PHOSPHORESCENCE FROM INDIRECTLY EXCITED B-3(1) VIBRATIONAL LEVELS OF JET-COOLED SO2

A supersonic jet of SO2, seeded in Ar, was crossed with a 301.9-304.3 nm tilted laser beam and the resulting luminescence spectrum from the collisionally populated low SO2 vibronic levels was measured under dif ferent molecular beam parameters. The spectrum was found to originate from two distinct sets of upper levels which were described in terms o i the (1)A(2) and B-3(1) vibrational levels. Collisions of SO2-Ar typ e were found to favor (1)A(2) --> B-3(1) intersystem crossing and appe ared to dominate at high rovibronic temperatures, while SO2-SO2 colli sions favored the reverse intersystem crossing (1)A(2) <-- B-3(1). The results also suggest that the reason why the earlier value of the B-3 (1) --> (1)A(1) phosphorescence quantum yield appeared to increase at low SO, pressure could be attributed to some collision-induced vibrati onal transitions that lie in the same spectral region.