Time-resolved fluorescence kinetics and 1B1(1Δg) vibronic structure in tunable ultraviolet laser excited SO2 vapor

Abstract

A frequency doubled, tunable dye laser has been used to excite fluorescence from the first excited singlet state of SO₂ (2600–3250 Å). Two different groups of rovibronic states, with different collision‐free lifetimes and bimolecular quenching rates, are observed throughout the region. The major group of states has exceptionally long collision‐free lifetimes (80–600 μsec), which are up to a factor of 20 longer than previously reported. The minor group, which has not been observed by previous workers, has ∼50 μsec lifetimes and a bimolecular quenching rate that is an order of magnitude above the gas kinetic rate. No evidence for collisional equilibration between the groups is found. The exceptionally long lifetimes invalidate the results of previous experiments, from which it was concluded that the first excited singlet state undergoes unimolecular radiationless transitions. The major group is discussed in terms of extensive Renner rovibronic perturbation between an excited, quasilìnear ¹B₁ state and the ground ¹A₁ state. The minor group may result from an overlapping, vibronically induced, ¹A₂←¹A₁ transition.