Vibrational enhancement of the reaction rate and steric requirements in the H + D₂(ν) and D + H₂(χ) reactions

The cone of acceptance for H + H₂ reactive collisions is shown to open up upon stretching of the H₂ bond. At a given translational energy, the steric factor is thus much larger for vibrationally excited reagents as demonstrated by classical trajectory computations for H + D₂(ν) and D + H₂(ν). At a given total energy, the efficacy of reagent vibrational excitation is conveniently represented by a surprisal plot. The surprisal parameter is essentially isotopically invariant.