Multiphoton-induced fluorescence spectrum of sulfur dioxide

Abstract

The laser-induced fluorescence spectrum of sulfur dioxide (SO2) in the range of 200–460 nm has been obtained with the dyer laser (579 nm) pulsed by an Nd:YAG laser as the excitation source. The transition process, both X1A1→C1B2, excited by three photons and X1A1→A1A2, excited by two photons, has been evaluated. The relaxation kinetics of the excited molecules in the states of C1B2 and A1A2 have been analyzed on the basis of the excitation spectrum in the range of 560–580 nm. The spectral sequence rules are assigned, and it can be calculated that the symmetric stretching vibration and the bending vibration frequencies of the C1B2 state are ω1=942.9 cm−1, ω2=369.8 cm−1, and the bending vibration frequencies of the A1A2 state are ω2=493.4 cm−1. The analysis of the time-resolved spectrum proved that the relaxation process, C1B2→A1A2→X1A1, and the phosphorescent process, a3B1→X1A1, exist simultaneously.