Experimental and computational studies of the hydrogenation of carbon disulfide (CS2) on ice analogues

Carbon disulfide (CS₂) is one of the sulfur-bearing species expected to be present in the interstellar medium (ISM). In this study, we investigated the surface reactions of solid CS₂ with hydrogen (H) atoms on amorphous solid water (ASW) using laboratory experiments supported by computational calculations. Our results show that CS₂ reacts with H atoms through quantum tunneling in the initial step, followed by successive H addition reactions, with or without activation barriers, on icy surfaces. These processes lead to the formation of several sulfur-bearing species, including hydrogen sulfide (H₂S), methyl mercaptan (CH₃SH), and small amounts of dithioformic acid (HC(S)SH) and methanedithiol (CH₂(SH)₂). The observed reactivity of CS₂ with H atoms provides a plausible explanation for the non-detection of CS₂ in interstellar ices. Furthermore, the efficient hydrogenation of the complex molecules derived from CS₂, namely HC(S)SH and CH₂(SH)₂, suggests that these species could be easily undergone with H atoms to produce other S-bearing species under ISM conditions.