Rotational energy transfer in the Na2 b 3Πu state: Propensity rules for rotation, spin–orbit component, and e/f-parity changing collisions

Abstract

State-to-state collision-induced transitions within the Na2 b 3Πu state have been studied by a sub-Doppler optical–optical double resonance (OODR) technique employing cw, single mode dye lasers for the PUMP and PROBE steps. The main experimental results are (1) strong Ω-conservation is observed when a low-J 3Π0 or 3Π1 parent level is initially prepared (we are unable to prepare low-J 3Π2 levels). This Ω-conservation relaxes as J increases. (2) e/f parity conservation (i.e., propensity for even ΔJ changes in homonuclear molecules) is observed at low-J within the 3Π0 manifold. This propensity for e/f-conservation relaxes rapidly as J increases. (3) The e/f parity conservation rule observed within the 3Π0 manifold is observed not to apply to the collision-induced transitions within the 3Π1 manifold. At low-J, ΔJ=±1, e→f transitions are even stronger than ΔJ=±2, e→e transitions. (4) At higher-J, for example J=16, neither Ω-conservation nor e/f-conservation within the 3Π0 manifold are observed. These results are compared with theoretical predictions for a case (a) 3Π state [Alexander and Pouilly, J. Chem. Phys. 79, 1545 (1983)] and with experimental observations on another homonuclear molecule, N2 in the B 3Πg state, which also exhibits intermediate coupling between cases (a) and (b) [Ali and Dagdigian, J. Chem. Phys. 87, 6915 (1987)].