| 1. |
- Born, Artur, et al.
(author)
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Quantification of Ni L-2,L-3 core-hole relaxation pathways utilizing Auger photoelectron coincidence spectroscopy
- 2021
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In: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:11
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Journal article (peer-reviewed)abstract
- Ni LVV Auger spectra, in coincidence with the corresponding 2p(1/2), 2p(3/2), and 6 eV satellite photoelectrons, have been used to examine electron correlation and itinerance effects in Ni. In coincidence with the 2p(3/2) core level, the Auger spectral shape is represented by localized 3d(8) and itinerant valence final states with an additional 3d(7) Auger shake-up contribution. The spectra in coincidence with the 6 eV satellite probe the decay of localized 2p(5)3d(9) double hole states, leading to 3d(7) final states. It is found that a fraction of the double hole states delocalize before the Auger decay. A similar delocalization is observed for the double hole states produced by the L2L3M45 Coster-Kronig process, and the delocalization rates have been determined.
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| 2. |
- C. Couto, Rafael, 1987-, et al.
(author)
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Selective gating to vibrational modes through resonant X-ray scattering
- 2017
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In: Nature Communications. - : Macmillan Publishers Ltd.. - 2041-1723. ; 8, s. 14165-1-14165-7
-
Journal article (peer-reviewed)abstract
- The dynamics of fragmentation and vibration of molecular systems with a large number of coupled degrees of freedom are key aspects for understanding chemical reactivity and properties. Here we present a resonant inelastic X-ray scattering (RIXS) study to show how it is possible to break down such a complex multidimensional problem into elementary components. Local multimode nuclear wave packets created by X-ray excitation to different core-excited potential energy surfaces (PESs) will act as spatial gates to selectively probe the particular ground-state vibrational modes and, hence, the PES along these modes. We demonstrate this principle by combining ultra-high resolution RIXS measurements for gas-phase water with state-of-the-art simulations.
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| 3. |
- Cappel, Ute B, et al.
(author)
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Partially Reversible Photoinduced Chemical Changes in a Mixed-Ion Perovskite Material for Solar Cells.
- 2017
-
In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 9:40, s. 34970-34978
-
Journal article (peer-reviewed)abstract
- ) 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.
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| 4. |
- da Cruz, Vinicius Vaz, et al.
(author)
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Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering
- 2019
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In: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10
-
Journal article (peer-reviewed)abstract
- Local probes of the electronic ground state are essential for understanding hydrogen bonding in aqueous environments. When tuned to the dissociative core-excited state at the O1s pre-edge of water, resonant inelastic X-ray scattering back to the electronic ground state exhibits a long vibrational progression due to ultrafast nuclear dynamics. We show how the coherent evolution of the OH bonds around the core-excited oxygen provides access to high vibrational levels in liquid water. The OH bonds stretch into the long-range part of the potential energy curve, which makes the X-ray probe more sensitive than infra-red spectroscopy to the local environment. We exploit this property to effectively probe hydrogen bond strength via the distribution of intramolecular OH potentials derived from measurements. In contrast, the dynamical splitting in the spectral feature of the lowest valence-excited state arises from the short-range part of the OH potential curve and is rather insensitive to hydrogen bonding.
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| 5. |
- Eckert, Sebastian, et al.
(author)
-
From the Free Ligand to the Transition Metal Complex : FeEDTA- Formation Seen at Ligand K-Edges
- 2022
-
In: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 61:27, s. 10321-10328
-
Journal article (peer-reviewed)abstract
- Chelating agents are an integral part of transition metal complex chemistry with broad biological and industrial relevance. The hexadentate chelating agent ethylenediaminetetraacetic acid (EDTA) has the capability to bind to metal ions at its two nitrogen and four of its carboxylate oxygen sites. We use resonant inelastic X-ray scattering at the 1s absorption edge of the aforementioned elements in EDTA and the iron(III)-EDTA complex to investigate the impact of the metal-ligand bond formation on the electronic structure of EDTA. Frontier orbital distortions, occupation changes, and energy shifts through metal- ligand bond formation are probed through distinct spectroscopic signatures.
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| 6. |
- Eckert, Sebastian, et al.
