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.

Diabatic free energy curves and coordination fluctuations for the aqueous Ag+∕Ag2+ redox couple: A biased Born-Oppenheimer molecular dynamics investigation

“…Quantitative comparison is further complicated by the fact that the experimental estimate of Ref. 58 was obtained for solutions of relatively high concentration. We are confident, however, that the nonlinear behavior found for the Ag + /Ag 2+ remains valid in the limit of infinite dilution.…”

“…In this regard, a very interesting experimental method relates the ionization threshold of ionic solutions to single-ion reorganization free energies. 58 According to Delahay and Dziedzic the ionization threshold E t is a good estimate for the sum of absolute oxidation free enthalpy ⌬G of a redox half reaction and the single-ion reorganization free energy of the oxidized state O , O , E t Ϸ ⌬G + O + ͉e͉⌬, where ⌬ is a small and negligible correction factor accounting for different surface potentials. ⌬G can be obtained from the experimental oxidation potential ⑀ ox 0 of the half reaction ͑⌬G conv =−F⑀ ox 0 ͒ if an absolute value for the oxidation free enthalpy ⌬G H of the hydrogenhydrogenium reaction 1 / 2H 2g → H aq + + e g − is assumed, ⌬G = ⌬G conv + ⌬G H .…”

The ejection distribution of solvated electrons generated by the one-photon photodetachment of aqueous I− and two-photon ionization of the solvent

“…1͒. 6,7 It is the subsequent steps in the mechanism of Eq. ͑1͒, the rapid destruction of the CTTS state, as the solvent rearranges around the new charge density leading to electron ejection into the solvent, that are controversial.…”

Electron transfer reactivity of methyl‐substituted amine NHn(CH3)3−n/NHn(CH3) (n = 0–3) self‐exchange systems: a theoretical investigation

“…In the last two decades, ET reactions have continued to be the subject of many theoretical [6][7][8] and experimental [9][10][11] studies, for both chemical and biological systems. In general, ET can occur in a determinate range of contact distances, although there is a maximum reaction probability for each ET system at an optimum contact distance.…”