Electronic and Vibrational Relaxation in Sulfur Dioxide Vapor

Abstract

Vibrational relaxation in the A1B1 and a3B1 excited electronic states of sulfur dioxide vapor has been observed by direct spectroscopic means. The effects of vibrational relaxation on the phosphorescence quantum yield have been investigated in the pressure range from 0.6 to 200 mTorr of pure sulfur dioxide and in mixtures of sulfur dioxide with He, N2, CO2, and SF6. Phosphorescence persists at the lowest pressure reached for excitation at 302.0 or 313.1 nm, contrary to previous reports. The mechanism for the production of sulfur dioxide phosphorescence for the wide bandwidth excitation used here (185–370 cm−1) is consistent with recent evidence for two fluorescing species provided by Brus and McDonald from laser-excitation experiments.