ACTIVATED RATE-PROCESSES IN MANY DIMENSIONS - ENERGY DIFFUSION WITH SLOW ADJUSTMENT OF A NONREACTIVE MODE

Activated rate processes in two dimensions are studied analytically un der the condition of weak friction on the reactive mode (energy diffus ion) and high friction on the nonreactive coordinate. It is found that the process scenario and, as a consequence, the escape kinetics cruci ally depend on the strength of the mode coupling. When the coupling is strong the energy diffusion does not manifest itself. The kinetics is single-exponential with a rate constant independent of the friction o n the reactive mode. For moderate mode coupling the energy diffusion p lays an important role. Different process scenarios and, hence, the ki netics can be realized depending on the strength of friction on the bo th modes. Both multiexponential decay and single-exponential kinetics are possible. The latter may take place either when particles escape v ia the saddle on the potential surface (the traditional escape scenari o) or when particles escape on a path that avoids the saddlepoint. (C) 1998 Elsevier Science B.V. All rights reserved.