State-to-state rate coefficients for transfer from the rotational levels J=7.5, 20.5, 31.5 and 40.5 in NO(X 2Π1/2, v=2) in collisions with He, Ar and N2 and for J=7.5, 20.5 and 31.5 in collisions with NO:: comparisons between experiment and theory

Using the infrared-ultraviolet double resonance (IRUVDR) technique, state-to-state rate coefficients have been measured for the transfer of NO from the initial rovibronic levels (X (2)Pi(1/2), upsilon = 2 , J(i) = 7.5, 20.5 and 31.5) in collisions with He, Ar, N-2 and NO itself. For relaxation by He, Ar and N-2 from the rotational level J(i) = 40.5, rate coefficients were measured by a new method in which IRUVDR was implemented instantly on NO molecules formed by photodissociation of NO2 at 355 nm. As J(i) is increased the distribution of states (J(f)) was found to change in two ways: (a) the distribution of Delta J(= J(f) - J(i)) values becomes narrower, and (b) negative values of Delta J are increasingly favoured over positive values. Thus > 80% of the transfer from J(i) = 40.5 is to J(f) = 39.5. As with the earlier experimental results for total transfer, the present results for NO-He and NO-Ar collisions are shown to agree quite well with those from coupled states quantum scattering calculations on ab initio potential energy surfaces, although the agreement becomes poorer at high J(i). Possible reasons for this discrepancy are discussed.