Interpretation and temperature dependence of the energy of activation for the reactions H + Cl₂, H₂ + I, H + H₂, and isotopic analogs

We compute the Tolman energy of activation for seven collinear reactions using accurate quantum mechanical transition probabilities. The activation energy is generally smaller at lower temperatures, sometimes dramatically so. We also test three kinds of trajectory calculations and find that they are sometimes more accurate for the total energy of activation than for its component parts.