Tests of the extension of variational transition state theory to calculate reaction rates for molecules in selected excited vibrational states

Abstract

Variational transition state theory (VTST) with an adiabatic approximation for excited vibrational modes and semiclassical transmission coefficients to account for tunneling is used to calculate state-specific reaction rates for the collinear reaction H+F2(n=1)→HF+H and the three-dimensional reaction Cl+H2(n=1–4,7)→HCl+H, where n is the initial vibrational quantum number and the rate constants are summed over final vibrational states. We also consider deuterated and tritiated analogs for both reactions for n=1. The results are compared to previous state-selected rate constants calculated without transition state assumptions. Comparisons to accurate quantal results for the H+F2 series test both the semiclassical tunneling methods and the validity of the adiabatic approximation for excited-state dynamical-bottleneck locations. Comparison to quasiclassical trajectory calculations for the Cl+H2 series provide further tests of the adiabatic approximation. In general the VTST/adiabatic-plus-tunneling calculations are quite successful.