Reaction dynamics on a thermally fluctuating potential

This paper analyzes the kinetics of escape of a particle over a barrier flu ctuating between two states, the fluctuations being produced by thermal noi se. By this we mean that the jump rates for transitions between the two sta tes are position-dependent, satisfying detailed balance at any point along the reaction coordinate. The fast-fluctuation limit can be analyzed in term s of the potential of mean force, and for high barriers the survival probab ility is found to be a single exponential. In the slow-fluctuation regime t he survival probability is a linear combination of two exponentials. In the case of a linear potential the slow-fluctuation solution describes the kin etics, as obtained from simulations, quite well over the entire range of th e jump rates between the two states. Our analysis suggests that this is tru e for more general forms of the potential. Further, for a thermally fluctua ting potential the mean lifetime is shown to decrease monotonically as the jump rate increases. This is in contrast to the turnover behavior, or reson ant activation, which can occur when fluctuations are produced by nontherma l noise. An extension of our approach to systems with thermal fluctuations between more than two states is discussed. (C) 1999 American Institute of P hysics. [S0021-9606(99)52345-3].