Knowledge Bank

We have studied vibronically resolved fluorescence and phosphorescence spectra of sulfur dioxide vapor (excited by the 297 nm, 302 nm, or 313 nm lines of a mercury/xenon arc) in the pressure range of less than one millitorr to 20 millitorr. Vibrational relaxation effects appear in emission region. At the lowest pressures, emission from the singlet state can be characterized as single vibronic level fluorescence. The strong vibronic bands correspond to progressions in the totally symmetric ground state normal modes. Below 20 millitorr, the relative quantum yield of $SO2$ phosphorescence decreases linearly as the pressure decreases. We will discuss implications of these results with respect to current $data1$ on the kinetics of electronic relaxation in $SO2$ vapor.