Generalized transition state theory and least-action tunneling calculations for the reaction rates of H(D) + H₂(n=1) → H₂(HD) + H

We report improved canonical variational theory calculations with least-action transmission coefficients for the reactions H + H₂(n=1) and D + H₂(n=1), where n denotes the vibrational quantum number, in both collinear and three-dimensional worlds and for three different potential surfaces. Where possible we compare to accurate or more complete quantal calculations and find very good agreement. For the three-dimensional reaction and the most accurate available potential energy surfaces we compare to all available experimental determinations at 297-356 K; the experimental results are larger than the calculated rate constants by factors of (in chronological order) 26, 17, 60, 5, and 8. The disagreement is probably due in large part to the difficulty of experiments.