(author)
-
One-dimensional cuts through multidimensional potential-energy surfaces by tunable x rays
- 2018
-
In: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : AMER PHYSICAL SOC. - 2469-9926 .- 2469-9934. ; 97:5
-
Journal article (peer-reviewed)abstract
- The concept of the potential-energy surface (PES) and directional reaction coordinates is the backbone of our description of chemical reaction mechanisms. Although the eigenenergies of the nuclear Hamiltonian uniquely link a PES to its spectrum, this information is in general experimentally inaccessible in large polyatomic systems. This is due to (near) degenerate rovibrational levels across the parameter space of all degrees of freedom, which effectively forms a pseudospectrum given by the centers of gravity of groups of close-lying vibrational levels. We show here that resonant inelastic x-ray scattering (RIXS) constitutes an ideal probe for revealing one-dimensional cuts through the ground-state PES of molecular systems, even far away from the equilibrium geometry, where the independent-mode picture is broken. We strictly link the center of gravity of close-lying vibrational peaks in RIXS to a pseudospectrum which is shown to coincide with the eigenvalues of an effective one-dimensional Hamiltonian along the propagation coordinate of the core-excited wave packet. This concept, combined with directional and site selectivity of the core-excited states, allows us to experimentally extract cuts through the ground-state PES along three complementary directions for the showcase H2O molecule.
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| 7. |
- Eckert, Sebastian, et al.
(author)
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T-1 Population as the Driver of Excited-State Proton-Transfer in 2-Thiopyridone
- 2019
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In: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 25:7, s. 1733-1739
-
Journal article (peer-reviewed)abstract
- Excited-state proton transfer (ESPT) is a fundamental process in biomolecular photochemistry, but its underlying mediators often evade direct observation. We identify a distinct pathway for ESPT in aqueous 2-thiopyridone, by employing transient N1s X-ray absorption spectroscopy and multi-configurational spectrum simulations. Photoexcitations to the singlet S-2 and S-4 states both relax promptly through intersystem crossing to the triplet T-1 state. The T-1 state, through its rapid population and near nanosecond lifetime, mediates nitrogen site deprotonation by ESPT in a secondary intersystem crossing to the S-0 potential energy surface. This conclusively establishes a dominant ESPT pathway for the system in aqueous solution, which is also compatible with previous measurements in acetonitrile. Thereby, the hitherto open questions of the pathway for ESPT in the compound, including its possible dependence on excitation wavelength and choice of solvent, are resolved.
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| 8. |
- Eckert, Sebastian, et al.
(author)
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Ultrafast Independent N-H and N-C Bond Deformation Investigated with Resonant Inelastic X-Ray Scattering
- 2017
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In: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 56:22, s. 6088-6092
-
Journal article (peer-reviewed)abstract
- The femtosecond excited-state dynamics following resonant photoexcitation enable the selective deformation of N-H and N-C chemical bonds in 2-thiopyridone in aqueous solution with optical or X-ray pulses. In combination with multiconfigurational quantum-chemical calculations, the orbital-specific electronic structure and its ultrafast dynamics accessed with resonant inelastic X-ray scattering at the N 1s level using synchrotron radiation and the soft X-ray free-electron laser LCLS provide direct evidence for this controlled photoinduced molecular deformation and its ultrashort time-scale.
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| 9. |
- Ertan, Emelie, et al.
(author)
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Ultrafast dissociation features in RIXS spectra of the water molecule
- 2018
-
In: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076 .- 1463-9084.
-
Journal article (peer-reviewed)abstract
- In this combined theoretical and experimental study we report on an analysis of the resonant inelastic X-ray scattering spectra (RIXS) of gas phase water via the lowest dissociative core-excited state |1sO-14a11〉. We focus on the spectral feature near the dissociation limit of the electronic ground state. We show that the narrow atomic-like peak consists of the overlapping contribution from the RIXS channels back to the ground state and to the first valence excited state |1b1-14a11〉 of the molecule. The spectral feature has signatures of ultrafast dissociation (UFD) in the core-excited state, as we show by means of ab initio calculations and time-dependent nuclear wave packet simulations. We show that the electronically elastic RIXS channel gives substantial contribution to the atomic-like resonance due to the strong bond length dependence of the magnitude and orientation of the transition dipole moment. By studying the RIXS for an excitation energy scan over the core-excited state resonance, we can understand and single out the molecular and atomic-like contributions in the decay to the lowest valence-excited state. Our study is complemented by a theoretical discussion of RIXS in the case of the isotope substituted water (HDO and D2O) where the nuclear dynamics is significantly affected by the heavier fragments' mass.
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| 10. |
- Ertan, Emelie, et al.
