronic-structure KW - atomic multiplet KW - water-oxidation KW - iron complexes KW - photosystem-II KW - spectroscopy KW - manganese KW - spectra KW - ligand KW - FE Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-425057 SN - 1866-8372 IS - 656 ER - TY - JOUR A1 - Pietzsch, Annette A1 - Sun, Y. -P. A1 - Hennies, Franz A1 - Rinkevicius, Z. A1 - Karlsson, Hans O. A1 - Schmitt, Thorsten A1 - Strocov, Vladimir N. A1 - Andersson, Joakim A1 - Kennedy, B. A1 - Schlappa, J. A1 - Föhlisch, Alexander A1 - Rubensson, Jan-Erik A1 - Gel'mukhanov, F. T1 - Spatial quantum beats in vibrational resonant inelastic soft X-ray scattering at dissociating states in oxygen JF - Physical review letters N2 - 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. Y1 - 2011 U6 - https://doi.org/10.1103/PhysRevLett.106.153004 SN - 0031-9007 VL - 106 IS - 15 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Pietzsch, Annette A1 - Hennies, Franz A1 - Miedema, Piter S. A1 - Kennedy, Brian A1 - Schlappa, Justine A1 - Schmitt, Thorsten A1 - Strocov, Vladimir N. A1 - Föhlisch, Alexander T1 - Snapshots of the Fluctuating Hydrogen Bond Network in Liquid Water on the Sub-Femtosecond Timescale with Vibrational Resonant Inelastic x-ray Scattering JF - Physical review letters N2 - 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. Y1 - 2015 U6 - https://doi.org/10.1103/PhysRevLett.114.088302 SN - 0031-9007 SN - 1079-7114 VL - 114 IS - 8 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Kubin, Markus A1 - Kern, Jan A1 - Gul, Sheraz A1 - Kroll, Thomas A1 - Chatterjee, Ruchira A1 - Loechel, Heike A1 - Fuller, Franklin D. A1 - Sierra, Raymond G. A1 - Quevedo, Wilson A1 - Weniger, Christian A1 - Rehanek, Jens A1 - Firsov, Anatoly A1 - Laksmono, Hartawan A1 - Weninger, Clemens A1 - Alonso-Mori, Roberto A1 - Nordlund, Dennis L. A1 - Lassalle-Kaiser, Benedikt A1 - Glownia, James M. A1 - Krzywinski, Jacek A1 - Moeller, Stefan A1 - Turner, Joshua J. A1 - Minitti, Michael P. A1 - Dakovski, Georgi L. A1 - Koroidov, Sergey A1 - Kawde, Anurag A1 - Kanady, Jacob S. A1 - Tsui, Emily Y. A1 - Suseno, Sandy A1 - Han, Zhiji A1 - Hill, Ethan A1 - Taguchi, Taketo A1 - Borovik, Andrew S. A1 - Agapie, Theodor A1 - Messinger, Johannes A1 - Erko, Alexei A1 - Föhlisch, Alexander A1 - Bergmann, Uwe A1 - Mitzner, Rolf A1 - Yachandra, Vittal K. A1 - Yano, Junko A1 - Wernet, Philippe T1 - Soft x-ray absorption spectroscopy of metalloproteins and high-valent metal-complexes at room temperature using free-electron lasers JF - Structural dynamics N2 - 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). Y1 - 2017 U6 - https://doi.org/10.1063/1.4986627 SN - 2329-7778 VL - 4 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Liu, Chun-Yu A1 - Ruotsalainen, Kari A1 - Bauer, Karl A1 - Decker, Régis A1 - Pietzsch, Annette A1 - Föhlisch, Alexander T1 - Excited-state exchange interaction in NiO determined by high-resolution resonant inelastic x-ray scattering at the Ni M2,3 edges JF - Physical review : B, Condensed matter and materials physics N2 - 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. Y1 - 2022 U6 - https://doi.org/10.1103/PhysRevB.106.035104 SN - 2469-9950 SN - 2469-9969 VL - 106 IS - 3 PB - American Physical Society CY - Ridge, NY ER - TY - JOUR A1 - Born, Artur A1 - Decker, Regis A1 - Haverkamp, Robert A1 - Ruotsalainen, Kari A1 - Bauer, Karl A1 - Pietzsch, Annette A1 - Föhlisch, Alexander A1 - Büchner, Robby T1 - Thresholding of the Elliott-Yafet spin-flip scattering in multi-sublattice magnets by the respective exchange energies JF - Scientific reports N2 - 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. Y1 - 2021 U6 - https://doi.org/10.1038/s41598-021-81177-9 SN - 2045-2322 VL - 11 IS - 1 PB - Springer Nature CY - Berlin ER - TY - JOUR A1 - Kroll, Thomas A1 - Kern, Jan A1 - Kubin, Markus A1 - Ratner, Daniel A1 - Gul, Sheraz A1 - Fuller, Franklin D. A1 - Löchel, Heike A1 - Krzywinski, Jacek A1 - Lutman, Alberto A1 - Ding, Yuantao A1 - Dakovski, Georgi L. A1 - Moeller, Stefan A1 - Turner, Joshua J. A1 - Alonso-Mori, Roberto A1 - Nordlund, Dennis L. A1 - Rehanek, Jens A1 - Weniger, Christian A1 - Firsov, Alexander A1 - Brzhezinskaya, Maria A1 - Chatterjee, Ruchira A1 - Lassalle-Kaiser, Benedikt A1 - Sierra, Raymond G. A1 - Laksmono, Hartawan A1 - Hill, Ethan A1 - Borovik, Andrew S. A1 - Erko, Alexei A1 - Föhlisch, Alexander A1 - Mitzner, Rolf A1 - Yachandra, Vittal K. A1 - Yano, Junko A1 - Wernet, Philippe A1 - Bergmann, Uwe T1 - X-ray absorption spectroscopy using a self-seeded soft X-ray free-electron laser JF - Optics express : the international electronic journal of optics N2 - 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 Y1 - 2016 U6 - https://doi.org/10.1364/OE.24.022469 SN - 1094-4087 VL - 24 SP - 22469 EP - 22480 PB - Optical Society of America CY - Washington ER - TY - JOUR A1 - Mitzner, Rolf A1 - Rehanek, Jens A1 - Kern, Jan A1 - Gul, Sheraz A1 - Hattne, Johan A1 - Taguchi, Taketo A1 - Alonso-Mori, Roberto A1 - Tran, Rosalie A1 - Weniger, Christian A1 - Schröder, Henning A1 - Quevedo, Wilson A1 - Laksmono, Hartawan A1 - Sierra, Raymond G. A1 - Han, Guangye A1 - Lassalle-Kaiser, Benedikt A1 - Koroidov, Sergey A1 - Kubicek, Katharina A1 - Schreck, Simon A1 - Kunnus, Kristjan A1 - Brzhezinskaya, Maria A1 - Firsov, Alexander A1 - Minitti, Michael P. A1 - Turner, Joshua J. A1 - Möller, Stefan A1 - Sauter, Nicholas K. A1 - Bogan, Michael J. A1 - Nordlund, Dennis A1 - Schlotter, William F. A1 - Messinger, Johannes A1 - Borovik, Andrew S. A1 - Techert, Simone A1 - de Groot, Frank M. F. A1 - Föhlisch, Alexander A1 - Erko, Alexei A1 - Bergmann, Uwe A1 - Yachandra, Vittal K. A1 - Wernet, Philippe A1 - Yano, Junko T1 - L-edge x-ray absorption spectroscopy of dilute systems relevant to metalloproteins using an X-ray free-electron laser JF - The journal of physical chemistry letters N2 - 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. Y1 - 2013 U6 - https://doi.org/10.1021/jz401837f SN - 1948-7185 VL - 4 IS - 21 SP - 3641 EP - 3647 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Arhammar, C. A1 - Pietzsch, Annette A1 - Bock, Nicolas A1 - Holmstroem, Erik A1 - Araujo, C. Moyses A1 - Grasjo, Johan A1 - Zhao, Shuxi A1 - Green, Sara A1 - Peery, T. A1 - Hennies, Franz A1 - Amerioun, Shahrad A1 - Föhlisch, Alexander A1 - Schlappa, Justine A1 - Schmitt, Thorsten A1 - Strocov, Vladimir N. A1 - Niklasson, Gunnar A. A1 - Wallace, Duane C. A1 - Rubensson, Jan-Erik A1 - Johansson, Borje A1 - Ahuja, Rajeev C. T1 - Unveiling the complex electronic structure of amorphous metal oxides JF - Proceedings of the National Academy of Sciences of the United States of America N2 - 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. KW - stochastic quench KW - X-ray absorption spectroscopy KW - ab initio KW - coating Y1 - 2011 U6 - https://doi.org/10.1073/pnas.1019698108 SN - 0027-8424 VL - 108 IS - 16 SP - 6355 EP - 6360 PB - National Acad. of Sciences CY - Washington ER - TY - JOUR A1 - Eschenlohr, Andrea A1 - Battiato, M. A1 - Maldonado, R. A1 - Pontius, N. A1 - Kachel, T. A1 - Holldack, K. A1 - Mitzner, Rolf A1 - Föhlisch, Alexander A1 - Oppeneer, P. M. A1 - Stamm, C. T1 - Ultrafast spin transport as key to femtosecond demagnetization JF - Nature materials N2 - Irradiating a ferromagnet with a femtosecond laser pulse is known to induce an ultrafast demagnetization within a few hundred femtoseconds. Here we demonstrate that direct laser irradiation is in fact not essential for ultrafast demagnetization, and that electron cascades caused by hot electron currents accomplish it very efficiently. We optically excite a Au/Ni layered structure in which the 30 nm Au capping layer absorbs the incident laser pump pulse and subsequently use the X-ray magnetic circular dichroism technique to probe the femtosecond demagnetization of the adjacent 15 nm Ni layer. A demagnetization effect corresponding to the scenario in which the laser directly excites the Ni film is observed, but with a slight temporal delay. We explain this unexpected observation by means of the demagnetizing effect of a superdiffusive current of non-equilibrium, non-spin-polarized electrons generated in the Au layer. Y1 - 2013 U6 - https://doi.org/10.1038/NMAT3546 SN - 1476-1122 VL - 12 IS - 4 SP - 332 EP - 336 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Sun, Y. -P. A1 - Miao, Q. A1 - Pietzsch, Annette A1 - Hennies, F. A1 - Schmitt, T. A1 - Strocov, V. N. A1 - Andersson, Joakim A1 - Kennedy, B. A1 - Schlappa, J. A1 - Föhlisch, Alexander A1 - Gel&rsquo, A1 - mukhanov, F. A1 - Rubensson, J. -E. T1 - Interference between Resonant and Nonresonant Inelastic X-Ray Scattering JF - PHYSICAL REVIEW LETTERS N2 - 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. Y1 - 2013 U6 - https://doi.org/10.1103/PhysRevLett.110.223001 SN - 0031-9007 VL - 110 IS - 22 PB - AMER PHYSICAL SOC CY - COLLEGE PK ER - TY - JOUR A1 - Sun, Y-P A1 - Pietzsch, Annette A1 - Hennies, Franz A1 - Rinkevicius, Z. A1 - Karlsson, Hans O. A1 - Schmitt, Thorsten A1 - Strocov, Vladimir N. A1 - Andersson, Joakim A1 - Kennedy, B. A1 - Schlappa, J. A1 - Föhlisch, Alexander A1 - Gel'mukhanov, F. A1 - Rubensson, Jan-Erik T1 - Internal symmetry and selection rules in resonant inelastic soft x-ray scattering JF - Journal of physics : B, Atomic, molecular and optical physics N2 - 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. Y1 - 2011 U6 - https://doi.org/10.1088/0953-4075/44/16/161002 SN - 0953-4075 VL - 44 IS - 16 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Hennies, Franz A1 - Pietzsch, Annette A1 - Berglund, Martin A1 - Föhlisch, Alexander A1 - Schmitt, Thorsten A1 - Strocov, Vladimir