fluorescence from Penning excitation of SO2

Abstract

[Formula: see text] fluorescence emission was observed and analyzed in the 300–550 nm spectral range from a flowing afterglow study of the reaction He(23S) + SO2. The band system, which has its origin at 333.9 nm, is characterized by a long progression of symmetrical stretching vibrations (ν1′, 0, 0) → (ν1″, 0, 0) for 0 ≤ ν1″ ≤ 2 with [Formula: see text] and a number of bending modes (0, 0, 0) → (ν1″, ν2″, 0) for [Formula: see text] with 0 ≤ ν1″ ≤ 9. The symmetrical stretching vibrational frequency of the [Formula: see text] state was determined to be 1264 ± 10 cm−1 which had not been observed previously. The ν2″ bending frequency of the [Formula: see text] state of SO2+ was found to be ~404 cm−1. SO(B3Σ− → X3Σ−) and SO2(Ã1B1 → [Formula: see text]) emission is also observed in the He(23S) + SO2 reaction system, but molecular ion fluorescence is the predominant emission system. From a comparison of the emission spectrum produced by helium metastables with that produced by argon (3P2, 0) metastables, it is concluded that neutral excitation and dissociative excitation occur at large interparticle distances while Penning ionization occurs at small interparticle distances in the case of the sulfur dioxide system.