(author)
-
Ultrafast dissociation features in RIXS spectra of the water molecule
-
Other publication (other academic/artistic)abstract
- In this combined theoretical and experimental study we report on an analysis of the resonant inelastic X-ray scattering spectra (RIXS) of gas phase water via the lowest dissociative core-excited state |1sO-14a11>. We focus on the spectral feature near the dissociation limit of the electronic ground state. We show that the narrow atomic-like peak consists of the overlapping contribution from the RIXS channels back to the ground state and to the first valence excited state |1b1-14a11> of the molecule. The spectral feature has signatures of ultrafast dissociation (UFD) in the core-excited state, as we show by means of ab initio calculations and time-dependent nuclear wave packet simulations. We show that the electronically elastic RIXS channel gives substantial contribution to the atomic-like resonance due to the strong bond length dependence of the magnitude and orientation of the transition dipole moment. By studying the RIXS for an excitation energy scan over the core-excited state resonance, we can understand and single out the molecular and atomic-like contributions in the decay to the lowest valence-excited state. Our study is complemented by a theoretical discussion of RIXS in the case of the isotope substituted water (HDO and D2O) where the nuclear dynamics is significantly affected by the heavier fragments' mass.
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| 11. |
- Föhlisch, Alexander
(author)
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Probing molecular adsorbates with core level spectroscopies : Electronic structure and bonding models
- 1999
-
Doctoral thesis (other academic/artistic)abstract
- Resonantly excited X-ray emission spectroscopy has been applied to study the valence electronic structure of molecular adsorbates in an atom specific and orbital symmetry selective manner. In combination with ab initio cluster calculations, electronic structure and bonding models have been derived. Existing models of surface chemical bonding have been reviewed and partially revised.Most notably, the bonding mechanism of carbon monoxide (CO) on transition and noble metals has been revised and is found to be the result of a strong covalent interaction between the CO orbitals and the metal bands within each orbital symmetry. A characteristic allylic configuration is found in the π-system and strong polarization within the (Σ system. The equilibrium properties of adsorbed CO are the direct result of a balance between the repulsive Σ-interaction and the attractive π-interaction; both in terms of the total energy and the local bond properties. The bonding of ammonia (NH3) on the Cu(ll0) surface is found to be dominated by a large covalent interaction, which contrasts the previous model of a strong electrostatic interaction. Furthermore, adsorbate-adsorbate interaction leads to a tilted adsorption geometry. Ethylene (C2H4) on Cu(ll0) is adsorbed in the di-Σ configuration, according to the generally accepted Dewar Chatt Duncanson model for hydrocarbon adsorption. The application and interpretation of resonantly excited X-ray emission on these systems also required a thorough discussion of the spectroscopic process.Another topic was the vibrational fine structure in the X-ray photoemission corelevel main lines of adsorbed molecules. The observation of the vibrational fine structure in molecular adsorbates is remarkable, as it was previously thought impossible to observe due to solid state broadening contributions. A detailed analysis of the vibrational fine structure and the line profile makes it possible to study the electronic and geometric properties of the core-ionized adsorbate and the dynamic response to core-ionization in unprecedented detail. A connection between the vibrational fine structure and the local chemical environment has been found. Furthermore, our basic understanding of the photoemission process on adsorbates is put to the test in the photon energy dependence of the vibrational fine structure.
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| 12. |
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| 13. |
- Hennies, Franz, et al.
(author)
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Resonant Inelastic Scattering Spectra of Free Molecules with Vibrational Resolution
- 2010
-
In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:19, s. 193002-
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Journal article (peer-reviewed)abstract
- Inelastic x-ray scattering spectra excited at the 1s(-1) pi* resonance of gas phase O-2 have been recorded with an overall energy resolution that allows for well-resolved vibrational progressions. The nuclear wave packet dynamics in the intermediate state is reflected in vibrational excitations of the electronic ground state, and by fine-tuning the excitation energy the dissociation dynamics in the predissociative B' (3) Pi(g) final state is controlled.
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| 14. |
- Higley, Daniel J., et al.
(author)
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Stimulated resonant inelastic X-ray scattering in a solid
- 2022
-
In: Communications Physics. - : Springer Science and Business Media LLC. - 2399-3650. ; 5
-
Journal article (peer-reviewed)abstract
- When materials are exposed to X-ray pulses with sufficiently high intensity, various nonlinear effects can occur. The most fundamental one consists of stimulated electronic decays after resonant absorption of X-rays. Such stimulated decays enhance the number of emitted photons and the emission direction is confined to that of the stimulating incident photons which clone themselves in the process. Here we report the observation of stimulated resonant elastic (REXS) and inelastic (RIXS) X-ray scattering near the cobalt L3 edge in solid Co/Pd multilayer samples. We observe an enhancement of order 106 of the stimulated over the conventional spontaneous RIXS signal into the small acceptance angle of the RIXS spectrometer. We also find that in solids both stimulated REXS and RIXS spectra contain contributions from inelastic electron scattering processes, even for ultrashort 5 fs pulses. Our results reveal the potential and caveats of the development of stimulated RIXS in condensed matter.
