Identification and Photochemistry of the Mercaptomethyl Radical

Abstract

The mercaptomethyl radical (·CH2SH) is a higher-energy isomer of the methylthio radical (CH3S·) that has been proposed as an important intermediate in atmospheric and interstellar sulfur chemistry. Herein, we report the spectroscopic identification of ·CH2SH during the UV (365 nm) photolysis of CH3S· in a solid Ar-matrix at 10 K. Upon subsequent irradiation at 266 nm, the dehydrogenation of ·CH2SH to yield CS via the intermediacy of the elusive thioformyl radical (HCS·) has also been observed. The characterization of ·CH2SH and HCS· with matrix-isolation IR and UV–vis spectroscopy is supported by 13C-isotope labeling and quantum chemical calculations at the CCSD­(T)-F12a/cc-pVTZ-F12 level using configuration-selective vibrational configuration interaction theory (VCI). The disclosed photochemistry of ·CH2SH provides new insight into understanding the chemical evolution of organosulfur molecules in the interstellar medium (ISM).

Spectroscopic Characterization and Photochemistry of the Atmospherically Relevant Methanesulfenic Acid

“…Concomitantly, H 2 CS···H 2 O, HC­(O)­SH, and H 2 CS were also depleted by formation of the dehydrogenation products CS···H 2 O (3709.3, 3554.9, 1607.8, and 1299.9 cm –1 ), CO/OCS, and CS, respectively. This is consistent with the previously observed photochemistry of HC­(O)­SH (→ CO/H 2 S + OCS/H 2 ) and H 2 CS (→ CS/H 2 ) in Ar-matrices . Notably, the water complex CS···H 2 O was observed before in an Ar-matrix during the photolysis of sulfine (H 2 CSO) at 313 nm .…”

“…However, the photochemistry of CH 3 SOH remains yet unknown. This is in striking contrast to the photochemistry of other sulfur-bearing species CH 3 S·, − CH 3 SH, , and CH 3 SO· − in the atmospheric chemistry of DMS and DMDS. Herein, we report the characterization of CH 3 SOH and its isotopologues CD 3 SOH and 13 CH 3 SOH by using matrix-isolation IR and UV–vis spectroscopy, and its photochemistry has been disclosed.…”