A PERIODIC ORBIT APPROACH TO THE SPECTROSCOPY AND DYNAMICS OF SO2(CB2)-B-1-]X(1)A(1)

Dispersed fluorescence spectra of SO2 are simulated by semiclassical m echanics using a spectroscopic potential for the excited state and an empirical and an ab initio surface for the ground electronic state. Th e initial vibrational states on the excited electronic state are calcu lated quantum mechanically, a coherent state representation of which p rovides the initial distributions in the classical calculations. We fi nd two classes of vibrational wavefunction in the upper surface with c haracteristic localization properties, which can be associated with pe riodic orbits emerging from saddle-node bifurcations above the potenti al barrier. The dynamics on the ground surface, induced from the spect roscopic transitions, are analysed with periodic orbits, and the semic lassical Gutzwiller's formula. This type of analysis elucidates the re gularity of the observed spectra.