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| 15. |
- Jay, Raphael M., et al.
(author)
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Disentangling Transient Charge Density and Metal-Ligand Covalency in Photoexcited Ferricyanide with Femtosecond Resonant Inelastic Soft X-ray Scattering
- 2018
-
In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 9:12, s. 3538-3543
-
Journal article (peer-reviewed)abstract
- Soft X-ray spectroscopies are ideal probes of the local valence electronic structure of photocatalytically active metal sites. Here, we apply the selectivity of time resolved resonant inelastic X-ray scattering at the iron L-edge to the transient charge distribution of an optically excited charge-transfer state in aqueous ferricyanide. Through comparison to steady-state spectra and quantum chemical calculations, the coupled effects of valence-shell closing and ligand-hole creation are experimentally and theoretically disentangled and described in terms of orbital occupancy, metal-ligand covalency, and ligand field splitting, thereby extending established steady-state concepts to the excited-state domain. pi-Back-donation is found to be mainly determined by the metal site occupation, whereas the ligand hole instead influences sigma-donation. Our results demonstrate how ultrafast resonant inelastic X-ray scattering can help characterize local charge distributions around catalytic metal centers in short-lived charge-transfer excited states, as a step toward future rationalization and tailoring of photocatalytic capabilities of transition-metal complexes.
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| 16. |
- Jay, Raphael M., et al.
(author)
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The nature of frontier orbitals under systematic ligand exchange in (pseudo-)octahedral Fe(II) complexes
- 2018
-
In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 20:44, s. 27745-27751
-
Journal article (peer-reviewed)abstract
- Understanding and controlling properties of transition metal complexes is a crucial step towards tailoring materials for sustainable energy applications. In a systematic approach, we use resonant inelastic X-ray scattering to study the influence of ligand substitution on the valence electronic structure around an aqueous iron(II) center. Exchanging cyanide with 2-2'-bipyridine ligands reshapes frontier orbitals in a way that reduces metal 3d charge delocalization onto the ligands. This net decrease of metal-ligand covalency results in lower metal-centered excited state energies in agreement with previously reported excited state dynamics. Furthermore, traces of solvent-effects were found indicating a varying interaction strength of the solvent with ligands of different character. Our results demonstrate how ligand exchange can be exploited to shape frontier orbitals of transition metal complexes in solution-phase chemistry; insights upon which future efforts can built when tailoring the functionality of photoactive systems for light-harvesting applications.
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| 17. |
- Johansson, Fredrik, et al.
(author)
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Auger- and Photoelectron Coincidences of Molecular O2 Adsorbed on Ag(111)
- 2022
-
In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier. - 0368-2048 .- 1873-2526. ; 256
-
Journal article (peer-reviewed)abstract
- The oxygen on Ag(111) system has been investigated with Auger electron–photoelectron coincidence spectroscopy (APECS). The coincidence spectra between O 1s core level photoelectrons and O KLL Auger electrons have been studied together with Ag3d/AgM4,5NN coincidences. We also describe the electron–electron coincidence spectrometer setup, CoESCA, consisting of two angle resolved time-of-flight spectrometers at a synchrotron light source. Contributions from molecular oxygen and chemisorbed oxygen are assigned using the coincidence data, conclusions are drawn primarily from the O 1s/O KLL data. The data acquisition and treatment procedure are also outlined. The chemisorbed oxygen species observed are relevant for the catalytic ethylene oxidation.
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| 18. |
- Johansson, Fredrik O. L., et al.
(author)
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A Blyholder mechanism in the chemisorption of N2O on Ni(111) : studied with Auger-photoelectron coincidence spectroscopy
- 2024
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In: Applied Surface Science. - : Elsevier. - 0169-4332 .- 1873-5584. ; 666
-
Journal article (peer-reviewed)abstract
- In heterogeneous catalysis the surface-adsorbate bond strength is critical for the function of the system. Here we study a series consisting of multilayer, bilayer and monolayer N2O on Ni(111) and employ Auger-photoelectron coincidence spectroscopy (APECS) to study the interaction between the molecule and the substrate directly. We observe intensity in the nitrogen Auger spectra that arise from the interaction between molecule and surface (not observed in free molecules) whereas the oxygen spectra are thickness-independent. Since the two nitrogen atoms of N2O are chemically inequivalent we can assign the intensity present in the bilayer and monolayer cases to orbitals centered on the terminal nitrogen which is closest to the Ni(111) surface. Using ab initio, molecular dynamics and solid-state density functional theory calculations we infer a Blyholder model of the surface bond as consisting of donation from the terminal nitrogen lone-pair valence orbital with back-donation from the metal into the unoccupied orbitals on that nitrogen. This coincidence technique can readily be used to study substrate–adsorbate interactions directly with chemical and orbital specificity — this opens up prospects to study fundamental steps of molecular adsorption and heterogeneous catalysis with unprecedented detail.
