title: Ultraviolet photochemical reaction of [Fe(III)(C2O4)3](3-) in aqueous solutions studied by femtosecond time-resolved X-ray absorption spectroscopy using an X-ray free electron laser.
abstract: Time-resolved X-ray absorption spectroscopy was performed for aqueous ammonium iron(III) oxalate trihydrate solutions using an X-ray free electron laser and a synchronized ultraviolet laser. The spectral and time resolutions of the experiment were 1.3 eV and 200 fs, respectively. A femtosecond 268 nm pulse was employed to excite [Fe(III)(C2O4)3](3-) in solution from the high-spin ground electronic state to ligand-to-metal charge transfer state(s), and the subsequent dynamics were studied by observing the time-evolution of the X-ray absorption spectrum near the Fe K-edge. Upon 268 nm photoexcitation, the Fe K-edge underwent a red-shift by more than 4 eV within 140 fs; however, the magnitude of the redshift subsequently diminished within 3 ps. The Fe K-edge of the photoproduct remained lower in energy than that of [Fe(III)(C2O4)3](3-). The observed red-shift of the Fe K-edge and the spectral feature of the product indicate that Fe(III) is upon excitation immediately photoreduced to Fe(II), followed by ligand dissociation from Fe(II). Based on a comparison of the X-ray absorption spectra with density functional theory calculations, we propose that the dissociation proceeds in two steps, forming first [(CO2 (•))Fe(II)(C2O4)2](3-) and subsequently [Fe(II)(C2O4)2](2-).
authors.affiliation: Molecular Reaction Dynamics Research Team, RIKEN Center for Advanced Photonics , 2-1 Hirosawa, Wako 351-0198, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Ogi
authors.forename: Y
authors.initials: Y
authors.lastname: Obara
authors.affiliation: Japan Synchrotron Radiation Research Institute , 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Katayama
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University , Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Y-I
authors.initials: YI
authors.lastname: Suzuki
authors.affiliation: Molecular Reaction Dynamics Research Team, RIKEN Center for Advanced Photonics , 2-1 Hirosawa, Wako 351-0198, Japan.
authors.forename: S Y
authors.initials: SY
authors.lastname: Liu
authors.affiliation: Molecular Reaction Dynamics Research Team, RIKEN Center for Advanced Photonics , 2-1 Hirosawa, Wako 351-0198, Japan.
authors.forename: N C-M
authors.initials: NC
authors.lastname: Bartlett
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University , Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Kurahashi
authors.affiliation: Department of Chemistry, Graduate School of Science, Kyoto University , Kitashirakawa-Oiwakecho, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Karashima
authors.affiliation: Japan Synchrotron Radiation Research Institute , 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Togashi
authors.affiliation: Japan Synchrotron Radiation Research Institute , 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Inubushi
authors.affiliation: RIKEN SPring-8 Center , 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Ogawa
authors.affiliation: RIKEN SPring-8 Center , 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Owada
authors.affiliation: Department of Physical Chemistry, University of Chemistry and Technology , Technická 5, Prague 6 16628, Czech Republic.
authors.forename: M
authors.initials: M
authors.lastname: Rubešová
authors.affiliation: RIKEN SPring-8 Center , 1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5148, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Yabashi
authors.forename: K
authors.initials: K
authors.lastname: Misawa
authors.affiliation: Department of Physical Chemistry, University of Chemistry and Technology , Technická 5, Prague 6 16628, Czech Republic.
authors.forename: P
authors.initials: P
authors.lastname: Slavíček
authors.forename: T
authors.initials: T
authors.lastname: Suzuki