Vibrationally Adiabatic Model for the Dynamics of H+H2 Systems

Dynamical calculations are made for the reactions H+H₂, D+D₂, D+H₂, and H+D₂, for linear activated complexes, on the basis of the hypothesis that the zero‐point vibrational energy of the reactant molecule passes smoothly into zero‐point energy for the stretching vibrations of all of the intermediate complexes. By considering vibrations normal to the minimal reaction path, zero‐point energies are calculated at each point along the path. Profiles for $\mathrm{P\hspace{0.17em}+\hspace{0.17em}Z}$ , the sum of the potential and zero‐point energies, show single maxima at the activated state. Dynamical calculations for linear systems show that at high impact energies additional energy is required for crossing the $\mathrm{P\hspace{0.17em}+\hspace{0.17em}Z}$ barrier, arising from the centrifugal effect, but that this energy approaches zero as the impact energy is reduced towards the threshold energy. Free‐energy profiles are constructed for the H+H₂ and D+D₂ systems; at higher temperatures these show double maxima, at each side of the potential‐energy maximum.