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

A state-resolved experimental investigation of inelastic collisions of sing le electronically excited CH(B (2)Sigma (-),v=0,N,F-i) states with Ar is pr esented by monitoring population distributions in a partly relaxed system. Fluorescence detection of the collision induced population permits spin res olution at low N. Single-collision state-to-state rate constants were deter mined for low values of N. At the lowest values of N, the most dominant pro cess is spin unit change, F-1<---->F-2, at DeltaN=0. The efficiency of the DeltaN=0 transitions decreases markedly with increasing N. For DeltaN not e qual0 steps, conservation of the spin label is more important than its chan ge. The very same trends have been recently observed in our laboratory for the fine structure resolved states of CH(A (2)Delta ,v=0). These results ar e discussed with respect to propensity rules previously derived and observe d for (2)Sigma (+) states. (C) 2001 American Institute of Physics.