Zero-order ¹B₁(n,0,0) vibrational levels of sulfur dioxide

More than 100 single vibronic level fluorescence spectra of SO₂ throughout the 30400-34230cm^-1 spectral region were selectively excited and recorded in crossed supersonic jet and laser beams under conditions of cold rotational temperatures. It was found that the vibronic origins can be grouped into 5 overlapping regions based on identical Franck-Condon patterns of the X̃¹A₁(n,0,0) progressions. The spacing between the centers of these regions was found to range between 572cm^-1 and 647cm^-1 as opposed to the previously estimated value of 690cm^-1. The onset of the ¹B₁ state in the vibronic coupling was found to be at the 30553cm^-1 band, which is below the previously reported threshold energy by 220cm^-1. The results provide qualitative verification of the multilevel coupling mechanism proposed by Kullmer and Demtröder [Chem. Phys. 92, 423 (1985)].