TY - JOUR A1 - Sahle, Christoph J. A1 - Niskanen, Johannes A1 - Schmidt, Christian A1 - Stefanski, Johannes A1 - Gilmore, Keith A1 - Forov, Yury A1 - Jahn, Sandro A1 - Wilke, Max A1 - Sternemann, Christian T1 - Cation Hydration in Supercritical NaOH and HCl Aqueous Solutions JF - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry N2 - We present a study of the local atomic environment of the oxygen atoms in the aqueous solutions of NaOH and HCl under simultaneous high-temperature and high-pressure conditions. Experimental nonresonant X-ray Raman scattering core-level spectra at the oxygen K-edge show systematic changes as a function of temperature and pressure. These systematic changes are distinct for the two different solutes and are described well by calculations within the Bethe- Salpeter formalism for snapshots from ab initio molecular dynamics simulations. The agreement between experimental and simulation results allows us to use the computations for a detailed fingerprinting analysis in an effort to elucidate the local atomic structure and hydrogen-bonding topology in these relevant solutions. We observe that both electrolytes, especially NaOH, enhance hydrogen bonding and tetrahedrality in the water structure at supercritical conditions, in particular in the vicinity of the hydration shells. This effect is accompanied with the association of the HCl and NaOH molecules at elevated temperatures. Y1 - 2017 U6 - https://doi.org/10.1021/acs.jpcb.7b09688 SN - 1520-6106 VL - 121 SP - 11383 EP - 11389 PB - American Chemical Society CY - Washington 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 - 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 - Eckert, Sebastian A1 - Niskanen, Johannes A1 - Jay, Raphael Martin A1 - Miedema, Piter S. A1 - Fondell, Mattis A1 - Kennedy, Brian A1 - Quevedo, Wilson A1 - Iannuzzi, Marcella A1 - Föhlisch, Alexander T1 - Valence orbitals and local bond dynamics around N atoms of histidine under X-ray irradiation JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - The valence orbitals of aqueous histidine under basic, neutral and acidic conditions and their X-ray induced transformations have been monitored through N 1s resonant inelastic X-ray scattering. Using density functional ab initio molecular dynamics simulations in the core-hole state within the Z + 1 approximation, core-excitation-induced molecular transformations are quantified. Spectroscopic evidence for a highly directional X-ray-induced local N-H dissociation within the scattering duration is presented for acidic histidine. Our report demonstrates a protonation-state and chemical-environment dependent propensity for a molecular dissociation, which is induced by the absorption of high energy photons. This case study indicates that structural deformations in biomolecules under exposure to ionizing radiation, yielding possible alteration or loss of function, is highly dependent on the physiological state of the molecule upon irradiation. Y1 - 2017 U6 - https://doi.org/10.1039/c7cp05713j SN - 1463-9076 SN - 1463-9084 VL - 19 SP - 32091 EP - 32098 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR 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 A1 - Gel’mukhanov, Faris T1 - Compatibility of quantitative X-ray spectroscopy with continuous distribution models of water at ambient conditions JF - Proceedings of the National Academy of Sciences of the United States of America N2 - The phase diagram of water harbors controversial views on underlying structural properties of its constituting molecular moieties, its fluctuating hydrogen-bonding network, as well as pair-correlation functions. In this work, long energy-range detection of the X-ray absorption allows us to unambiguously calibrate the spectra for water gas, liquid, and ice by the experimental atomic ionization cross-section. In liquid water, we extract the mean value of 1.74 +/- 2.1% donated and accepted hydrogen bonds per molecule, pointing to a continuous-distribution model. In addition, resonant inelastic X-ray scattering with unprecedented energy resolution also supports continuous distribution of molecular neighborhoods within liquid water, as do X-ray emission spectra once the femtosecond scattering duration and proton dynamics in resonant X-ray-matter interaction are taken into account. Thus, X-ray spectra of liquid water in ambient conditions can be understood without a two-structure model, whereas the occurrence of nanoscale-length correlations within the continuous distribution remains open. KW - structure of water KW - X-ray spectroscopy KW - continuous distribution model Y1 - 2019 U6 - https://doi.org/10.1073/pnas.1815701116 SN - 0027-8424 VL - 116 IS - 10 SP - 4058 EP - 4063 PB - National Acad. of Sciences CY - Washington ER - TY - JOUR A1 - Vaz da Cruz, Vinicius A1 - Eckert, Sebastian A1 - Iannuzzi, Marcella A1 - Ertan, Emelie A1 - Pietzsch, Annette A1 - Couto, Rafael C. A1 - Niskanen, Johannes A1 - Fondell, Mattis A1 - Dantz, Marcus A1 - Schmitt, Thorsten A1 - Lu, Xingye A1 - McNally, Daniel A1 - Jay, Raphael Martin A1 - Kimberg, Victor A1 - Föhlisch, Alexander A1 - Odelius, Michael T1 - Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering JF - Nature Communications N2 - Local probes of the electronic ground state are essential for understanding hydrogen bonding in aqueous environments. When tuned to the dissociative core-excited state at the O1s pre-edge of water, resonant inelastic X-ray scattering back to the electronic ground state exhibits a long vibrational progression due to ultrafast nuclear dynamics. We show how the coherent evolution of the OH bonds around the core-excited oxygen provides access to high vibrational levels in liquid water. The OH bonds stretch into the long-range part of the potential energy curve, which makes the X-ray probe more sensitive than infra-red spectroscopy to the local environment. We exploit this property to effectively probe hydrogen bond strength via the distribution of intramolecular OH potentials derived from measurements. In contrast, the dynamical splitting in the spectral feature of the lowest valence-excited state arises from the short-range part of the OH potential curve and is rather insensitive to hydrogen bonding. Y1 - 2019 U6 - https://doi.org/10.1038/s41467-019-08979-4 SN - 2041-1723 VL - 10 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Jay, Raphael Martin A1 - Eckert, Sebastian A1 - Fondell, Mattis A1 - Miedema, Piter S. A1 - Norell, Jesper A1 - Pietzsch, Annette A1 - Quevedo, Wilson A1 - Niskanen, Johannes A1 - Kunnus, Kristjan A1 - Föhlisch, Alexander T1 - The nature of frontier orbitals under systematic ligand exchange in (pseudo-)octahedral Fe(II) complexes JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Understanding and controlling properties of transition metal complexes is a crucial step towards tailoring materials for sustainable energy applications. In a systematic approach, we use resonant inelastic X-ray scattering to study the influence of ligand substitution on the valence electronic structure around an aqueous iron(II) center. Exchanging cyanide with 2-2′-bipyridine ligands reshapes frontier orbitals in a way that reduces metal 3d charge delocalization onto the ligands. This net decrease of metal–ligand covalency results in lower metal-centered excited state energies in agreement with previously reported excited state dynamics. Furthermore, traces of solvent-effects were found indicating a varying interaction strength of the solvent with ligands of different character. Our results demonstrate how ligand exchange can be exploited to shape frontier orbitals of transition metal complexes in solution-phase chemistry; insights upon which future efforts can built when tailoring the functionality of photoactive systems for light-harvesting applications. Y1 - 2018 U6 - https://doi.org/10.1039/c8cp04341h SN - 1463-9076 SN - 1463-9084 VL - 20 IS - 44 SP - 27745 EP - 27751 PB - Royal Society of Chemistry CY - Cambridge ER - TY - JOUR A1 - Pietzsch, Annette A1 - Niskanen, Johannes A1 - Vaz da Cruz, Vinicius A1 - Büchner, Robby A1 - Eckert, Sebastian A1 - Fondell, Mattis A1 - Jay, Raphael Martin A1 - Lu, Xingye A1 - McNally, Daniel A1 - Schmitt, Thorsten A1 - Föhlisch, Alexander T1 - Cuts through the manifold of molecular H2O potential energy surfaces in liquid water at ambient conditions JF - Proceedings of the National Academy of Sciences of the United States of America N2 - The fluctuating hydrogen bridge bonded network of liquid water at ambient conditions entails a varied ensemble of the underlying constituting H2O molecular moieties. This is mirrored in a manifold of the H2O molecular potentials. Subnatural line width resonant inelastic X-ray scattering allowed us to quantify the manifold of molecular potential energy surfaces along the H2O symmetric normal mode and the local asymmetric O-H bond coordinate up to 1 and 1.5 angstrom, respectively. The comparison of the single H2O molecular potentials and spectroscopic signatures with the ambient conditions liquid phase H2O molecular potentials is done on various levels. In the gas phase, first principles, Morse potentials, and stepwise harmonic potential reconstruction have been employed and benchmarked. In the liquid phase the determination of the potential energy manifold along the local asymmetric O-H bond coordinate from resonant inelastic X-ray scattering via the bound state oxygen ls to 4a(1) resonance is treated within these frameworks. The potential energy surface manifold along the symmetric stretch from resonant inelastic X-ray scattering via the oxygen 1 s to 2b(2) resonance is based on stepwise harmonic reconstruction. We find in liquid water at ambient conditions H2O molecular potentials ranging from the weak interaction limit to strongly distorted potentials which are put into perspective to established parameters, i.e., intermolecular O-H, H-H, and O-O correlation lengths from neutron scattering. KW - water KW - potential ene rgy surface KW - RIXS Y1 - 2022 U6 - https://doi.org/10.1073/pnas.2118101119 SN - 1091-6490 VL - 119 IS - 28 PB - National Acad. of Sciences CY - Washington, DC 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 - 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 - 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 - 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 -