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| 19. |
- Josefsson, Ida, et al.
(author)
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Ab Initio Calculations of X-ray Spectra : Atomic Multiplet and Molecular Orbital Effects in a Multiconfigurational SCF Approach to the L-Edge Spectra of Transition Metal Complexes
- 2012
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In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 3:23, s. 3565-3570
-
Journal article (peer-reviewed)abstract
- A new ab initio approach to the calculation of X-ray spectra is demonstrated. It combines a high-level quantum chemical description of the chemical interactions and local atomic multiplet effects. We show here calculated L-edge X-ray absorption (XA) and resonant inelastic X-ray scattering spectra for aqueous Ni2+ and XA spectra for a polypyridyl iron complex. Our quantum chemical calculations on a high level of accuracy in a post-Hartree–Fock framework give excellent agreement with experiment. This opens the door to reliable and detailed information on chemical interactions and the valence electronic structure in 3d transition-metal complexes also in transient excited electronic states. As we combine a molecular-orbital description with a proper treatment of local atomic electron correlation effects, our calculations uniquely allow, in particular, identifying the influence of interatomic chemical interactions versus intra-atomic correlations in the L-edge X-ray spectra.
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| 20. |
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| 21. |
- Kubin, Markus, et al.
(author)
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Probing the oxidation state of transition metal complexes : a case study on how charge and spin densities determine Mn L-edge X-ray absorption energies
- 2018
-
In: Chem. Sci.. - : The Royal Society of Chemistry. ; 9:33, s. 6813-6829
-
Journal article (peer-reviewed)abstract
- Transition metals in inorganic systems and metalloproteins can occur in different oxidation states, which makes them ideal redox-active catalysts. To gain a mechanistic understanding of the catalytic reactions, knowledge of the oxidation state of the active metals, ideally in operando, is therefore critical. L-edge X-ray absorption spectroscopy (XAS) is a powerful technique that is frequently used to infer the oxidation state via a distinct blue shift of L-edge absorption energies with increasing oxidation state. A unified description accounting for quantum-chemical notions whereupon oxidation does not occur locally on the metal but on the whole molecule and the basic understanding that L-edge XAS probes the electronic structure locally at the metal has been missing to date. Here we quantify how charge and spin densities change at the metal and throughout the molecule for both redox and core-excitation processes. We explain the origin of the L-edge XAS shift between the high-spin complexes MnII(acac)2 and MnIII(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 MnIII 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.
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| 22. |
- Kühn, Danilo, et al.
(author)
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Capabilities of Angle Resolved Time of Flight electron spectroscopy with the 60 degrees wide angle acceptance lens
- 2018
-
In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier. - 0368-2048 .- 1873-2526. ; 224, s. 45-50
-
Journal article (peer-reviewed)abstract
- 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.
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| 23. |
- Kunnus, Kristjan, et al.
(author)
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Anti-Stokes resonant x-ray Raman scattering for atom specific and excited state selective dynamics
- 2016
-
In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 18
-
Journal article (peer-reviewed)abstract
- Ultrafast electronic and structural dynamics of matter govern rate and selectivity of chemical reactions, as well as phase transitions and efficient switching in functional materials. Since x-rays determine electronic and structural properties with elemental, chemical, orbital and magnetic selectivity, short pulse x-ray sources have become central enablers of ultrafast science. Despite of these strengths, ultrafast x-rays have been poor at picking up excited state moieties from the unexcited ones. With time-resolved anti-Stokes resonant x-ray Raman scattering (AS-RXRS) performed at the LCLS, and ab initio theory we establish background free excited state selectivity in addition to the elemental, chemical, orbital and magnetic selectivity of x-rays. This unparalleled selectivity extracts low concentration excited state species along the pathway of photo induced ligand exchange of Fe(CO)(5) in ethanol. Conceptually a full theoretical treatment of all accessible insights to excited state dynamics with AS-RXRS with transform-limited x-ray pulses is given-which will be covered experimentally by upcoming transform-limited x-ray sources.
