Collision Energy Dependence of the Competing Mechanisms of Reaction of Chlorine Atoms with Propene.

Quasi-classical trajectory simulations examine the reaction of Cl with propene across a range of collision energies, from 7 to 28 kJ mol-1. The majority (70% at 7 kJ mol-1, 86% at 14 kJ mol-1, and 93% at 28 kJ mol-1) of reactive trajectories produce HCl by direct abstraction of a hydrogen atom from the methyl group of propene, but the remainder involve a variety of delayed mechanisms. Among these longer-lived trajectories, transient formation of an energized 1-chloropropyl radical intermediate is predominant, with only a minor contribution from the 2-chloropropyl radical and roaming pathways. The branching ratios between these intermediate states are largely invariant to collision energy, although the overall proportion of indirect trajectories increases at lower collision energies. The greater role for longer-lived trajectories is reflected in the computed product scattering angle distributions, which become more isotropic at lower energies. However, the distributions of population over vibrational and rotational states of the product HCl do not change with collision energy because they are controlled by the dynamics late along the reaction path.