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

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Abstract
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. 7 9, 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.