Well and barrier dynamics and electron transfer rates. A molecular dynamics study

Abstract

Molecular dynamics simulations are carried out for model electronically adiabatic electron transfer (ET) reactions. The reactants are immersed in various model dipolar aprotic solvents, ranging from slightly overdamped to strongly overdamped. In all cases, the solvent barrier recrossings which give the solvent dynamical influence on the ET rate are determined by motion in the barrier top region, and not in the solvent wells as some current notions would have it. The MD reaction transmission coefficients are reproduced by Grote-Hynes theory to within the simulation error bars, while other analytic descriptions such as Zusman theory (in its range of applicability) and Kramers theory are less satisfactory, and fail significantly in the overdamped solvent regime. The reasons for these results as well as their implications for the interpretation of adiabatic ET rates are briefly discussed.