Spectroscopic Characterization and Photochemistry of the Atmospherically Relevant Methanesulfenic Acid

Methanesulfenic acid, CH₃SOH, is a fleeting intermediate in the ·OH-initiated oxidation reactions of dimethyl sulfide (DMS) and dimethyl disulfide (DMDS) in the atmosphere. Herein, we report the characterization and photochemistry of CH₃SOH in Ar- and N₂-matrices at 10 K. The characterization of CH₃SOH with matrix-isolation IR and UV-vis spectroscopy is supported by D and ¹³C isotope labeling experiments and quantum chemical calculations. In line with the observed absorption at 260 nm for CH₃SOH, its photolysis at 254 nm leads to dissociation by yielding the novel water complex H₂CS···H₂O, which exhibits a five-membered ring structure with intermolecular S···HO and CH···O hydrogen bonding interactions. Upon further irradiation at 193 nm, the H₂CS···H₂O complex undergoes dehydrogenation to form CS···H₂O, which can further convert to HC(O)SH under irradiation at 254 nm. When the photolysis of CH₃SOH was performed in an O₂-doped Ar-matrix, methanesulfonic acid (MSA, CH₃SO₃H) was obtained as the oxidation product.