Vibrational relaxation of Na2 molecules in a triplet state: collisional transfer from a mixed A 1Σu+ − b 3Πu gateway level to long-lived levels of b 3 Πu

Collision-induced vibrational transitions of Na2 within the b 3Π1u state have been observed in a free jet expansion, using two CW dye lasers for the pump and probe steps. The b-state is entered by the pump laser using a low mixed (A 1Σu+ − b 3Πu) level as a gateway. The occupations of various v′,J′-levels are studied as functions of the position in the flowing gas. The radiative lifetimes of Na2 in levels which had been populated by vibrational relaxation are found to be very long (> 4 μs). Cross-sections are estimated for vibrationally inelastic collisions with Na and Ar atoms.