Calculation of thermal rate coefficients from the quantum flux autocorrelation function: Converged results and variational quantum transition state theory for O+HD↔OD+H and O+HD↔OH+D

The thermal rate coefficients for the title reactions with zero total angular momentum are calculated by an ℒ² basis-set evaluation of the flux autocorrelation function. We use three dividing surfaces, each one separating one arrangement from the other two. The rate coefficients for O + HD↔OD + H or OH + D are converged to within 1.2% over the temperature range 300-1000 K and to within 2.4% at 200 K. The rate coefficients for the reactions H + OD↔D + OH are converged to within 22% at 1000 K and upper bounds to these rate coefficients are given for the temperature range 200-800 K. Flux autocorrelation functions and rate coefficients are calculated for different positions of the dividing surface to show that the computed rate coefficient is stable with respect to varying this position. Rate coefficients are also calculated by a variational version of quantum mechanical transition state theory and the results are compared to the accurate rate coefficients obtained from flux autocorrelation function theory.