Fluorescence in the dissociative excitation of sulphur dioxide by electron impact

Abstract

Electron-impact excitation of sulphur dioxide at energies > ca. 10 eV results in optical emission from the A3Π and B3Π states of the SO radical. The threshold energy for production of the SO(A3Π) was found to be 10.6 ± 0.5 eV, a value similar to the minimum thermochemical energy requirements. Optical emission excitation functions for the SO(A) state show that in the energy region 10–20 eV an important excitation channel involves the triplet manifold of sulphur dioxide, although there is still a significant contribution from singlet excitation, particularly at higher energies. The SO(A) state is quenched by molecular SO2 with near-unit collisional efficiency, with an estimated rate constant of 8.4 × 10–11 cm3 molecule–1 s–1. Detailed studies on production of SO(B) could not be undertaken owing to considerable spectral interference from molecular sulphur dioxide emission.