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| 24. |
- Kunnus, Kristjan, et al.
(author)
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From Ligand Fields to Molecular Orbitals : Probing the Local Valence Electronic Structure of Ni2+ in Aqueous Solutions with Resonant Inelastic X-ray Scattering
- 2013
-
In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 117, s. 16512-16521
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Journal article (peer-reviewed)abstract
- Bonding of the Ni2+(aq) complex is investigated with an unprecedented combination of resonant inelastic X-ray scattering (RIXS) measurements and ab initio calculations at the Ni L absorption edge. The spectra directly reflect the relative energies of the ligand-field and charge-transfer valence-excited states. They give element-specific access with atomic resolution to the ground-state electronic structure of the complex and allow quantification of ligand-field strength and 3d–3d electron correlation interactions in the Ni2+(aq) complex. The experimentally determined ligand-field strength is 10Dq = 1.1 eV. This and the Racah parameters characterizing 3d–3d Coulomb interactions B = 0.13 eV and C = 0.42 eV as readily derived from the measured energies match very well with the results from UV–vis spectroscopy. Our results demonstrate how L-edge RIXS can be used to complement existing spectroscopic tools for the investigation of bonding in 3d transition-metal coordination compounds in solution. The ab initio RASPT2 calculation is successfully used to simulate the L-edge RIXS spectra.
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| 25. |
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| 26. |
- Norell, Jesper, et al.
(author)
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Fingerprints of electronic, spin and structural dynamics from resonant inelastic soft X-ray scattering in transient photo-chemical species
- 2018
-
In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 20:10, s. 7243-7253
-
Journal article (peer-reviewed)abstract
- We describe how inversion symmetry separation of electronic state manifolds in resonant inelastic soft X-ray scattering (RIXS) can be applied to probe excited-state dynamics with compelling selectivity. In a case study of Fe L-3-edge RIXS in the ferricyanide complex Fe(CN)(6)(3-), we demonstrate with multi-configurational restricted active space spectrum simulations how the information content of RIXS spectral fingerprints can be used to unambiguously separate species of different electronic configurations, spin multiplicities, and structures, with possible involvement in the decay dynamics of photo-excited ligand-to-metal charge-transfer. Specifically, we propose that this could be applied to confirm or reject the presence of a hitherto elusive transient Quartet species. Thus, RIXS offers a particular possibility to settle a recent controversy regarding the decay pathway, and we expect the technique to be similarly applicable in other model systems of photo-induced dynamics.
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| 27. |
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| 28. |
- Savchenko, Viktoriia, et al.
(author)
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Vibrational resonant inelastic X-ray scattering in liquid acetic acid : a ruler for molecular chain lengths
- 2021
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In: Scientific Reports. - : Springer Nature. - 2045-2322. ; 11:1
-
Journal article (peer-reviewed)abstract
- Quenching of vibrational excitations in resonant inelastic X-ray scattering (RIXS) spectra of liquid acetic acid is observed. At the oxygen core resonance associated with localized excitations at the O-H bond, the spectra lack the typical progression of vibrational excitations observed in RIXS spectra of comparable systems. We interpret this phenomenon as due to strong rehybridization of the unoccupied molecular orbitals as a result of hydrogen bonding, which however cannot be observed in x-ray absorption but only by means of RIXS. This allows us to address the molecular structure of the liquid, and to determine a lower limit for the average molecular chain length.
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| 29. |
- Schreck, Simon, et al.
(author)
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Ground state potential energy surfaces around selected atoms from resonant inelastic x-ray scattering.
- 2016
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
-
Journal article (peer-reviewed)abstract
- Thermally driven chemistry as well as materials' functionality are determined by the potential energy surface of a systems electronic ground state. This makes the potential energy surface a central and powerful concept in physics, chemistry and materials science. However, direct experimental access to the potential energy surface locally around atomic centers and to its long-range structure are lacking. Here we demonstrate how sub-natural linewidth resonant inelastic soft x-ray scattering at vibrational resolution is utilized to determine ground state potential energy surfaces locally and detect long-range changes of the potentials that are driven by local modifications. We show how the general concept is applicable not only to small isolated molecules such as O2 but also to strongly interacting systems such as the hydrogen bond network in liquid water. The weak perturbation to the potential energy surface through hydrogen bonding is observed as a trend towards softening of the ground state potential around the coordinating atom. The instrumental developments in high resolution resonant inelastic soft x-ray scattering are currently accelerating and will enable broad application of the presented approach. With this multidimensional potential energy surfaces that characterize collective phenomena such as (bio)molecular function or high-temperature superconductivity will become accessible in near future.
