STIFFNESS EFFECTS IN MULTIDIMENSIONAL DIFFUSIVE BARRIER CROSSING

The model of Agmon and Kosloff for two-dimensional diffusive barrier crossing is extended. We demonstrate how an increase in stiffness of the potential perpendicular to the reaction coordinate leads to viscosity dependent rates which are closer to the one-dimensional Kramers results. The range over which the dynamics are truly two dimensional is characterized by a fractional viscosity dependence of reaction rates and viscosity dependent activation energies. It is a transition region between Kramers behaviors observed in the two extreme limits. A simple kinetic approximation rationalizes these observations as arising from two competing pathways. It shows surprisingly good agreement with the full calculation.