Single vibronic level fluorescence spectra of the F band of SO₂

The spectral region of the F band of SO₂ was investigated in crossed supersonic jet and laser beams under conditions of low rotational temperatures. Eight major vibronic bands were identified within the region and their fluorescence spectra were selectively excited and measured. In each spectrum, the relative intensities of the vibrational resonance transitions, particularly for the (n,0,0)″ progressions, were found to change considerably when measured after different time delays following the exciting laser pulse. This indicated efficient collision-induced relaxation processes among the upper vibronic levels, which accounted for the unusual very strong transition into the (1,0,0)″ level. The non-resonance background fluorescence spectrum, which becomes present at the high rovibronic temperatures, was also investigated and discussed in the light of our findings.