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| 30. |
- Schröder, Henning, et al.
(author)
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Varying photo-dissociation mechanisms in Fe(CO)5 and Cr(CO)6 from femtosecond valence photoemission and excited-state moleculardynamics simulations
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Other publication (other academic/artistic)abstract
- We present measured and calculated time-resolved photoelectron spectra of photoexcited gas-phase Fe(CO)5 and Cr(CO)6. Upon electronic excitation with 266 nm pump pulses and by probing with 23 eV photons from a femtosecond high-order har-monic generation source, we observe differences between Fe(CO)5 and Cr(CO)6 that indicate that the excited-state and dissociation dynamics are slower in Fe(CO)5 than in Cr(CO)6. Changing photoelectron intensities and binding energies combined with excited-state molecular dynamics simulations indicate repopulations of excited states from bound excited to dissociative excited states and to the dissociated species. We find that the more open and flexible structure of Fe(CO)5 with larger metal-carbonyl angles enables the photoexcited states of Fe(CO)5 to dissipate energy by angular distortions as observed in longer populations of bound excited states. The more compactand closed structure of Cr(CO)6 does not enable this relaxation resulting in fasterdissociation.
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| 31. |
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| 32. |
- Sun, Yu-Ping, et al.
(author)
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Interference between Resonant and Nonresonant Inelastic X-Ray Scattering
- 2013
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 110:22, s. 223001-
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Journal article (peer-reviewed)abstract
- A detailed study of inelastic x-ray scattering from the ground state to the Σg3(3σg-13sg1) state of the O2 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.
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| 33. |
- Söderström, Johan, 1978-, et al.
(author)
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Resonant inelastic x-ray scattering on CO2 : Parity conservation in inversion-symmetric polyatomics
- 2020
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 101:6
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Journal article (peer-reviewed)abstract
- Resonant inelastic x-ray scattering (RIXS) spectra excited at the oxygen K edge of CO2 are presented and discussed. Although excitation from a gerade initial state to the intermediate 1s-1π* state breaks the inversion symmetry due to strong vibronic coupling, RIXS excited at the corresponding resonance exclusively populates gerade vibrations in the gerade electronic ground state. This observation constitutes an experimental confirmation of the prediction that the parity selection rule applies in RIXS on an inversion-symmetric polyatomic system, provided that the total electronic-vibronic wave function is considered. Parity selectivity is used for assigning spectra to the population of electronically excited final states, a procedure hampered only when symmetry-breaking vibronic coupling in the final states is prominent. A RIXS spectrum excited in the Rydberg region is tentatively assigned using a simplified quasi-two-step model in which it is assumed that the electron in the Rydberg orbital excited in the first step remains as a spectator during the second decay step.
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| 34. |
- Vaz da Cruz, Vinicius, 1987-, et al.
(author)
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A study of the water molecule using frequency control over nuclear dynamics in resonant X-ray scattering
- 2017
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 19:30, s. 19573-19589
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Journal article (peer-reviewed)abstract
- In this combined theoretical and experimental study we report a full analysis of the resonant inelastic X-ray scattering (RIXS) spectra of H2O, D2O and HDO. We demonstrate that electronically-elastic RIXS has an inherent capability to map the potential energy surface and to perform vibrational analysis of the electronic ground state in multimode systems. We show that the control and selection of vibrational excitation can be performed by tuning the X-ray frequency across core-excited molecular bands and that this is clearly reflected in the RIXS spectra. Using high level ab initio electronic structure and quantum nuclear wave packet calculations together with high resolution RIXS measurements, we discuss in detail the mode coupling, mode localization and anharmonicity in the studied systems.
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| 35. |
- Vaz da Cruz, Vinicius, et al.
(author)
-
A study of the water molecule using frequency control over nuclear dynamics in resonant X-ray scattering
- 2017
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:30, s. 19573-19589
-
Journal article (peer-reviewed)abstract
- In this combined theoretical and experimental study we report a full analysis of the resonant inelastic X-ray scattering (RIXS) spectra of H2O, D2O and HDO. We demonstrate that electronically-elastic RIXS has an inherent capability to map the potential energy surface and to perform vibrational analysis of the electronic ground state in multimode systems. We show that the control and selection of vibrational excitation can be performed by tuning the X-ray frequency across core-excited molecular bands and that this is clearly reflected in the RIXS spectra. Using high level ab initio electronic structure and quantum nuclear wave packet calculations together with high resolution RIXS measurements, we discuss in detail the mode coupling, mode localization and anharmonicity in the studied systems.
