Spectroscopic investigation of the G band of SO2

The spectral region of Clementsʹ G band (33150–33400 cm−1) of SO2 was investigated in a crossed supersonic jet and laser beams under low rotational temperature. Ten vibronic origins were identified within the region and their dispersed fluorescence spectra were separately excited and measured. The most intense peak of the G band was found to be composed of two adjacent vibronic bands, separated by only 5 cm−1 and having different Franck-Condon patterns for the (n, 0, 0)″ and (0, m, 0)″ progressions in their dispersed fluorescence spectra. The results were qualitatively interpreted on the basis of a multilevel vibronic coupling between the 1B1 and 1A2 electronic states and were used to explain the observed nonradiative vibronic relaxation.