Reactions of Xe(³P₂) and Xe(³P₁) with HCl, HBr and HI; energy utilization, energy disposal, product rotational polarization and reaction dynamics

Abstract

We report a systematic study of the reactions of Xe(³ P ₁, ³ P ₂) with HCl, HBr and HI using both spectroscopic and molecular beam techniques. No reaction is observed at room temperatures for Xe(³ P ₂) with HCl; analysis of the Xe(³ P ₁)/HCl data yields an estimate of the endoergicity of the ³ P ₂ reaction which agrees within experimental error with the threshold obtained from deconvolution of the excitation function measured in the molecular beam experiments, thus indicating little or no barrier in the entrance channel. Surprisal analysis of the vibrational population distributions obtained by inversion of the rare gas halide spectra yields estimates for the fraction of the available energy disposal into vibration <f _v>. The results are in broad agreement with earlier estimates and are roughly independent of the spin orbit component for a given reaction. Deviations from the purely kinematic limit in the product rotational alignment (<P ₂(Ĵ′ . [kcirc])>) increase across the series HCl, HBr, HI while <f _v> remains moderate, ∼0·5. These results taken with the backward scattering observed for the inelastic channels at low collision energies in the Xe(³ P ₂)/HBr system and the indication of a preferred angle of attack as evidenced by the opacity functions for this system suggest that reaction proceeds via a bent transition state lying towards the product region of the potential energy surface with an important contribution from repulsive release of exoergicity in the exit channel. Similar trends have been observed in the analogous reactions of alkali metal atoms with the hydrogen halides.