DIRECT EVALUATION OF THE ELECTRON-TRANSFER INTEGRAL FOR SELF-EXCHANGEREACTIONS IN SOLUTION

This paper presents several new theoretical schemes for experimentally determining the electronic coupling matrix element of the self-exchan ge electron transfer reactions between hydrated redox ion pairs in sol ution by using the experimental electron transfer rate data. The activ ation energies are determined by using a new hydration potential funct ion model proposed here in which the potential energy surfaces are obt ained by fitting the relevant thermodynamic data with an analytical fu nction. The results have shown that the accurate and approximate schem es in the limit of weak electronic coupling are Very valid in determin ing 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 t he other theoretical methods. The implication that the value of the co upling matrix element is small for this system ( < 100 cm(-1)) is that the electron transfer reactions between the hydrated ion pairs in sol ution are nonadiabatic in nature. (C) 1998 Elsevier Science B.V. All r ights reserved.