Rotational-state resolved coupling of CH A (2)Delta and B (2)Sigma(-) in collisions with CO2

Inelastic collisions of selected rovibronic levels of the CH A(2)Delta and B(2)Sigma (-) states with CO2 have been investigated experimentally. Initia l levels in A(2)Delta, v = 1 and B(2)Sigma (-), v = 0 were prepared by sele ctive laser excitation. Time-gated emission from the initial and product le vels was dispersed at rotational resolution for the first time. Conditions were established where 60-80% of the population remained in the initially p opulated rovibronic level. The rotational state propensities were establish ed for electronically inelastic collisional transfer from A(2)Delta, v = 1 to B(2)Sigma (-), v = 0. The reverse transfer is complicated by the spectra l overlap of the A-X(1,1) and (0,0) bands. A high N' component can unambigu ously be assigned to A(2)Delta, v = 0. The distributions of DeltaN for inte r-electronic state transfer are generally broader than for pure rotational energy transfer within either state, particularly at higher N where the res ults are more clear-cut. For these levels the redistribution of rotational population during electronic transfer is, however, less complete than impli ed by a statistical prior distribution. This suggests that the electronic s tate-changing collisions sample more strongly interacting regions of the CH . . . CO2 excited state potentials than are required to cause pure rotatio nal relaxation. These interactions are not sufficiently strong, however, to promote complete rotational (or vibrational) energy redistribution during the collision.