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| 36. |
- Vaz da Cruz, Vinicius, et al.
(author)
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Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering
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Other publication (other academic/artistic)abstract
- The potential energy surface is widely used powerful concept in chemical physics. However, direct experimental access to the local potential energy surface in liquid especially in systems with strong hydrogen bonds is lacking. We develop general technique demonstrated for liquid water how to reconstruct from state-of-the-art sub-natural linewidth resonant inelastic X-ray scattering (RIXS) the local distribution of OH potential energy curves, separately for OH bonds with weak and strong hydrogen bond. By this we are able to look on the local structure by characterising selectively the strength of the hydrogen bond. We present a detailed analysis of the formation of the vibrationally resolved RIXS of liquids using a classical/quantum formalism based on a combination of {\it ab initio} molecular dynamics, density functional theory calculations and quantum nuclear wave packet propagation. Theory nicely explains shortening of the vibrational progression in liquid phase in comparison with RIXS of free water molecules seen in the experiment by fluctuation of the hydrogen bond network and coherent excitation of both OH bonds.
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| 37. |
- Vaz da Cruz, Vinicius, et al.
(author)
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Resonant inelastic X-ray scattering and X-ray absorption of methanol at the near oxygen K-edge
-
Other publication (other academic/artistic)abstract
- We report on a theoretical analysis of core-excitation spectra of gas and liquid phase methanol asobtained with use of X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering(RIXS). The electronic transitions are studied with complementary computational methods includ-ing strict and extended second-order algebraic diagrammatic construction (ADC(2) and ADC(2)-x),restricted active space second-order perturbation theory (RASPT2), and time-dependent densityfunctional theory (TDDFT)—providing a complete assignment of the near oxygen K-edge XAS.We show that multimode nuclear dynamics is of crucial importance for explaining the availableexperimental XAS and RIXS spectra. Multimode nuclear motions was considered in a developedmixed representation where dissociative states and highly excited vibrational modes are accuratelytreated with a time-dependent wave packet technique while the remaining active vibrational modesare described using Franck–Condon amplitudes. Particular attention is paid to the polarizationdependence of RIXS and the effects of the isotope substitution on the RIXS profile in the case ofdissociative core-excited states. Our approach predicts the splitting of the 2a RIXS peak to bedue to an interplay between molecular and atomic-like features arising in the course of transitionsbetween dissociative core- and valence-excited states. The dynamical nature of the splitting of the2a peak in RIXS of liquid methanol near pre-edge core excitation is shown. The theoretical resultsare in good agreement with available experimental data.
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| 38. |
- Wernet, Philippe, et al.
(author)
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Dissecting Local Atomic and Intermolecular Interactions of Transition-Metal Ions in Solution with Selective X-ray Spectroscopy
- 2012
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In: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 3:23, s. 3448-3453
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Journal article (peer-reviewed)abstract
- Determining covalent and charge-transfer contributions to bonding in solution has remained an experimental challenge. Here, the quenching of fluorescence decay channels as expressed in dips in the L-edge X-ray spectra of solvated 3d transition-metal ions and complexes was reported as a probe. With a full set of experimental and theoretical ab initio L-edge X-ray spectra of aqueous Cr3+, including resonant inelastic X-ray scattering, we address covalency and charge transfer for this prototypical transition-metal ion in solution. We dissect local atomic effects from intermolecular interactions and quantify X-ray optical effects. We find no evidence for the asserted ultrafast charge transfer to the solvent and show that the dips are readily explained by X-ray optical effects and local atomic state dependence of the fluorescence yield. Instead, we find, besides ionic interactions, a covalent contribution to the bonding in the aqueous complex of ligand-to-metal charge-transfer character
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| 39. |
- Wernet, Philippe, 1971-, et al.
(author)
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Orbital-specific mapping of the ligand exchange dynamics of Fe(CO)5 in solution
- 2015
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 520:7545, s. 78-81
-
Journal article (peer-reviewed)abstract
- Transition-metal complexes have long attracted interest for fundamental chemical reactivity studies and possible use in solar energy conversion. Electronic excitation, ligand loss from the metal centre, or a combination of both, creates changes in charge and spin density at the metal site that need to be controlled to optimize complexes for photocatalytic hydrogen production and selective carbon-hydrogen bond activation. 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 insolution, that the photoinduced removal of CO generates the 16-electron Fe(CO)4 species, a homogeneous catalyst with an electron deficiency at the Fe centre, 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, 16,17,18,19 and 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.
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| 40. |
- Aad, G., et al.
(author)
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- 2011
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Journal article (peer-reviewed)
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