A classical-path surface-hopping study of Mu, H and T hot-atom collisions with F2

Abstract

The collision dynamics of processes pertinent to the hot-atom chemistry of the hydrogen isotopes Mu, H and T with F₂ are explored using mixed quantum–classical techniques. We use classical-path surface-hopping and pure classical-path multi-surface trajectory methods with a set of 14 coupled potential energy surfaces (PESs) from a diatomics-in-molecules (DIM) model. We compare with results from the standard quasiclassical trajectory (QCT) method applied to the electronic ground state surface of the same DIM model. We compute reaction- and dissociation cross sections for centre-of-mass collision energies ranging from threshold to 20 eV. In order to quantify the notion of electronic non-adiabaticity we introduce various cross sections measuring electronically non-adiabatic processes. We find that non-adiabatic effects give rise to pronounced changes in the dynamics of the Mu+F₂ system. In particular, collision-induced dissociation of F₂ by Mu is an essentially electronically non-adiabatic process, proceeding efficiently by a mechanism involving transitions to excited repulsive PESs. In contrast, QCT calculations on the electronic ground state surface predict vanishingly small Mu+F₂ dissociation cross sections. We also discuss some consequences of this behaviour for simulations of Mu hot-atom chemistry.