A1 - Karlsson, Hans O. A1 - Andersson, Joakim A1 - Rubensson, Jan-Erik T1 - Resonant inelastic scattering spectra of free molecules with vibrational resolution N2 - 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. Y1 - 2010 UR - http://prl.aps.org/ U6 - https://doi.org/10.1103/Physrevlett.104.193002 SN - 0031-9007 ER - TY - JOUR A1 - Schreck, Simon A1 - Pietzsch, Annette A1 - Kunnus, Kristjan A1 - Kennedy, Brian A1 - Quevedo, Wilson A1 - Miedema, Piter S. A1 - Wernet, Philippe A1 - Föhlisch, Alexander T1 - Dynamics of the OH group and the electronic structure of liquid alcohols JF - Structural dynamics N2 - 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. Y1 - 2014 U6 - https://doi.org/10.1063/1.4897981 SN - 2329-7778 VL - 1 IS - 5 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Schick, Daniel A1 - Le Guyader, Loic A1 - Pontius, Niko A1 - Radu, Ilie A1 - Kachel, Torsten A1 - Mitzner, Rolf A1 - Zeschke, Thomas A1 - Schuessler-Langeheine, Christian A1 - Föhlisch, Alexander A1 - Holldack, Karsten T1 - Analysis of the halo background in femtosecond slicing experiments JF - Journal of synchrotron radiation N2 - 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. KW - femtosecond slicing KW - halo KW - pump-probe KW - XMCD KW - X-ray scattering Y1 - 2016 U6 - https://doi.org/10.1107/S160057751600401X SN - 1600-5775 VL - 23 SP - 700 EP - 711 PB - International Union of Crystallography CY - Chester ER - TY - JOUR A1 - Rubensson, Jan-Erik A1 - Soderstrom, Johan A1 - Binggeli, Christian A1 - Grasjo, Joakim A1 - Andersson, Johan A1 - Sathe, Conny A1 - Hennies, Franz A1 - Bisogni, Valentina A1 - Huang, Yaobo A1 - Olalde, Paul A1 - Schmitt, Thorsten A1 - Strocov, Vladimir N. A1 - Föhlisch, Alexander A1 - Kennedy, Brian A1 - Pietzsch, Annette T1 - Rydberg-Resolved Resonant Inelastic Soft X-Ray Scattering: Dynamics at Core Ionization Thresholds JF - Physical review letters N2 - 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. Y1 - 2015 U6 - https://doi.org/10.1103/PhysRevLett.114.133001 SN - 0031-9007 SN - 1079-7114 VL - 114 IS - 13 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Yin, Zhong A1 - Rajkovic, Ivan A1 - Kubicek, Katharina A1 - Quevedo, Wilson A1 - Pietzsch, Annette A1 - Wernet, Philippe A1 - Föhlisch, Alexander A1 - Techert, Simone T1 - Probing the Hofmeister effect with ultrafast core-hole spectroscopy JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - 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. Y1 - 2014 U6 - https://doi.org/10.1021/jp504577a SN - 1520-6106 VL - 118 IS - 31 SP - 9398 EP - 9403 PB - American Chemical Society CY - Washington ER - TY - GEN A1 - Eschenlohr, Andrea A1 - Battiato, Mario A1 - Maldonado, P. A1 - Pontius, N. A1 - Kachel, T. A1 - Holldack, K. A1 - Mitzner, Rolf A1 - Föhlisch, Alexander A1 - Oppeneer, P. M. A1 - Stamm, Christian T1 - Optical excitation of thin magnetic layers in multilayer structures Reply T2 - Nature materials Y1 - 2014 U6 - https://doi.org/10.1038/nmat3851 SN - 1476-1122 SN - 1476-4660 VL - 13 IS - 2 SP - 102 EP - 103 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Yin, Zhong A1 - Inhester, Ludger A1 - Veedu, Sreevidya Thekku A1 - Quevedo, Wilson A1 - Pietzsch, Annette A1 - Wernet, Philippe A1 - Groenhof, Gerrit A1 - Föhlisch, Alexander A1 - Grubmueller, Helmut A1 - Techert, Simone T1 - Cationic and Anionic Impact on the Electronic Structure of Liquid Water JF - The journal of physical chemistry letters N2 - 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. Y1 - 2017 U6 - https://doi.org/10.1021/acs.jpclett.7b01392 SN - 1948-7185 VL - 8 SP - 3759 EP - 3764 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schreck, Simon A1 - Pietzsch, Annette A1 - Kennedy, Brian A1 - Sathe, Conny A1 - Miedema, Piter S. A1 - Techert, Simone A1 - Strocov, Vladimir N. A1 - Schmitt, Thorsten A1 - Hennies, Franz A1 - Rubensson, Jan-Erik A1 - Föhlisch, Alexander T1 - Ground state potential energy surfaces around selected atoms from resonant inelastic x-ray scattering JF - Scientific reports N2 - 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. Y1 - 2016 U6 - https://doi.org/10.1038/srep20054 SN - 2045-2322 VL - 6 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Thielemann-Kühn, Nele A1 - Schick, Daniel A1 - Pontius, Niko A1 - Trabant, Christoph A1 - Mitzner, Rolf A1 - Holldack, Karsten A1 - Zabel, Hartmut A1 - Föhlisch, Alexander A1 - Schuessler-Langeheine, Christian T1 - Ultrafast and Energy-Efficient Quenching of Spin Order: Antiferromagnetism Beats Ferromagnetism JF - Physical review letters N2 - 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. Y1 - 2017 U6 - https://doi.org/10.1103/PhysRevLett.119.197202 SN - 0031-9007 SN - 1079-7114 VL - 119 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Miedema, P. S. A1 - Mitzner, Rolf A1 - Ganschow, S. A1 - Föhlisch, Alexander A1 - Beye, Martin T1 - X-ray spectroscopy on the active ion in laser crystals JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - 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. Y1 - 2017 U6 - https://doi.org/10.1039/c7cp03026f SN - 1463-9076 SN - 1463-9084 VL - 19 SP - 21800 EP - 21806 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Decker, Régis A1 - Born, Artur A1 - Büchner, Robby A1 - Ruotsalainen, Kari A1 - Stråhlman, Christian A1 - Neppl, Stefan A1 - Haverkamp, Robert A1 - Pietzsch, Annette A1 - Föhlisch, Alexander T1 - Measuring the atomic spin-flip scattering rate by x-ray emission spectroscopy JF - Scientific reports N2 - 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. Y1 - 2019 U6 - https://doi.org/10.1038/s41598-019-45242-8 SN - 2045-2322 VL - 9 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Liu, Ji-Cai A1 - Vaz da Cruz, Vinicius A1 - Polyutov, Sergey A1 - Föhlisch, Alexander T1 - Recoil-induced dissociation in hard-x-ray photoionization JF - Physical review : A, Atomic, molecular, and optical physics N2 - 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. Y1 - 2019 U6 - https://doi.org/10.1103/PhysRevA.100.053408 SN - 2469-9926 SN - 2469-9934 VL - 100 IS - 5 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Pontius, Niko A1 - Beye, Martin A1 - Trabant, Christoph A1 - Mitzner, Rolf A1 - Sorgenfrei, Florian A1 - Kachel, Torsten A1 - Woestmann, Michael A1 - Roling, Sebastian A1 - Zacharias, Helmut A1 - Ivanov, Rosen A1 - Treusch, Rolf A1 - Buchholz, Marcel A1 - Metcalf, Pete A1 - Schuessler-Langeheine, Christian A1 - Föhlisch, Alexander T1 - Probing the non-equilibrium transient state in magnetite by a jitter-free two-color X-ray pump and X-ray probe experiment JF - Structural dynamics N2 - We present a general experimental concept for jitter-free pump and probe experiments at free electron lasers. By generating pump and probe pulse from one and the same X-ray pulse using an optical split-and-delay unit, we obtain a temporal resolution that is limited only by the X-ray pulse lengths. In a two-color X-ray pump and X-ray probe experiment with sub 70 fs temporal resolution, we selectively probe the response of orbital and charge degree of freedom in the prototypical functional oxide magnetite after photoexcitation. We find electronic order to be quenched on a time scale of (30 +/- 30) fs and hence most likely faster than what is to be expected for any lattice dynamics. Our experimental result hints to the formation of a short lived transient state with decoupled electronic and lattice degree of freedom in magnetite. The excitation and relaxation mechanism for X-ray pumping is discussed within a simple model leading to the conclusion that within the first 10 fs the original photoexcitation decays into low-energy electronic excitations comparable to what is achieved by optical pump pulse excitation. Our findings show on which time scales dynamical decoupling of degrees of freedom in functional oxides can be expected and how to probe this selectively with soft X-ray pulses. Results can be expected to provide crucial information for theories for ultrafast behavior of materials and help to develop concepts for novel switching devices. (C) 2018 Author(s). Y1 - 2018 U6 - https://doi.org/10.1063/1.5042847 SN - 2329-7778 VL - 5 IS - 5 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Büchner, Robby A1 - Fondell, Mattis A1 - Mascarenhas, Eric Johnn A1 - Pietzsch, Annette A1 - Vaz da Cruz, Vinícius A1 - Föhlisch, Alexander T1 - How hydrogen bonding amplifies isomeric differences in pyridones toward strong changes in acidity and tautomerism JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - 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. Y1 - 2021 U6 - https://doi.org/10.1021/acs.jpcb.0c10873 SN - 1520-6106 SN - 1520-5207 VL - 125 IS - 9 SP - 2372 EP - 2379 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Büchner, Robby A1 - Fondell, Mattis A1 - Haverkamp, Robert A1 - Pietzsch, Annette A1 - Vaz da Cruz, Vinícius A1 - Föhlisch, Alexander T1 - The porphyrin center as a regulator for metal-ligand covalency and pi hybridization in the entire molecule JF - Physical chemistry, chemical physics : PCCP ; a journal of European Chemical Societies N2 - 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. Y1 - 2021 U6 - https://doi.org/10.1039/d1cp03944j SN - 1463-9076 SN - 1463-9084 VL - 23 IS - 43 SP - 24765 EP - 24772 PB - Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Eckert, Sebastian A1 - Norell, Jesper A1 - Miedema, Piter S. A1 - Beye, Martin A1 - Fondell, Mattis A1 - Quevedo, Wilson A1 - Kennedy, Brian A1 - Hantschmann, Markus A1 - Pietzsch, Annette A1 - van Kuiken, Benjamin E. A1 - Ross, Matthew A1 - Minitti, Michael P. A1 - Moeller, Stefan P. A1 - Schlotter, William F. A1 - Khalil, Munira A1 - Odelius, Michael A1 - Föhlisch, Alexander T1 - Untersuchung unabhängiger N‐H‐ und N‐C‐Bindungsverformungen auf ultrakurzen Zeitskalen mit resonanter inelastischer Röntgenstreuung T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Die Femtosekundendynamik nach resonanten Photoanregungen mit optischen und Röntgenpulsen ermöglicht eine selektive Verformung von chemischen N‐H‐ und N‐C‐Bindungen in 2‐Thiopyridon in wässriger Lösung. Die Untersuchung der orbitalspezifischen elektronischen Struktur und ihrer Dynamik auf ultrakurzen Zeitskalen mit resonanter inelastischer Röntgenstreuung an der N1s‐Resonanz am Synchrotron und dem Freie‐Elektronen‐Laser LCLS in Kombination mit quantenchemischen Multikonfigurationsberechnungen erbringen den direkten Nachweis dieser kontrollierten photoinduzierten Molekülverformungen und ihrer ultrakurzen Zeitskala. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1121 KW - Photochemie KW - Protonierung KW - RIXS (resonante inelastische Röntgenstreuung) KW - Selektiver Bindungsbruch KW - Stickstoff Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-436688 SN - 1866-8372 IS - 1121 ER - TY - GEN A1 - Couto, Rafael C. A1 - Cruz, Vinicius V. A1 - Ertan, Emelie A1 - Eckert, Sebastian A1 - Fondell, Mattis A1 - Dantz, Marcus A1 - Kennedy, Brian A1 - Schmitt, Thorsten A1 - Pietzsch, Annette A1 - Guimarães, Freddy F. A1 - Ågren, Hans A1 - Gel’mukhanov, Faris A1 - Odelius, Michael A1 - Kimberg, Victor A1 - Föhlisch, Alexander T1 - Selective gating to vibrational modes through resonant X-ray scattering T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1124 KW - potential-energy surface KW - raman-scattering KW - water-vapor KW - spectroscopy KW - chemistry KW - molecule KW - spectrum KW - CM(-1) KW - states KW - NM Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-436926 SN - 1866-8372 IS - 1124 ER - TY - GEN A1 - Eckert, Sebastian A1 - Norell, Jesper A1 - Miedema, Piter S. A1 - Beye, Martin A1 - Fondell, Mattis A1 - Quevedo, Wilson A1 - Kennedy, Brian A1 - Hantschmann, Markus A1 - Pietzsch, Annette A1 - van Kuiken, Benjamin E. A1 - Ross, Matthew A1 - Minitti, Michael P. A1 - Moeller, Stefan P. A1 - Schlotter, William F. A1 - Khalil, Munira A1 - Odelius, Michael A1 - Föhlisch, Alexander T1 - Ultrafast Independent N-H and N-C Bond Deformation Investigated with Resonant Inelastic X-Ray Scattering T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1115 KW - nitrogen KW - photochemistry KW - protonation KW - RIXS (resonant inelastic X-ray scattering) KW - selective bond cleavage Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-436873 SN - 1866-8372 IS - 1115 ER - TY - GEN A1 - Vaz da Cruz, Vinicius A1 - Ertan, Emelie A1 - Couto, Rafael C. A1 - Eckert, Sebastian A1 - Fondell, Mattis A1 - Dantz, Marcus A1 - Kennedy, Brian A1 - Schmitt, Thorsten A1 - Pietzsch, Annette A1 - Guimarães, Freddy F. A1 - Ågren, Hans A1 - Gel'mukhanov, Faris A1 - Odelius, Michael A1 - Föhlisch, Alexander A1 - Kimberg, Victor T1 - A study of the water molecule using frequency control over nuclear dynamics in resonant X-ray scattering T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 781 KW - raman-scattering KW - vibrational structure KW - fast dissociation KW - auger spectrum KW - liquid water KW - spectroscopy KW - emission KW - collapse KW - states KW - vapor Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-436901 SN - 1866-8372 IS - 781 SP - 19573 EP - 19589 ER - TY - GEN A1 - Norell, Jesper A1 - Jay, Raphael Martin A1 - Hantschmann, Markus A1 - Eckert, Sebastian A1 - Guo, Meiyuan A1 - Gaffney, Kelly J. A1 - Wernet, Philippe A1 - Lundberg, Marcus A1 - Föhlisch, Alexander A1 - Odelius, Michael T1 - Fingerprints of electronic, spin and structural dynamics from resonant inelastic soft X-ray scattering in transient photo-chemical species T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 779 KW - charge-transfer KW - relaxation dynamics KW - absorption-spectra KW - energy-conversion KW - basis-sets KW - ab-initio KW - complexes KW - photoelectron KW - spectroscopy KW - simulations Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-437493 SN - 1866-8372 IS - 779 SP - 7243 EP - 7253 ER - TY - GEN A1 - Fondell, Mattis A1 - Eckert, Sebastian A1 - Jay, Raphael Martin A1 - Weniger, Christian A1 - Quevedo, Wilson A1 - Niskanen, Johannes A1 - Kennedy, Brian A1 - Sorgenfrei, Florian A1 - Schick, Daniel A1 - Giangrisostomi, Erika A1 - Ovsyannikov, Ruslan A1 - Adamczyk, Katrin A1 - Huse, Nils A1 - Wernet, Philippe A1 - Mitzner, Rolf A1 - Föhlisch, Alexander T1 - Time-resolved soft X-ray absorption spectroscopy in transmission mode on liquids at MHz repetition rates T2 - Postprints der Universität Potsdam Mathematisch-Naturwissenschaftliche Reihe N2 - We present a setup combining a liquid flatjet sample delivery and a MHz