Phosphorescence from indirectly excited 3B1 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 different molecular beam parameters. The spectrum was found to originate from two distinct sets of upper levels which were described in terms of the 1A2 and 3B1 vibrational levels. Collisions of SO2∗Ar type were found to favor 1A2 → 3B1 intersystem crossing and appeared to dominate at high rovibronic temperatures, while SO2∗SO2 collisions favored the reverse intersystem crossing 1A2 ← 3B1. The results also suggest that the reason why the earlier value of the 3B1 → 1A1 phosphorescence quantum yield appeared to increase at low SO2 pressure could be attributed to some collision-induced vibrational transitions that lie in the same spectral region.