Direct evaluation of the electron transfer integral for self-exchange reactions in solution

Abstract

This paper presents several new theoretical schemes for experimentally determining the electronic coupling matrix element of the self-exchange electron transfer reactions between hydrated redox ion pairs in solution by using the experimental electron transfer rate data. The activation energies are determined by using a new hydration potential function model proposed here in which the potential energy surfaces are obtained by fitting the relevant thermodynamic data with an analytical function. The results have shown that the accurate and approximate schemes in the limit of weak electronic coupling are very valid in determining the electron transfer coupling matrix element of the self-exchange reactions in solution. Although inclusion of the Newton approximation may slightly decrease the values of the coupling matrix element, they are still in good agreement with those from the accurate method and the other theoretical methods. The implication that the value of the coupling matrix element is small for this system (<100 cm −1) is that the electron transfer reactions between the hydrated ion pairs in solution are nonadiabatic in nature.