Experimental and theoretical study of Lambda-doublet resolved rotationallyinelastic collisions of highly rotationally excited CH(A (2)Delta,v=0) with Ar

A collaborative experimental and theoretical study of rotationally inelasti c collisions of resolved CH(A (2)Delta ,v=0) Lambda -doublet levels of high rotational angular momentum N with argon is presented. Experimental state- to-state rate constants were extracted from CH A (2)Delta -->X (2)Pi resolv ed fluorescence spectra upon laser excitation to individual levels in the A (2)Delta state in the presence of Ar. Fluorescence detection of the collis ion-induced final-state populations permits resolution of the Lambda -doubl et levels at high N, but without fine-structure discrimination. The largest rate constants were for DeltaN=0 A'<---->A" symmetry-changing transitions. For exothermic DeltaN <0 transitions, the rate constants decreased monoton ically with increasing magnitude of DeltaN, and a slight preference for con servation of the Lambda -doublet symmetry was found. These rate constants h ave been compared and interpreted with theoretical rate constants computed through quantum coupled-states calculations of cross sections based on ab i nitio CH(A (2)Delta)-Ar potential-energy surfaces determined by G. Kerenska ya, A. Kaledin, and M. C. Heaven (to be published). The electronic symmetry of the rotational, fine-structure/Lambda -doublet levels of a (2)Delta ele ctronic state has also been analyzed. (C) 2001 American Institute of Physic s.