Efficiencies of state and velocity-changing collisions of superthermal CN A²Π with He, Ar, N₂ and O₂

Polarized laser photolysis of ICN is combined with saturated optical pumping to prepare state-selected CN A²? (?' = 4, J = 0.5, F₂, f) with a well-defined anisotropic superthermal speed distribution. The collisional evolution of the prepared state is observed by Doppler-resolved Frequency Modulated (FM) spectroscopy via stimulated emission on the CN A²?-X²S⁺ (4,2) band. The phenomenological rate constants for removal of the prepared state in collisions with He, Ar, N₂ and O₂ are reported. The observed collision cross-sections are consistent with attractive forces contributing significantly for all the colliders with the exception of He. The collisional evolution of the prepared velocity distribution demonstrates that no significant back-transfer into the prepared level occurs, and that any elastic scattering is strongly in the forward hemisphere. © the Owner Societies 2007.