Dynamics of Excited Rare-Gas Atoms with Halide Molecules:  The Ar(³P) + ClF → ArCl* + F, ArF* + Cl Reaction

Abstract

The product species originating from the interaction between metastable Ar atoms and the ClF molecules were studied using theoretical (structure and dynamics) methods. Quasiclassical trajectory calculations were carried out on an analytical, monovalued potential energy surface. The energy surface was obtained by means of a fit to CIS (UHF) ab initio points calculated for a set of relevant triatomic configurations, adequately connected to assume that the reaction takes place adiabatically. Cross sections, rate constants, and products' energy disposal for both ArCl* and ArF* excimer formation were calculated, showing a dominancy of the less stable ArCl* + F channel. In addition, angular distributions and rotational alignments for both product channels were analyzed. The influence of reactant internal excitation on integral cross sections and product energy distributions was also studied, considering a wide range of initial rovibrational levels. A remarkable enhancing effect of the reactant rotation was found, as compared to vibration, for the ArCl* product, whereas the opposite trend is observed for the ArF* channel. Whenever possible, the observed behavior was related to both HHL and HLH kinematical considerations. The effect of rotational excitation was used as well to elucidate the angular momentum transfer mechanism among the two competing reaction channels. The role of a relevant rotation-orbiting coupling was identified. Results are found to be, overall, in agreement with the available experimental information, for the title reaction as well as other related systems. This indicates that the fundamental assumption of the present work, namely that the reaction proceeds on a single excited adiabatic potential surface, is accurate enough to account for the main trends of the reaction dynamics.