Accurate reaction rate calculations including internal and rotational motion: A statistical multi-configurational time-dependent Hartree approach

A statistical approach to the direct calculation of thermal rate constants and cumulative reaction probabilities based on flux correlation functions i s presented. It facilitates the accurate treatment of rotational and low fr equency vibrational motion in rate constant calculations. Within this appro ach, a statistical sampling scheme is used to evaluate the trace in the flu x correlation function and the multi-configurational time-dependent Hartree (MCTDH) approach is employed to simulate the system dynamics. The OH+Cl--> O+HCl reaction is studied to demonstrate the efficiency of the approach. Kn own results for vanishing total angular, J=0, are reproduced. Moreover, the rmal rate constants are calculated including all internal and rotational de grees of freedom explicitly, i.e., without invoking a J-shifting or K-conse rving approximation. Based on these results, the accuracy of the J-shifting approximation is discussed. (C) 1999 American Institute of Physics. [S0021 -9606(98)02848-7].