Classical solvent dynamics and electron transfer. II. Molecular aspects

Abstract

Charge transferreactions in polar solvents are accompanied by reorganization of the solvent. In many cases, the dynamics of this reorganization determines the rate for charge transfer. In this paper the dynamics of this process is investigated with special emphasis on the molecular nature of the solvent. The reaction coordinate is identified and an equation of motion for this coordinate is derived. The equation describes the diffusion of the reaction coordinate in a bistable potential, which can be treated using Kramers’ theory. The form of the bistable potential is discussed in detail, with special emphasis on the distinction between this effective potential and a nonequilibrium free energy. As an example the resulting expressions for the rate of electron transfer between the charged and uncharged states of a zwitterion are calculated using a simple, approximate model for the fluid structure. The difference between these results and those from the continuum dielectric treatment of the solvent are discussed.