SOLVENT STRUCTURE AND HYDRODYNAMIC EFFECTS IN PHOTOINDUCED ELECTRON-TRANSFER

A previously developed statistical mechanical theory describing photo- induced electron transfer and geminate recombination in liquid solutio ns has been modified to account for realistic finite-volume solvent ef fects. This work introduces physically important effects caused by the solvent which fundamentally affect the rates and spatial distribution of charge transfer events. The finite volume of solvent molecules giv es rise to a nonuniform distribution of particles around an electron d onor, which is incorporated into the theory by a two-particle radial d istribution function (rdf). The Percus-Yevick solutions for the rdf ca n give numerically useful values for the solvent structure, g(R) altho ugh any form of g(R) can be used with the method. The nonuniform parti cle distribution significantly affects the electron transfer rates and the distribution of ion pairs formed by forward electron transfer, pa rticularly at short times. In addition, finite solvent size affects th e rate of relative diffusion between any donor-acceptor pair. These '' hydrodynamic effects'' slow down the interparticle diffusion rates whe n near contact, resulting in a major change in the long time behavior of photoexcited electron transfer systems. This work formally introduc es the mathematical modifications to charge transfer theory necessary to account for the solvent structure and hydrodynamic effect and illus trates the results with model calculations. These calculations show th at analysis of experiments with theories that do not include the rdf a nd hydrodynamic effects can result in significant errors in the interp retation of data. (C) 1996 American Institute of Physics.