Atmospheric Fate of the CHSOO Radical from the CHS + O Equilibrium.

The atmospheric oxidation mechanisms of reduced sulfur compounds are of great importance in the biogeochemical sulfur cycle. The CHS radical represents an important intermediate in these oxidation processes. Under atmospheric conditions, CHS will predominantly react with O to form the peroxy radical CHSOO. The formed CHSOO has two competing unimolecular reaction pathways: isomerization to CHSO, which further decomposes into CH and SO, or a hydrogen shift followed by HO loss, leading to CHS. Previous theoretical calculations have suggested that CHS formation should be the dominant pathway, in disagreement with existing experimental results. Our large active space multireference configuration interaction calculations agree with the experimental results that the formation of CH and SO is the dominant route and the formation of CHS and HO can, at most, be a minor pathway. We support the calculations with new experiments starting from the OH + CHSH reaction for CHS formation under low NO conditions and find a SO yield of 0.86 ± 0.18 within our reaction time of 7.9 s. Model simulations of our experiments show that the SO yield converges to 0.98. This combined theoretical and experimental study thus furthers the understanding of the general oxidation mechanisms of sulfur compounds in the atmosphere.