Detection of monothioformic acid towards the solar-type protostar IRAS 16293–2422

Abstract

In the interstellar medium (ISM), the complex organic molecules that contain the thiol group (–SH) play an important role in the polymerization of amino acids. We look for SH-bearing molecules in the chemically rich solar-type protostar IRAS 16293–2422. After extensive spectral analysis using the local thermodynamic equilibrium (LTE) model, we have detected the rotational emission lines of trans-isomer monothioformic acid (t-HC(O)SH) towards the IRAS 16293 B using the Atacama Large Millimeter/Submillimeter Array (ALMA). We did not observe any evidence of cis-isomer monothioformic acid (c-HC(O)SH) towards the IRAS 16293 B. The column density of t-HC(O)SH towards the IRAS 16293 B was (\(1.02\pm 0.6)\times 10^{15}~\hbox {cm}^{-2}\) with an excitation temperature of \(125\pm 15\) K. The fractional abundance of t-HC(O)SH with respect to \(\hbox {H}_{2}\) towards the IRAS 16293 B is \(8.50\times 10^{-11}\). The column density ratio of t-HC(O)SH/\(\hbox {CH}_{3}\hbox {SH}\) towards the IRAS 16293 B is 0.185. We compare our estimated abundance of t-HC(O)SH towards the IRAS 16293 B with the abundance of t-HC(O)SH towards the galactic center quiescent cloud G\(+\)0.693–0.027 and hot molecular core G31.41\(+\)0.31. After the comparison, we found that the abundance of t-HC(O)SH towards the IRAS 16293 B is several times of magnitude lower than G\(+\)0.693–0.027 and G31.41\(+\)0.31. We also discussed the possible formation mechanism of t-HC(O)SH in the ISM.