PHOTOINDUCED ELECTRON-TRANSFER AND GEMINATE RECOMBINATION IN LIQUIDS - ANALYTICAL THEORY AND MONTE-CARLO SIMULATIONS

Photoinduced electron transfer and geminate recombination in liquid so lution are addressed with analytical theory and Monte Carlo simulation s. The time-dependent probabilities of the donor being excited and of an ion pair existing are obtained for a system of a donor and many acc epters undergoing diffusive motion. Multiparticle simulations are mode led as a Markov chain and are shown to agree with the analytical forma lism presented previously. The calculations are performed using both a simple exponential form of the distance dependence of the transfer ra te and using the more general Marcus distance-dependent transfer rate. For a static donor, in the absence of acceptor-acceptor excluded volu me, theory and simulations provide identical results, confirming the a ccuracy of the analytical method. For the calculation of properties of real systems in which both the donor and accepters diffuse, to make t he mathematics tractable, the donor is held static and each acceptor i s given a Fick diffusion constant equal to the sum of the diffusion co nstants of the donor and acceptor, D=D-d+ D-a. The validity of this ap proximation is examined in the absence of acceptor-acceptor excluded v olume and found to work extremely well under all conditions. It is als o examined with acceptor-acceptor excluded volume. In this case, the s tatic donor approximation is found to work generally well up to modera tely high acceptor concentrations, <5% packing fraction. However, the results suggest that at even higher packing fractions, the static dono r approximation loses its validity. (C) 1995 American Institute of Phy sics.