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Author ORCID ID is 0000000239242993
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  1. 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 themore » valence-orbital interactions upon Fe–CO dissociation, thereby validating fundamental theoretical concepts in Fe–CO bonding. Chemical shifts of CO 3σ inner-valence and Fe 3p 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. Lastly, it could also serve as a benchmark for how charge and spin density changes in molecular dissociation and excited-state dynamics are expressed in valence and core-level photoelectron spectroscopy.« less
  2. 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. π-Back-donation is found to be mainly determined by themore » metal site occupation, whereas the ligand hole instead influences σ-donation. Here, 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.« less
  3. Cited by 18Full Text Available
  4. Here, 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 timescale.

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