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  Leitner, T.; Josefsson, I.; Mazza, T.; Miedema, P.; Schröder, H.; Beye, M.; Kunnus, K.; Schreck, S.; Düsterer, S.; Föhlisch, A.; Meyer, M.; Odelius, M.; Wernet, P.: Time-resolved electron spectroscopy for chemical analysis of photodissociation: Photoelectron spectra of Fe(CO)₅, Fe(CO)₄, and Fe(CO)₃. The Journal of Chemical Physics 149 (2018), p. 044307/1-12

10.1063/1.5035149
Open Access Version

Abstract:
The Q2 prototypical photoinduced dissociation of Fe(CO)5 in the gas phase is used to test time-resolved x-ray photoelectron spectroscopy for studying photochemical reactions. Upon one-photon excitation at 266 nm, Fe(CO)5 successively dissociates to Fe(CO)4 and Fe(CO)3 along a pathway where both fragments retain the singlet multiplicity of Fe(CO)5. The x-ray free-electron laser FLASH is used to probe the reaction intermediates Fe(CO)4 and Fe(CO)3 with time-resolved valence and core-level photoelectron spectroscopy, and experimental results are interpreted with ab initio quantum chemical calculations. Changes in the valence photoelectron spectra are shown to reflect changes in the valenceorbital interactions upon Fe–CO dissociation, thereby validating fundamental theoretical concepts in Fe–CO bonding. Chemical shifts of CO 3 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. It could also serve as a benchmark for howcharge and spin density changes in molecular dissociation and excited-state dynamics are expressed in valence and core-level photoelectron spectroscopy.