Electron transfer reactions in solvent mixtures:: the excess component of solvent reorganization free energy

In this payer, experimental and simulation results corresponding to studies of electron transfer processes in solvent mixtures are presented. The methodology is presented to obtain the relevant parameters controlling the elementary electron transfer step, namely, the reorganization free energy, lambda, and the driving force, Delta G(o'). It is shown that in solvent mixtures there appears an additional component of the solvent reorganization free energy. An attempt is carried out to quantify its magnitude. The conclusions corresponding to the existence and origin of this extra component are supported by the results of Monte Carlo simulations. It is concluded that continuum models of the solvent, in particular Marcus' model, can give good results for a single component solvent if the critical parameters, the ion sizes, are taken as adjustable parameters and fitted accordingly. However, when these fitted values are used in solvent mixtures, the continuum model fails, even in the absence of any specific solvent effects. (C) 2000 Elsevier Science S.A. All rights reserved.