Resonance emission spectroscopy of predissociating SO2 C(11B2): Coupling with a repulsive 1A1 state near 200 nm

This work investigates the predissociative C(11B2) state of SO2 by cooling the SO2 in a pulsed molecular beam and dispersing the emission upon resonant excitation into several different vibronic absorption features in the C state between 197 and 212 nm. Unlike at the lower excitation energies, the dispersed emission spectra at the higher excitation energies are dominated by progressions with odd quanta in the antisymmetric stretch mode ν3 and combination bands with up to six quanta in the bending mode ν2. The formidable intensity for emission into vibrational states with odd quanta in the antisymmetric stretch of the jet-cooled molecule suggests that the intermediate state at high energies in the excited state is of mixed electronic character at nonsymmetric geometries, so the operative components of the transition moment for excitation and emission may be different. We discuss our results by considering the avoided crossing seam and coupling between the C(11B2) state and two dissociative states potentially involved in the electronic predissociation, the 31A1 and the 13A1 states. copyright 1998 American Institute of Physics