laser system for time-resolved soft X-ray absorption measurements of liquid samples at the high brilliance undulator beamline UE52-SGM at Bessy II yielding unprecedented statistics in this spectral range. We demonstrate that the efficient detection of transient absorption changes in transmission mode enables the identification of photoexcited species in dilute samples. With iron(II)-trisbipyridine in aqueous solution as a benchmark system, we present absorption measurements at various edges in the soft X-ray regime. In combination with the wavelength tunability of the laser system, the set-up opens up opportunities to study the photochemistry of many systems at low concentrations, relevant to materials sciences, chemistry, and biology. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 780 KW - l-edge xas KW - electronic-structure KW - molecular-structure KW - spin-state KW - dynamics KW - complexes KW - probe KW - water KW - iron(II) KW - spectra Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-437529 SN - 1866-8372 IS - 780 ER - TY - GEN A1 - Schick, Daniel A1 - Eckert, Sebastian A1 - Pontius, Niko A1 - Mitzner, Rolf A1 - Föhlisch, Alexander A1 - Holldack, Karsten A1 - Sorgenfrei, Florian T1 - Versatile soft X-ray-optical cross-correlator for ultrafast applications T2 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - We present an X-ray-optical cross-correlator for the soft (> 150 eV) up to the hard X-ray regime based on a molybdenum-silicon superlattice. The cross-correlation is done by probing intensity and position changes of superlattice Bragg peaks caused by photoexcitation of coherent phonons. This approach is applicable for a wide range of X-ray photon energies as well as for a broad range of excitation wavelengths and requires no external fields or changes of temperature. Moreover, the cross-correlator can be employed on a 10 ps or 100 fs time scale featuring up to 50% total X-ray reflectivity and transient signal changes of more than 20%. (C) 2016 Author(s). T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1331 Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-436962 SN - 1866-8372 IS - 1331 SP - 054304-1 EP - 054304-8 ER - TY - JOUR A1 - Vaz da Cruz, Vinicius A1 - Büchner, Robby A1 - Fondell, Mattis A1 - Pietzsch, Annette A1 - Eckert, Sebastian A1 - Föhlisch, Alexander T1 - Targeting individual tautomers in equilibrium by resonant inelastic X-ray scattering JF - The journal of physical chemistry letters N2 - 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. KW - Equilibrium KW - Molecular structure KW - Molecules KW - Nitrogen KW - Solvents Y1 - 2022 U6 - https://doi.org/10.1021/acs.jpclett.1c03453 SN - 1948-7185 VL - 13 IS - 10 SP - 2459 EP - 2466 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Eckert, Sebastian A1 - Beye, Martin A1 - Pietzsch, Annette A1 - Quevedo, Wilson A1 - Hantschmann, Markus A1 - Ochmann, Miguel A1 - Ross, Matthew A1 - Minitti, Michael P. A1 - Turner, Joshua J. A1 - Moeller, Stefan P. A1 - Schlotter, William F. A1 - Dakovski, Georgi L. A1 - Khalil, Munira A1 - Huse, Nils A1 - Föhlisch, Alexander T1 - Principles of femtosecond X-ray/optical cross-correlation with X-ray induced transient optical reflectivity in solids JF - Applied physics letters N2 - 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. Y1 - 2015 U6 - https://doi.org/10.1063/1.4907949 SN - 0003-6951 SN - 1077-3118 VL - 106 IS - 6 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Eckert, Sebastian A1 - Mascarenhas, Eric Johnn A1 - Mitzner, Rolf A1 - Jay, Raphael Martin A1 - Pietzsch, Annette A1 - Fondell, Mattis A1 - Vaz da Cruz, Vinicius A1 - Föhlisch, Alexander T1 - From the free ligand to the transition metal complex BT - FeEDTA(-) formation seen at ligand K-Edges JF - Inorganic chemistry N2 - 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. KW - Energy KW - Ligands KW - Metals KW - Nitrogen KW - Oxygen Y1 - 2022 U6 - https://doi.org/10.1021/acs.inorgchem.2c00789 SN - 0020-1669 SN - 1520-510X VL - 61 IS - 27 SP - 10321 EP - 10328 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Vaz da Cruz, Vinícius A1 - Ignatova, Nina A1 - Couto, Rafael A1 - Fedotov, Daniil A1 - Rehn, Dirk R. A1 - Savchenko, Viktoriia A1 - Norman, Patrick A1 - Ågren, Hans A1 - Polyutov, Sergey A1 - Niskanen, Johannes A1 - Eckert, Sebastian A1 - Jay, Raphael Martin A1 - Fondell, Mattis A1 - Schmitt, Thorsten A1 - Pietzsch, Annette A1 - Föhlisch, Alexander A1 - Odelius, Michael A1 - Kimberg, Victor A1 - Gel’mukhanov, Faris T1 - Nuclear dynamics in resonant inelastic X-ray scattering and X-ray absorption of methanol JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - 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). Y1 - 2019 U6 - https://doi.org/10.1063/1.5092174 SN - 0021-9606 SN - 1089-7690 VL - 150 IS - 23 