RESONANCE EMISSION-SPECTROSCOPY OF PREDISSOCIATING SO2 (C)OVER-TILDE(1 B-1(2)) - COUPLING WITH A REPULSIVE (1)A(1) STATE NEAR 200 NM

This work investigates the predissociative (C) over tilde(1 B-1(2)) st ate of SO2 by cooling the SO2 in a pulsed molecular beam and dispersin g the emission upon resonant excitation into several different vibroni c absorption features in the (C) over tilde state between 197 and 212 nm. Unlike at the lower excitation energies, the dispersed emission sp ectra at the higher excitation energies are dominated by progressions with odd quanta in the antisymmetric stretch mode nu(3) and combinatio n bands with up to six quanta in the bending mode nu(2). The formidabl e intensity for emission into vibrational states with odd quanta in th e antisymmetric stretch of the jet-cooled molecule suggests that the i ntermediate state at high energies in the excited state is of mixed el ectronic character at nonsymmetric geometries, so the operative compon ents of the transition moment for excitation and emission may be diffe rent. We discuss our results by considering the avoided crossing seam and coupling between the (C) over tilde(1 B-1(2)) state and two dissoc iative states potentially involved in the electronic predissociation, the 3 (1)A(1) and the 1 (3)A(1) states. (C) 1998 American Institute of Physics. [S0021-9606(98)02037-6].