Semiclassical variational transition state calculations for the reactions of H and D with thermal and vibrationally excited H₂

We present calculations of the rate constants for the title reactions on a new accurate potential energy surface with a 9.65 kcal mol⁻¹ barrier and a carefully fitted long‐range attraction. The low‐temperature thermal rate constant decreases from the previously calculated value, corresponding to a surface with a barrier of 9.80 kcal mol⁻¹, which is opposite to the direction of change expectedbecause of the change in barrier height. This demonstrates the sensitivity of tunneling contributions to more global characteristics of the surface. The excited‐state (n = 1) rate constants alsochange slightly, but not nearly enough to settle the controversial disagreement of theory with experiment for these rate constants.