Fine-structure state resolved rotationally inelastic collisions of CH(A~2#DELTA#, v=0) with Ar:A combined experimental and theortical study

摘要

A collaborative experimental and theoretical study of rotationally inelastic collisions of CH(A 26. , v = 0) resolved rotational/fine-striIcture levels with argon is presented. Experimental state-to-state .rate constants were extracted from CH A 26. -+ X 2 II fluorescence spectra upon laser excitation to individual levels in the A 26. state in the presence of Ar. Fluorescence detection of the collision-induced population permits resolution of the fine-structure .levels at low N, but no A-doublet discrimination: For the lowest value of N (N=2), the dominant process is the 6.N=O fine-structure-changing transition, and the efficiency of this transition decreases markedly with increasing N. There is ahincrerising preference for conservation of the fine-structure label in 6.N * 0 transitions as N increases. These rate constants have been compared to and interpreted with theoretical rate constants computed through quantum coupled-states calculations of cross sections based on ab initio CH(A 26.)-Ar potential energy surfaces determined by Kaledin and Heaven (to be published). The tendency to conserve the fine-structure label is attributed to the Hund's case (b) nature of the CH(A 26.) state, for which the electron spin is a spectator in the collision.