Non-monotonic dependence of electronic relaxation rate on solvent viscosity

Abstract

Electronic relaxation processes in solution in which intramolecular potential barriers to reactive motion are absent are modelled by brownian motion of a solute particle on a harmonic surface with a position-dependent sink. The resulting Fokker-Planck equation with the sink term is solved by generating stochastic trajectories. We find that the rate constant for population decay is a non-monotonic, function of solvent friction. The Smoluchowski equation is found to overestimate the rate significantly in the low-friction regime.