Classical Dynamics of the Reaction of Fluorine Atoms with Hydrogen Molecules. III. The Hot-Atom Reactions of 18F with HD

Abstract

Excitation functions for the various product channels in reactions of hot 18F atoms with ground-state HD are calculated using the Monte Carlo quasiclassical trajectory technique and an optimized semi-empirical potential energy surface. The production of H18F and D18F and dissociation into F+H+D18 are reported as a function of the center-of-mass collision energy over the range 0.1–65.0 eV. The calculated excitation functions for H18F and D18F cross at ∼ 7 eV indicating an inversion in the intramolecular isotope effect with increasing collision energy. Features of these excitation functions and the calculated product energy distributions are discussed in terms of simple mechanistic models. The trajectory results, on the average, correlate well with the predictions of the spectator stripping model from epithermal collision energies up to the limiting energy where this model would lead only to dissociation. The high-energy tail of the abstraction excitation functions, however, is shown to be attributable to a mechanism which is the antithesis of spectator stripping. In these high-energy collisions, the nearer atom of the HD collides violently with the fluorine atom and recoils away. The training ``abandoned atom'' is left behind in the vicinity of the fluorine atom, with which it subsequently reacts. Information about a computer-animated film of trajectories selected from those calculated in this work illustrating these mechanistic interpretations will be supplied on request.