Collision-induced angular momentum reorientation and rotational energy transfer in CaF(A 2Π1/2)–Ar thermal collisions

We have carried out an experimental study of collision-induced rotational angular momentum laboratory frame reorientation and energy transfer in CaF(A 2Π1/2, v=0) in thermal collisions with ground state Ar atoms. An optical–optical double resonance (OODR) technique has been used in which the J=1/2, M=+1/2, f-symmetry level of the CaF A 2Π1/2 state is initially populated, from the ground X 2Σ+ electronic state, using circularly polarized cw dye laser radiation at 606 nm. Collision-induced population of nearby magnetic sublevels of the A state, belonging to both e and f symmetry components of J′=1/2 and 3/2, is probed with a second circularly polarized cw dye laser via the E 2Σ+←A 2Π1/2 transition at 560 nm while monitoring subsequent E 2Σ+→X 2Σ+ ultraviolet fluorescence at 290 nm. This experiment has yielded M-dependent thermal rate constants and velocity-averaged cross sections, ratios of which are in partial agreement with those predicted by Alexander and Davis [M. H. Alexander and S. L. Davis, J. Chem. Phys. 79, 227 (1983)] in an infinite-order-sudden, irreducible tensor treatment of the collision dynamics of an open-shell diatomic molecule and a structureless collision partner.