Outer-sphere electron transfer reactions in non-Debye solvents. Theory and numerical results

Abstract

In this paper we present a theory that predicts, for a wide range of reaction adiabaticity, the time evolution of the reactants' population, σR(t), for outer-sphere electron transfer reactions in polar solvents exhibiting a non-Debye relaxation behavior. A number of stochastic trajectory studies have been performed to test the validity of the theory in the limit where solvent relaxation constitutes the rate-limiting step. The agreement between the numerical and theoretical results is excellent. The theory is then used to study a number of different reactive regimes ranging from nonadiabatic to solvent-controlled adiabatic limits. The studies performed show that the character of the decay of σR(t) for low activation barrier reactions constitutes a useful qualitative way of identifying a priori the dielectric relaxation properties of the solvent: For a non-Debye solvent the decay σR (t) is strongly nonexponential in contrast to the results for Debye solvents where σR (t) decays mainly exponentially. The solvent relaxation time scales that are important for the reaction kinetics are identified. Our results are also expressed in terms of rate kernels. For high energy barriers the Stable States Picture results for the forward and reverse rate constants are recovered. © 1989 American Institute of Physics.