The dynamics of the reaction H+2+H2→H+3+H, with isotopic variations

We performed a merged‐beam study of the reactions HD++D2→HD+2+D, D+3+H, D+2+HD→HD+2+D, D+3+H, in which we measured the absolute reaction cross sections, branching ratios, and product energy distributions over the range of relative kinetic energy from ∼0.002 to 8 eV. Within the experimental uncertainty all three types of data are identical for the two reactant charge states at initial kinetic energies less than 0.5 eV, leading us to believe that adiabatic charge equilibration between the reactants occurs prior to reaction at these low energies. Diabatic behavior becomes increasingly dominanant at higher energies. The reaction mechanism is direct and products are formed with a broad distribution of translational energies. In low energy collisions, on the average, a small fraction of the reaction exothermicity and the reactant excitation energy is converted into translational energy of the products. At higher energies there is a net conversion of translational into internal energy. The reaction energetics ar...