State-to-state rate constants for the rotational relaxation of CH(B 2Σ−,v=0,J) in inelastic collisions with Ar

A state-resolved experimental investigation of inelastic collisions of single electronically excited CH(B 2Σ−,v=0,N,Fi) states with Ar is presented by monitoring population distributions in a partly relaxed system. Fluorescence detection of the collision induced population permits spin resolution at low N. Single-collision state-to-state rate constants were determined for low values of N. At the lowest values of N, the most dominant process is spin unit change, F1↔F2, at ΔN=0. The efficiency of the ΔN=0 transitions decreases markedly with increasing N. For ΔN≠0 steps, conservation of the spin label is more important than its change. The very same trends have been recently observed in our laboratory for the fine structure resolved states of CH(A 2Δ,v=0). These results are discussed with respect to propensity rules previously derived and observed for Σ+2 states.