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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - 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 - Guimaraes, Freddy F. A1 - Agren, Hans A1 - Odelius, Michael A1 - Kimberg, Victor A1 - Föhlisch, Alexander T1 - Selective gating to vibrational modes through resonant X-ray scattering JF - Nature Communications 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. Y1 - 2017 U6 - https://doi.org/10.1038/ncomms14165 SN - 2041-1723 VL - 8 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Eckert, Sebastian A1 - Vaz da Cruz, Vinicius A1 - Ertan, Emelie A1 - Ignatova, Nina A1 - Polyutov, Sergey A1 - Couto, Rafael C. A1 - Fondell, Mattis A1 - Dantz, Marcus A1 - Kennedy, Brian A1 - Schmitt, Thorsten A1 - Pietzsch, Annette A1 - Odelius, Michael A1 - Föhlisch, Alexander T1 - One-dimensional cuts through multidimensional potential-energy surfaces by tunable x rays JF - Physical review : A, Atomic, molecular, and optical physics N2 - The concept of the potential-energy surface (PES) and directional reaction coordinates is the backbone of our description of chemical reaction mechanisms. Although the eigenenergies of the nuclear Hamiltonian uniquely link a PES to its spectrum, this information is in general experimentally inaccessible in large polyatomic systems. This is due to (near) degenerate rovibrational levels across the parameter space of all degrees of freedom, which effectively forms a pseudospectrum given by the centers of gravity of groups of close-lying vibrational levels. We show here that resonant inelastic x-ray scattering (RIXS) constitutes an ideal probe for revealing one-dimensional cuts through the ground-state PES of molecular systems, even far away from the equilibrium geometry, where the independent-mode picture is broken. We strictly link the center of gravity of close-lying vibrational peaks in RIXS to a pseudospectrum which is shown to coincide with the eigenvalues of an effective one-dimensional Hamiltonian along the propagation coordinate of the core-excited wave packet. This concept, combined with directional and site selectivity of the core-excited states, allows us to experimentally extract cuts through the ground-state PES along three complementary directions for the showcase H2O molecule. Y1 - 2018 U6 - https://doi.org/10.1103/PhysRevA.97.053410 SN - 2469-9926 SN - 2469-9934 VL - 97 IS - 5 PB - American Physical Society CY - College Park ER -