Inner-sphere reorganization in optical electron transfer

Abstract

Free energies for photoelectron emission by aqueous solutions of hexaquo cations (V2+, Cr2+, Fe2+), metal complexes [Fe(CN)4−6, Co(NH3)2+6], and inorganic anions (OH−, Cl−, Br−, I−) are calculated from theory and compared with experimental threshold energies. Good agreement is obtained within the estimated error (±0.2 eV) on emission free energies. The free energy for outer-sphere reorganization is calculated from a continuous medium model. The inner-sphere reorganization energy is obtained from a bond-stretching model for hexaquo cations and metal complexes. A new method is developed for the calculation of the inner-sphere reorganization energies of univalent anions from their free energies of hydration. Reorganization free energies for electron transfer reactions [V2+/3+, Cr2+/3+, Mn2+/3, Fe2+/3+, Fe(CN)4−/3−6 ] calculated from experimental threshold energies and computed outer-sphere reorganization free energies yield activation free energies in agreement with the values obtained from kinetic measurements. Improvements are discussed for the determination of threshold energies by extrapolation.