Thiols in the Interstellar Medium: First Detection of HC(O)SH and Confirmation of C₂H₅SH

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 compound toward the Galactic Center 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 ∼1 × 10−10. Additionally, we provide a solid confirmation of the gauche isomer of ethyl mercaptan (g-C2H5SH) with an abundance of ∼3 × 10−10, and we also detect methyl mercaptan (CH3SH) with an abundance of ∼5 × 10−9. Abundance ratios were calculated for the three SH-bearing species and their OH analogs, revealing similar trends between alcohols and thiols with increasing complexity. Possible chemical routes for the interstellar synthesis of t-HC(O)SH, CH3SH, and C2H5SH are discussed, as well as the relevance of these compounds in the synthesis of prebiotic proteins in the primitive Earth.

Probing the chemical complexity of amines in the ISM: detection of vinylamine (C$_2$H$_3$NH$_2$) and tentative detection of ethylamine (C$_2$H$_5$NH$_2$)

“…As the algorithm did not converge when fitting C 2 H 3 NH 2 with all parameters left free, we fixed the FWHM and V LSR to 18 km s −1 and 67 km s −1 respectively by visual inspection of the most unblended lines. These values are consistent with those from many other molecules previously analysed in G+0.693 (FWHM ∼20 km s −1 , V LSR ∼68 km s −1 ; Requena-Torres et al 2008;Zeng et al 2018;Rivilla et al 2018Rivilla et al , 2019Rivilla et al , 2020Jiménez-Serra et al 2020;Rodríguez-Almeida et al 2021). The resulting LTE fit gives T ex =(18±3) K and N tot =(4.5±0.6)×10 13 cm −2 .…”

“…about a factor >10. This trend has been found for other species such as ethanol (with respect to methanol) or ethyl cyanide (with respect to CH 3 CN; Zeng et al 2018;Rodríguez-Almeida et al 2021). Primary amines are known to be involved in the synthesis of proteinogenic alpha-amino acids Förstel et al (2017).…”

“…To properly evaluate the line contamination by other molecules, over 300 species have been searched for in our dataset. This included not only all the molecules detected towards G+0.693 in previous studies (Requena-Torres et al 2008;Zeng et al 2018;Rivilla et al 2018Rivilla et al , 2019Rivilla et al , 2020Rivilla et al , 2021Jiménez-Serra et al 2020;Rodríguez-Almeida et al 2021), but also those reported in the ISM 5 . The molecule blended 5 See https://cdms.astro.uni-koeln.de/classic/molecules with the transition of C 2 H 3 NH 2 and C 2 H 5 NH 2 is listed in the last column of Table 1.…”

“…We note that the line identification and fitting file used in this analysis is the same as the one used in previous works (e.g. Zeng et al 2018;Rodríguez-Almeida et al 2021) as well as on-going works. Therefore, the excitation temperatures and column densities of blending species are consistent with the ones reported in all these studies.…”

Diastereoselective Formation of trans-HC(O)SH Through Hydrogenation of OCS on Interstellar Dust Grains

“…Sulfur-bearing molecules constitute a fundamental branch of prebiotic chemistry due to the recently gained importance of cysteine C 3 H 7 NO 2 S as a catalyst in the assembly of complex peptides (Foden et al 2020). In cold, interstellar environments, cysteine is far from being detected, but other complex organic molecules (COM) of prebiotic importance bearing S have recently been detected, highlighting ethyl mer-Corresponding author: Germán Molpeceres molpeceres@theochem.uni-stuttgart.de captan C 2 H 5 SH or thioformic acid (HC(O)SH) (Kolesniková et al 2014;Rodríguez-Almeida et al 2021). In turn, the family of compounds to which (HC(O)SH) belongs (thioacids) has also been pointed out as possible catalysts in prebiotic processes in a primordial Earth (Chandru et al 2016).…”