Spectroscopic and Kinetic Studies of the ClSO Radical from Cl2SO Photolysis

• Published in: Journal of the American Chemical Society 2022-11, Vol.144 (44), p.20323-20331
• Main Authors: Chao, Wen, Jones, Gregory H., Okumura, Mitchio, Percival, Carl J., Winiberg, Frank A. F.
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/jacs.2c07912

Thionyl chloride (Cl2SO) serves as a common Cl atom source in widespread applications of chlorine chemistry though little is known about the reactivity and spectroscopy of the ClSO radical after a Cl–S bond cleavage. We performed a Pulsed Laser Photolysis experiment to detect ClSO from Cl2SO photolysis at 248 nm in a gas-flow reactor by time-resolved UV–vis transient absorption spectroscopy. A few chemical tests, using I2 and NO2, suggested the structured absorption band between 260 and 320 nm belonged to ClSO radical and that the termolecular ClSO + Cl + M → Cl2SO association reaction occurred. From EOMIP-CCSD/ano-pVQZ calculations, the ClSO band was assigned to the 12A″ ← X2A″ transition involving the π* ← π transition of the SO bond and the vibrational progression to the SO stretching mode of the 12A″ state, with a maximum cross-section = (2.0 ± 0.5) × 10–18 cm2 near 286 nm (1σ uncertainty) and an average spacing of vibrational structure of 658 cm–1. The rapid decay of the ClSO signal monitored near 303 nm could be fit to a second-order kinetic model over 10–90 Torr, which yields an effective bimolecular rate coefficient k Cl+ClSO = (1.48 ± 0.42) × 10–11 cm3 molecule–1 s–1 at 292 K and 90 Torr (1σ uncertainty). This fast recombination reaction suggests that Cl-containing SO x species might act as significant Cl atom reservoirs in sulfur oxide-rich environments such as Venus’ atmosphere. Moreover, the reported UV spectrum provides a new means for monitoring the ClSO radicals.