THEORETICAL-STUDY OF ELECTRONIC TRANSMISSION COEFFICIENT OF OUTER-SPHERE ELECTRON SELF-EXCHANGE REACTIONS IN SOLUTION - A HYDRATION FUNCTION SCHEME

On the basis of the thermodynamic characteristics of the hydration pro cess of metal ions, a new theoretical scheme is presented. It is appli ed to determining the theoretical values of the electronic transmissio n coefficient of electron self-exchange reactions in solution in terms of the original Landau-Zener formalism. This scheme gets around the s hortcomings of the summation method of the inner-sphere and outer-sphe re contributions and directly adopts accurate hydration potential func tions to determine relevant quantities. The hydration potential functi ons are analytically determined from the experimental spectroscopic da ta and the hydration energy data, Two important quantities are the slo pes of the potential energy surfaces and the coupling matrix elements. The slopes are obtained from the hydration potential functions and th e activation parameters are obtained in terms of a new proposed self-e xchange activation model. The coupling matrix elements are determined from adiabatic and diabatic activation energies which are obtained fro m the new activation model and experiment, and are compared with the a b initio values in recent literature. Theoretical results of the elect ronic transmission coefficients of electron transfer reactions obtaine d using the values of slopes from the hydration potential functions ar e found to be in close agreement with the corresponding experimental v alues obtained from the experimental rate data. These theoretical valu es of the electronic transmission coefficient and the experimental val ues are found to be less than unity. This indicates that outer-sphere electron transfer reactions in solution involving hydrated transition metal ions studied in this work are nonadiabatic in nature. The applic ability of this scheme is also discussed. (C) 1997 Elsevier Science B. V.