RATE THEORY AND QUANTUM ENERGY-FLOW IN MOLECULES - MODELING THE EFFECTS OF ANISOTROPIC DIFFUSION AND OF DEPHASING

We examine the effect on energy flow and unimolecular dissociation of anisotropic diffusion in quantum number space and dephasing, using a s caling approach to describe the energy flow and localization. This app roach can be applied to systems with local couplings in the quantum nu mber space of approximate normal modes. We find that anisotropy in the coefficient of diffusion on the constant energy surface can combine w ith anistropy in the finite extent of state space to produce results w hich mimic those of a lower dimensional isotropic system, due to the e arly saturation of rapidly relaxing modes. We discuss the diffusion wh ich is caused by dephasing, for both delocalized and localized systems . The results for the energy flow dynamics are used to find correction s to the RRKM reaction rate caused by returns to the region of reactiv e states. We find that returns are enhanced near the transition to loc alized eigenstates, causing a greatly diminished average reaction rate . However, we also find that dephasing can cause the average reaction rate to increase over the value for an isolated system.