Anharmonic corrections to variational transition state theory calculations of rate constants for a model activated reaction in solution

Abstract

Previous errors in harmonic variational transition state theory calculations of rate constants for a model of an activated reaction in solution are corrected by including anharmonicities in the calculations of bound state energy levels. Harmonic variational transition state theory including multidimensional quantum mechanical corrections for reaction coordinate motion has previously been used to calculate the rate constant for a reaction model corresponding to a single solute coordinate coupled to a harmonic bath. Comparison of these rate constants with accurate quantum mechanical rate constants showed good agreement, in general, with the worst discrepancy to be a factor of 3.6. By including anharmonicities in the bound vibrational potentials to infinite order and calculating the energy levels by a uniform semiclassical prescription, the maximum error is reduced to 42%.