Thiols in the ISM: first detection of HC(O)SH and confirmation of C$_2$H$_5$SH

TL;DR

This study reports the first detection of specific thiol compounds in interstellar space, highlighting their potential role in prebiotic chemistry and molecular complexity in the Galactic Centre.

Contribution

First detection of t-HC(O)SH and confirmation of g-C2H5SH in the interstellar medium, expanding knowledge of sulfur-bearing prebiotic molecules.

Findings

Detected t-HC(O)SH with abundance ~1×10^{-10}

Confirmed g-C2H5SH with abundance ~3×10^{-10}

Detected CH3SH with abundance ~5×10^{-9}

Abstract

The chemical compounds carrying the thiol group (-SH) have been considered essential in recent prebiotic studies regarding the polymerization of amino acids. We have searched for this kind of compounds toward the Galactic Centre quiescent cloud G+0.693-0.027. We report the first detection in the interstellar space of the trans-isomer of monothioformic acid (t-HC(O)SH) with an abundance of $\sim\,$1$\,\times\,$10$^{-10}$. Additionally, we provide a solid confirmation of the gauche isomer of ethyl mercaptan (g-C$_2$H$_5$SH) with an abundance of $\sim\,$3$\,\times\,$10$^{-10}$, and we also detect methyl mercaptan (CH$_3$SH) with an abundance of $\sim\,$5$\,\times\,$10$^{-9}$. Abundance ratios were calculated for the three SH-bearing species and their OH-analogues, revealing similar trends between alcohols and thiols with increasing complexity. Possible chemical routes for the interstellar synthesis of t-HC(O)SH, CH$_3$SH and C$_2$H$_5$SH are discussed, as well as the relevance of these compounds in the synthesis of prebiotic proteins in the primitive Earth.