From interstellar carbon monosulfide to methyl mercaptan: paths of least resistance

TL;DR

This study maps the reaction pathways from carbon monosulfide to methyl mercaptan in interstellar ices, providing detailed kinetic data and identifying key intermediates relevant to astrochemical processes.

Contribution

It offers the first comprehensive quantitative analysis of the full H + CS reaction network, including new reaction pathways and kinetic parameters.

Findings

Identified new intermediate species like trans- and cis-HCSH.

Calculated activation and reaction energies for radical-neutral reactions.

Determined branching ratios for barrierless radical-radical reactions.

Abstract

The 29 reactions linking carbon monosulfide (CS) to methyl mercaptan (CH3SH) via ten intermediate radicals and molecules have been characterized with relevance to surface chemistry in cold interstellar ices. More intermediate species than previously considered are found likely to be present in these ices, such as trans- and cis-HCSH. Both activation and reaction energies have been calculated, along with low-temperature (T > 45~K) rate constants for the radical-neutral reactions. For barrierless radical-radical reactions on the other hand, branching ratios have been determined. The combination of these two sets of information provides, for the first time, quantitative information on the full H + CS reaction network. Early on in this network, that is, early on in the lifetime of an interstellar cloud, HCS is the main radical, while later on this becomes first CH2SH and finally CH3S.