Aspects of Aqueous Iron and Manganese (II/III) Self-Exchange Electron Transfer Reactions

Abstract

Ab initio methods were applied to the calculation of the reorganization energy λ and the electronic coupling matrix element VAB for the outer-sphere Fe(OH2)6II/III and Mn(OH2)6II/III self-exchange electron transfer (ET) reactions. For the Fe case, we find an appreciable effect on VAB depending on whether the minority spin electron occupies the dxy orbital or a mixture of dxz/dyz orbitals in the FeII ion. While these two possible nearly isoenergetic electron accepting states alter the magnitude and distance dependence of VAB, they do not affect the internal reorganization energy λI to any significant level. The magnitude and distance dependence of VAB are found to be strongly dependent on encounter orientation, as expected. VAB values for corner-to-corner encounter orientations are substantially larger at any given ET distance considered than those for face-to-face encounter orientations. Values of the decay parameter β are in good agreement with well-accepted values. The adiabaticity criterion is tied to orientation and distance dependence of VAB.