Comparison of variational transition state theory and quantum sudden calculations of three-dimensional rate coefficients for the reactions D(H)+BrH → DBr(HBr)+H

We calculate rate coefficients for the three-dimensional reactions H+BrH→HBr+H and D+BrH→DBr+H using two different dynamical methods but with the same potential energy surface. One method is a three-dimensional quantum mechanical technique in which the energy sudden approximation is used for the entrance reaction channel and the centrifugal sudden approximation is applied to the exit reaction channel. The second method is improved canonical variational transition state theory with small-curvature-tunneling semiclassical adiabatic ground-state transmission coefficients. The potential energy surface is an empirically adjusted diatomics-in-molecules surface which has a very narrow barrier to reaction. The rate coefficients predicted by the two very different dynamical theories are in excellent agreement-they differ by less than 20% over the temperature range from 150 to 500 K.