VIBRATIONAL-RELAXATION OF NA-2 MOLECULES IN A TRIPLET-STATE - COLLISIONAL TRANSFER FROM A MIXED A(1)SIGMA(-B(3)PI(U) GATEWAY LEVEL TO LONG-LIVED LEVELS OF B(3)PI(U)()(U))

Collision-induced vibrational transitions of Na-2 within the b 3 Pi(1u ) state have been observed in a free jet expansion, using two CW dye l asers for the pump and probe steps. The b-state is entered by the pump laser using a low mixed (A (1) Sigma(u)(+) - b (3) Pi(u)) level as a gateway. The occupations of various upsilon', J'-levels are studied as functions of the position in the flowing gas. The radiative lifetimes of Na-2 in levels which had been populated by vibrational relaxation are found to be very long (> 4 mu s) Cross-sections are estimated for vibrationally inelastic collisions with Na and Ar atoms. (C) 1997 Publ ished by Elsevier Science B.V.