title: Valence photoemission spectra of aqueous Fe(2+/3+) and [Fe(CN)6](4-/3-) and their interpretation by DFT calculations.
abstract: Aqueous solutions of ferrous and ferric iron (Fe(2+/3+)) and of the iron-hexacyano complexes [Fe(CN)(6)](4-/3-) are studied by photoelectron spectroscopy using a liquid microjet in conjunction with synchrotron soft X-rays for ionization. For Fe(2+)(aq) we observe two well-resolved peaks at 7.09 and 9.16 eV electron binding energy (BE) that can be assigned to the iron-hexaaquo complex. For Fe(3+)(aq) we observe only one peak above the highest valence band of liquid water, at 10.08 eV BE. Interpreting the spectra in terms of the one-electron levels of Kohn-Sham density functional theory, we find that the two peaks for Fe(2+)(aq) originate from the energy splitting between the highest occupied β (= minority) spin level (Fe d(t(2g))) and the five highest occupied α (= majority) spin levels (Fe d(t(2g)) and d(e(g))). The peak for Fe(3+)(aq) arises from d-levels that are strongly mixed with the solvent. The spectra of the aqueous hexacyano complexes show a single strong peak at 6.11 and 7.52 eV BE for [Fe(CN)(6)](4-) and [Fe(CN)(6)](3-), respectively, originating from the highest occupied Fe d(t(2g)) levels, and two further peaks at higher BE originating from the cyano ligands. The PE spectra of the reduced aquo and cyano ions are then used to obtain-solely on experimental grounds-values for the reorganization free energy of the oxidized ions. DFT/continuum calculations of this important parameter in the Marcus theory of oxidation reactions are in fairly good agreement with experiment.
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, and BESSY, Albert-Einstein-Strasse 15, D-12489 Berlin, Germany.
authors.forename: Robert
authors.initials: R
authors.lastname: Seidel
authors.forename: Stephan
authors.initials: S
authors.lastname: Thürmer
authors.forename: Jan
authors.initials: J
authors.lastname: Moens
authors.forename: Paul
authors.initials: P
authors.lastname: Geerlings
authors.forename: Jochen
authors.initials: J
authors.lastname: Blumberger
authors.forename: Bernd
authors.initials: B
authors.lastname: Winter
mesh_terms: D056831:Coordination Complexes / Q000737:chemistry*; D005292:Ferricyanides / Q000737:chemistry*; D005295:Ferrocyanides / Q000737:chemistry*; D010084:Oxidation-Reduction; D056951:Photoelectron Spectroscopy; D011789:Quantum Theory; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D056831:Coordination Complexes; D005292:Ferricyanides; D005295:Ferrocyanides; D014867:Water; C007931:hexacyanoferrate III; C020354:hexacyanoferrate II