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

TL;DR

This study combines laboratory experiments and computational methods to explore how carbon disulfide reacts with hydrogen on icy surfaces, revealing pathways to form sulfur compounds relevant to interstellar chemistry.

Contribution

It provides new insights into the hydrogenation mechanisms of CS$_2$ on ice analogues, highlighting quantum tunneling and reaction pathways leading to sulfur-bearing molecules in space.

Findings

CS$_2$ reacts with H via quantum tunneling on icy surfaces.

Formation of H$_2$S, CH$_3$SH, HC(S)SH, and CH$_2$(SH)$_2$ observed.

Reactivity explains non-detection of CS$_2$ in interstellar ices.

Abstract

Carbon disulfide (CS$_2$) 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 CS$_2$ with hydrogen (H) atoms on amorphous solid water (ASW) using laboratory experiments supported by computational calculations. Our results show that CS$_2$ 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 (H$_2$S), methyl mercaptan (CH$_3$SH), and small amounts of dithioformic acid (HC(S)SH) and methanedithiol (CH$_2$(SH)$_2$). The observed reactivity of CS$_2$ with H atoms provides a plausible explanation for the non-detection of CS$_2$ in interstellar ices. Furthermore, the efficient hydrogenation of the complex molecules derived from CS$_2$, namely HC(S)SH and CH$_2$(SH)$_2$, suggests that these species could be easily undergone with H atoms to produce other S-bearing species under ISM conditions.