Location of energy barriers. VIII. Reagent→product energy conversion on surfaces with sudden or gradual late-barriers

Abstract

At energies well above the threshold for reaction, the effect of additional reagent vibration (ΔV') and relative translation (ΔT') on the product energy distribution (V,R,T,) has been examined on four different substantially endothermic potential-energy surfaces for two extreme mass combinations (LH + H→^endo L + HH and HH + L→^endo H + HL). As noted previously, additional reagent vibration tends to be retained as product vibration, ΔV'→ΔV, and a similar approximate adiabaticity applies to translation, ΔT'→ΔT+ΔR. The present work is concerned with the effect of potential-energy surface and extreme mass-combination on these generalizations. The surfaces examined had late barrier-crests, but surfaces designated S exhibited a sudden rise to the barrier-crest and G a gradual rise. The extent of adiabaticity was found to be significantly greater on the gradual (G-type) surfaces than on the sudden (S-type) ones. The mass-combination LH + H→^endoL + HH (in which enhanced reagent orbital angular momentum correlates with enhanced product rotation) was anomalous in giving ΔT'→ΔR.