title: Photooxidation and photoaquation of iron hexacyanide in aqueous solution: A picosecond X-ray absorption study.
abstract: We present a picosecond Fe K-edge absorption study of photoexcited ferrous and ferric hexacyanide in water under 355 and 266 nm excitation. Following 355 nm excitation, the transient spectra for the ferrous and ferric complexes exhibit a red shift of the edge reflecting an increased electron density at the Fe atom. For the former, an enhanced pre-edge transition is also observed. These observations are attributed to the aquated [Fe(CN)5OH2](3-) species, based on quantum chemical calculations which also provide structural parameters. Upon 266 nm excitation of the ferric complex, a transient reminiscent of the aquated species is observed (appearance of a pre-edge feature and red shift of the edge) but it is different from that obtained under 355 nm excitation. This points to a new reaction channel occurring through an intermediate state lying between these two excitation energies. Finally, 266 nm excitation of the ferrous species is dominated by the photooxidation channel with formation of the ferric complex as main photoproduct. However, we observe an additional minor photoproduct, which is identical to the 266 nm generated photoproduct of the ferric species, suggesting that under our experimental conditions, the pump pulse photooxidises the ferrous complex and re-excites the primary ferric photoproduct.
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Spectroscopie Ultrarapide , ISIC, FSB, CH-1015 Lausanne, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Reinhard
authors.forename: T J
authors.initials: TJ
authors.lastname: Penfold
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Spectroscopie Ultrarapide , ISIC, FSB, CH-1015 Lausanne, Switzerland.
authors.forename: F A
authors.initials: FA
authors.lastname: Lima
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Spectroscopie Ultrarapide , ISIC, FSB, CH-1015 Lausanne, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Rittmann
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Spectroscopie Ultrarapide , ISIC, FSB, CH-1015 Lausanne, Switzerland.
authors.forename: M H
authors.initials: MH
authors.lastname: Rittmann-Frank
authors.affiliation: SwissFEL, Paul Scherrer Inst , CH-5232 Villigen, Switzerland.
authors.forename: R
authors.initials: R
authors.lastname: Abela
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Chimie et Biochimie Computationnelles , ISIC, FSB, CH-1015 Lausanne, Switzerland.
authors.forename: I
authors.initials: I
authors.lastname: Tavernelli
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Chimie et Biochimie Computationnelles , ISIC, FSB, CH-1015 Lausanne, Switzerland.
authors.forename: U
authors.initials: U
authors.lastname: Rothlisberger
authors.forename: C J
authors.initials: CJ
authors.lastname: Milne
authors.affiliation: Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Spectroscopie Ultrarapide , ISIC, FSB, CH-1015 Lausanne, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Chergui