QUANTUM EFFECTS IN BARRIER DYNAMICS

The dynamics near the top of a potential barrier is studied in the tem perature region where quantum effects become important. The time evolu tion of the density matrix of a system that deviates initially from eq uilibrium in the vicinity of the barrier top but is in local equilibri um away from the barrier top is determined. Explicit results are given for a range of parameters where the nonequilibrium state is not affec ted by anharmonicities of the barrier potential except for the barrier height. In particular, for a system confined initially to one side of the barrier the relaxation to a quasi-stationary flux state is invest igated. The associated rate constant is evaluated and the relation to other rate formulas is discussed in detail.