Smooth landscape solvent dynamics in electron transfer reactions

Solvent effects play a major role in controlling electron-transfer reaction s. The solvent dynamics happens on a very high-dimensional surface, and thi s complex landscape is populated by a large number of minima. A critical pr oblem is to understand the conditions under which the solvent dynamics can be represented by a single collective reaction coordinate. When this unidim ensional representation is valid, one recovers the successful Marcus theory . In this study the approach used in a previous work [V. B. P. Leite and J. N. Onuchic; J. Phys. Chem. 100, 7680 (1996)] is extended to treat a more r ealistic solvent model, which includes energy correlation. The dynamics tak es place in a smooth and well behaved landscape. The single shell of solven t molecules around a cavity is described by a two-dimensional system with p eriodic boundary conditions with nearest neighbor interaction. It is shown how the polarization-dependent effects can be inferred. The existence of ph ase transitions depends on a factor gamma proportional to the contribution from the two parameters of the model. For the present model, gamma suggests the existence of "weak kinetic phase transitions," which are used in the a nalysis of solvent effects in charge-transfer reactions. (C) 1999 American Institute of Physics. [S0021-9606(99)50420-0].