Reaction dynamics on a thermally fluctuating potential

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