Inelastic collision cross section of excited molecules. II. Asymmetries in the cross section for rotational transitions in the Na2(B1Πu) state

Collision-induced rotational energy transfer in electronically excited sodium molecule has been investigated. It has been confirmed that the recently discovered asymmetry in the cross section ( sigma ( Delta j=+1) not= sigma ( Delta J=-1)) exist for most of the vibration-rotational levels in the Na 2 (B 1 Pi u ) state. Levels with rotational quantum numbers from J'=12 to J'=99 in the optically populated B 1 Pi u state have been included. As collision partners all rare gases were used as well as H 2 , HD, D 2 , N 2 and CH 4 . It has been found that the asymmetry in the cross section depends strongly on the nature of the collision partner and that it varies monotonically with the quantum number J' of the Na 2 molecule. Evidence for a temperature dependence of the asymmetry is also given, and some preliminary results on collisional depolarization are deduced. Finally, a semi-classical model is proposed describing the transition process by means of trajectories.