First detection of HS2 in a cold dark cloud

TL;DR

This paper reports the first detection of the sulfur-bearing molecule HS2 in a cold dark cloud, TMC-1, using line survey observations, and explores its formation mechanisms through chemical modeling.

Contribution

It presents the first observation of HS2 in a cold dark cloud and analyzes its abundance and formation pathways, expanding knowledge of sulfur chemistry in space.

Findings

HS2 detected with a column density of 5.7x10^11 cm^-2

HS2 is about seven times more abundant than HSO in TMC-1

Chemical modeling suggests dissociative recombination reactions dominate HS2 formation

Abstract

We report the first detection of HS2 towards the cold dark cloud TMC-1. This is the first observation of a chemical species containing more than one sulphur atom in this type of sources. The astronomical observations are part of QUIJOTE, a line survey of TMC-1 in the Q band (31-50 GHz). The detection is confirmed by the observation of the fine and hyperfine components of two rotational transitions (2(0,2)-1(0,1) and 3(0,3)-2(0,2)). Assuming a rotational temperature of 7 K, we derived an HS2 column density of 5.7x10^11 cm-2, using a local thermodynamic equilibrium model that reproduces the observed spectra. The abundance of HS2 relative to H2 is 5.7x10^-11, which means that it is about seven times more abundant than its oxygenated counterpart HSO. We also explored the main formation and destruction mechanisms of HS2 using a chemical model, which reproduces the observed abundance of HS2 and indicates that dissociative recombination reactions from the ions H2S2+ and H3S2+ play a major role in forming HS2.