Quasiclassical dynamics of light+heavy–heavy and heavy+heavy–light atom reactions: The reaction X+F2→XF+F(X = Mu, H)

Abstract

The effect of mass variation on the dynamics of exoergic chemical reactions has been investigated using one and three dimensional quasiclassical trajectories. The reactions studied are the light+heavy–heavy atom reactions X+F₂→XF+F(X = Mu, H) and their heavy+heavy–light atom counterparts. For all four reactions, the best extended LEPS potential energy surface No. 2 of Jonathan et al. has been used. Calculations have been performed for the total reaction cross sections, reaction probabilities as a function of impact parameter, product energy disposal, angular distributions, and, for the Mu+F₂ and H+F₂ reactions, rate coefficients and activation energies. It is found that many features of the reactivity of the three dimensional reactions can be understood in terms of the corresponding one dimensional reactions. The reactivity of all four one dimensional reactions in the threshold region is found to be determined by the heights of their vibrationally adiabatic barriers, which occur in the entrance valley, and not by exit valley properties. Comparison with thermal experimental rate coefficients and activation energies for the Mu+F₂ and H+F₂ reactions suggests that tunneling is very important for the Mu reaction, and that a potential surface with a different barrier region topology is probably required in order to account for the experimental results.