Experiments on collisional relaxation of Na2 molecules in the b 3Πu state

Rotationally inelastic collisions in the b 3Πu state of Na2 are observed in a free jet expansion by means of two-step laser excitation, using a mixed singlet-triplet level as a gateway. The evolution of the occupation of collisionally populated levels and of the primary excited level are studied as functions of the downstream distance, yielding the effective lifetimes of these levels. Possibilities are discussed to produce molecules in long-lived levels of the b 3Πu state by means of rovibrational relaxation in such a free-jet apparatus.