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Schreck, Simon A1 - Beye, Martin A1 - Sellberg, Jonas A. A1 - McQueen, Trevor A1 - Laksmono, Hartawan A1 - Kennedy, Brian A1 - Eckert, Sebastian A1 - Schlesinger, Daniel A1 - Nordlund, Dennis A1 - Ogasawara, Hirohito A1 - Sierra, Raymond G. A1 - Segtnan, Vegard H. A1 - Kubicek, Katharina A1 - Schlotter, William F. A1 - Dakovski, Georgi L. A1 - Moeller, Stefan P. A1 - Bergmann, Uwe A1 - Techert, Simone A1 - Pettersson, Lars G. M. A1 - Wernet, Philippe A1 - Bogan, Michael J. A1 - Harada, Yoshihisa A1 - Nilsson, Anders A1 - Föhlisch, Alexander T1 - Reabsorption of soft x-ray emission at high x-ray free-electron laserfluences JF - Physical review letters N2 - 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. Y1 - 2014 U6 - https://doi.org/10.1103/PhysRevLett.113.153002 SN - 0031-9007 SN - 1079-7114 VL - 113 IS - 15 PB - American Physical Society CY - College Park ER - TY - JOUR A1 - Ochmann, Miguel A1 - Vaz da Cruz, Vinicius A1 - Eckert, Sebastian A1 - Huse, Nils A1 - Föhlisch, Alexander T1 - R-Group stabilization in methylated formamides observed by resonant inelastic X-ray scattering JF - Chemical communications: ChemComm N2 - 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. Y1 - 2022 U6 - https://doi.org/10.1039/d2cc00053a SN - 1359-7345 SN - 1364-548X VL - 58 IS - 63 SP - 8834 EP - 8837 PB - The Royal Society of Chemistry CY - Cambridge ER - TY - GEN A1 - Niskanen, Johannes A1 - Fondell, Mattis A1 - Sahle, Christoph J. A1 - Eckert, Sebastian A1 - Jay, Raphael Martin A1 - Gilmore, Keith A1 - Pietzsch, Annette A1 - Dantz, Marcus A1 - Lu, Xingye A1 - McNally, Daniel E. A1 - Schmitt, Thorsten A1 - Vaz da Cruz, Vinicius A1 - Kimberg, Victor A1 - Föhlisch, Alexander T1 - Reply to Pettersson et al.: Why X-ray spectral features are compatible to continuous distribution models in ambient water T2 - Proceedings of the National Academy of Sciences of the United States of America Y1 - 2019 U6 - https://doi.org/10.1073/pnas.1909551116 SN - 0027-8424 VL - 116 IS - 35 SP - 17158 EP - 17159 PB - National Acad. of Sciences CY - Washington ER - TY - GEN A1 - Eckert, Sebastian A1 - Miedema, Piter A1 - Quevedo, Wilson A1 - O'Cinneide, B. A1 - Fondell, Mattis A1 - Beye, Martin A1 - Pietzsch, Annette A1 - Ross, Matthew R. A1 - Khalil, Munira A1 - Föhlisch, Alexander T1 - Molecular structures and protonation state of 2-Mercaptopyridine in aqueous solution T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - 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. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 953 KW - ray-emission-spectroscopy KW - x-ray KW - hydroxypyridine-pyridone KW - protomeric equilibria KW - self-association KW - CU(110) KW - valence Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-437473 SN - 1866-8372 IS - 953 SP - 103 EP - 106 ER - TY - JOUR A1 - Sellberg, Jonas A. A1 - McQueen, Trevor A. A1 - Laksmono, Hartawan A1 - Schreck, Simon A1 - Beye, Martin A1 - DePonte, Daniel P. A1 - Kennedy, Brian A1 - Nordlund, Dennis A1 - Sierra, Raymond G. A1 - Schlesinger, Daniel A1 - Tokushima, Takashi A1 - Zhovtobriukh, Iurii A1 - Eckert, Sebastian A1 - Segtnan, Vegard H. A1 - Ogasawara, Hirohito A1 - Kubicek, Katharina A1 - Techert, Simone A1 - Bergmann, Uwe A1 - Dakovski, Georgi L. A1 - Schlotter, William F. A1 - Harada, Yoshihisa A1 - Bogan, Michael J. A1 - Wernet, Philippe A1 - Föhlisch, Alexander A1 - Pettersson, Lars G. M. A1 - Nilsson, Anders T1 - X-ray emission spectroscopy of bulk liquid water in "no-man's land" JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - 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. Y1 - 2015 U6 - https://doi.org/10.1063/1.4905603 SN - 0021-9606 SN - 1089-7690 VL - 142 IS - 4 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Kunnus, Kristjan A1 - Rajkovic, Ivan A1 - Schreck, Simon A1 - Quevedo, Wilson A1 - Eckert, Sebastian A1 - Beye, Martin A1 - Suljoti, Edlira A1 - Weniger, Christian A1 - Kalus, Christian A1 - Gruebel, Sebastian A1 - Scholz, Mirko A1 - Nordlund, Dennis A1 - Zhang, Wenkai A1 - Hartsock, Robert W. A1 - Gaffney, Kelly J. A1 - Schlotter, William F. A1 - Turner, Joshua J. A1 - Kennedy, Brian A1 - Hennies, Franz A1 - Techert, Simone A1 - Wernet, Philippe A1 - Föhlisch, Alexander T1 - A setup for resonant inelastic soft x-ray scattering on liquids at free electron laser light sources JF - Review of scientific instruments : a monthly journal devoted to scientific instruments, apparatus, and techniques N2 - 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. Y1 - 2012 U6 - https://doi.org/10.1063/1.4772685 SN - 0034-6748 VL - 83 IS - 12 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Fondell, Mattis A1 - Eckert, Sebastian A1 - Jay, Raphael Martin A1 - Weniger, Christian A1 - Quevedo, Wilson A1 - Niskanen, Johannes A1 - Kennedy, Brian A1 - Sorgenfrei, Florian A1 - Schick, Daniel A1 - Giangrisostomi, Erika A1 - Ovsyannikov, Ruslan A1 - Adamczyk, Katrin A1 - Huse, Nils A1 - Wernet, Philippe A1 - Mitzner, Rolf A1 - Föhlisch, Alexander T1 - Time-resolved soft X-ray absorption spectroscopy in transmission mode on liquids at MHz repetition rates JF - Structural dynamics N2 - We present a setup combining a liquid flatjet sample delivery and a MHz laser system for time-resolved soft X-ray absorption measurements of liquid samples at the high brilliance undulator beamline UE52-SGM at Bessy II yielding unprecedented statistics in this spectral range. We demonstrate that the efficient detection of transient absorption changes in transmission mode enables the identification of photoexcited species in dilute samples. With iron(II)-trisbipyridine in aqueous solution as a benchmark system, we present absorption measurements at various edges in the soft X-ray regime. In combination with the wavelength tunability of the laser system, the set-up opens up opportunities to study the photochemistry of many systems at low concentrations, relevant to materials sciences, chemistry, and biology. (C) 2017 Author(s). Y1 - 2017 U6 - https://doi.org/10.1063/1.4993755 SN - 2329-7778 VL - 4 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Eckert, Sebastian A1 - Norell, Jesper A1 - Miedema, Piter S. A1 - Beye, Martin A1 - Fondell, Mattis A1 - Quevedo, Wilson A1 - Kennedy, Brian A1 - Hantschmann, Markus A1 - Pietzsch, Annette A1 - van Kuiken, Benjamin A1 - Ross, Matthew A1 - Minitti, Michael P. A1 - Moeller, Stefan P. A1 - Schlotter, William F. A1 - Khalil, Munira A1 - Odelius, Michael A1 - Föhlisch, Alexander T1 - Untersuchung unabhängiger N‐H‐ und N‐C‐Bindungsverformungen auf ultrakurzen Zeitskalen mit resonanter inelastischer Röntgenstreuung JF - Angewandte Chemie N2 - Die Femtosekundendynamik nach resonanten Photoanregungen mit optischen und Röntgenpulsen ermöglicht eine selektive Verformung von chemischen N‐H‐ und N‐C‐Bindungen in 2‐Thiopyridon in wässriger Lösung. Die Untersuchung der orbitalspezifischen elektronischen Struktur und ihrer Dynamik auf ultrakurzen Zeitskalen mit resonanter inelastischer Röntgenstreuung an der N1s‐Resonanz am Synchrotron und dem Freie‐Elektronen‐Laser LCLS in Kombination mit quantenchemischen Multikonfigurationsberechnungen erbringen den direkten Nachweis dieser kontrollierten photoinduzierten Molekülverformungen und ihrer ultrakurzen Zeitskala. KW - Photochemie KW - Protonierung KW - RIXS (resonante inelastische Röntgenstreuung) KW - Selektiver Bindungsbruch KW - Stickstoff Y1 - 2017 U6 - https://doi.org/10.1002/ange.201700239 SN - 1521-3757 SN - 1521-3773 VL - 129 IS - 22 SP - 6184 EP - 6188 ER - TY - JOUR A1 - Eckert, Sebastian A1 - Norell, Jesper A1 - Miedema, Piter S. A1 - Beye, Martin A1 - Fondell, Mattis A1 - Quevedo, Wilson A1 - Kennedy, Brian A1 - Hantschmann, Markus A1 - Pietzsch, Annette A1 - Van Kuiken, Benjamin E. A1 - Ross, Matthew A1 - Minitti, Michael P. A1 - Moeller, Stefan P. A1 - Schlotter, William F. A1 - Khalil, Munira A1 - Odelius, Michael A1 - Föhlisch, Alexander T1 - Ultrafast Independent N-H and N-C Bond Deformation Investigated with Resonant Inelastic X-Ray Scattering JF - Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition N2 - 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. KW - nitrogen KW - photochemistry KW - protonation KW - RIXS (resonant inelastic X-ray scattering) KW - selective bond cleavage Y1 - 2017 U6 - https://doi.org/10.1002/anie.201700239 SN - 1433-7851 SN - 1521-3773 VL - 56 SP - 6088 EP - 6092 PB - Wiley-VCH CY - Weinheim ER - TY - JOUR A1 - Vaz da Cruz, Vinicius A1 - Ertan, Emelie A1 - Couto, Rafael C. A1 - Eckert, Sebastian A1 - Fondell, Mattis A1 - Dantz, Marcus A1 - Kennedy, Brian A1 - Schmitt, Thorsten A1 - Pietzsch, Annette A1 - Guimaraes, Freddy F. A1 - Ågren, Hans A1 - Odelius, Michael A1 - Föhlisch, Alexander A1 - Kimberg, Victor T1 - A study of the water molecule using frequency control over nuclear dynamics in resonant X-ray scattering JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - 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. Y1 - 2017 U6 - https://doi.org/10.1039/c7cp01215b SN - 1463-9076 SN - 1463-9084 VL - 19 SP - 19573 EP - 19589 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Norell, Jesper A1 - Eckert, Sebastian A1 - Van Kuiken, Benjamin E. A1 - Föhlisch, Alexander A1 - Odelius, Michael T1 - Ab initio simulations of complementary K-edges and solvatization effects for detection of proton transfer in aqueous 2-thiopyridone JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - 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. Y1 - 2019 U6 - https://doi.org/10.1063/1.5109840 SN - 0021-9606 SN - 1089-7690 VL - 151 IS - 11 PB - American Institute of Physics CY - Melville ER -