Rotational energy transfer within CH A 2Δ(v=0) and B 2Σ-(v=0) states by collisions with He, Ar, N2, CO, N2O, and CHBr3 using a time-resolved fourier transform spectrometer

By using a step-scan Fourier transform spectrometer, we have studied collisionally-induced rotational energy transfer (RET) of the CH A((2)Delta) (N less than or equal to 16,v = 0) and B((2)Sigma(-)) (N less than or equal to 16,v = 0) states. The collision partners used for the B state are He, Ar, N-2, CO, N2O, and CHBr3, while He and Ar are for the A state. The time-resolved spectra obtained in the nanosecond regime may yield the RET information straightforward under a single pressure of the collider. The resultant RET rate constants for both states range from 10(-12) to 10(-10) cm(3) molecule(-1) s(-1), comparable to the gas kinetic. The trend follows the order of He similar to Ar < N(2)similar to CO < N2O < CHBr3 for the B state, and He < Ar for the A state. For the B state, the findings of multi-quantum changing collisions up to Delta N = +/- 3 and markedly large rate constants imply that the RET collisions are dominated by long-range attractive force. The collision complexes possibly formed between the CH(B) and the colliders are long-lived enough to allow for effective removal of the rotational energy more than a quantum level in a single collision. In contrast, a single quantum change in the RET collision found in the A state suggests dominance of a repulsive interaction between the colliding species, which has been verified previously in the measurements of temperature dependence of the electronic quenching. (C) 2000 American Institute of Physics. [S0021-9606(00)00123-9].