Surface Reaction of Methyl Mercaptan (CH₃SH) with Hydrogen Atoms on Amorphous Solid Water

Methyl mercaptan (CH3SH) is one of the S-bearing organic compounds found in the interstellar medium (ISM). In this study, we investigated the surface reactions of solid CH3SH with H atoms on amorphous solid water using experimental and computational methods to examine their physicochemical behavior in the ISM. Consequently, the primary product was discovered to be CH4. As the computational studies show that the dominant reaction pathway is H + CH3SH -> CH3 + H2S, the observed CH4 would result from H addition to CH3. As relatively minor routes, the H abstraction processes from the -CH3 and -SH functional groups of CH3SH, giving rise to CH2SH and CH3S radicals, are confirmed. Although these radicals may form CH3SH again by reactions with H atoms, the loss of CH3SH from the ice surface by chemical desorption would be minor.