Long radiative lifetimes of SO2 in a collision-free supersonic molecular beam

Radiative lifetimes and delayed laser-induced fluorescence spectra of cold SO₂ were measured in the range 3000–3150 Å in a differentially pumped collision-free supersonic beam. Lifetimes between 9 and 300 μs were obtained. We show the existence of high-density, low-intensity, and long-lifetime states in the vicinity of the strong spectral transitions.