Degenerate four-wave mixing and photofragment yield spectroscopic study of jet-cooled SO2 in the C 1B2 state: Internal conversion followed by dissociation in the X state

The predissociation mechanism of the C̃ state of SO2 have been investigated by the measurements of degenerate four-wave mixing (DFWM), laser-induced fluorescence (LIF) and photofragment yield spectra. The DFWM spectrum of jet-cooled SO2 was measured under a high power condition where the DFWM signal corresponds well to the absorption spectrum. Relative fluorescence quantum yields of various vibronic bands were obtained by comparing the DFWM spectrum with the LIF spectrum. It was found that the fluorescence quantum yields of the vibronic levels involving anti-symmetric stretching (ν3) vibration are considerably smaller than those of other levels. The result indicates that the nonradiative process of the C̃ state is initiated as the internal conversion to the X̃ state and ν3 acts as the promoting mode. By observing the O atom photofragment yield spectrum we confirmed that the predissociation occurs from the (1,4,2) level. Vibronic dependence of the rise time of the O atom generation was found to be in accordance with those of the fluorescence decay rate. The obtained results represent that the dissociation occurs immediately after the internal conversion to the X̃ state.