  The chemical network governing interstellar sulfur has been the topic of
unrelenting discussion for the past decades due to the conspicuous discrepancy
between its expected and observed abundances in different interstellar
environments. More recently, the astronomical detections of CH3CH2SH and CH2CS
highlighted the importance of interstellar formation routes for sulfur-bearing
organic molecules with two carbon atoms. In this work, we perform a laboratory
investigation of the solid-state chemistry resulting from the interaction
between C2H2 molecules and SH radicals -- both thought to be present in
interstellar icy mantles -- at 10 K. Reflection absorption infrared
spectroscopy and quadrupole mass spectrometry combined with
temperature-programmed desorption experiments are employed as analytical
techniques. We confirm that SH radicals can kick-start a sulfur reaction
network under interstellar cloud conditions and identify at least six
sulfurated products: CH3CH2SH, CH2CHSH, HSCH2CH2SH, H2S2, and tentatively
CH3CHS and CH2CS. Complementarily, we utilize computational calculations to
pinpoint the reaction routes that play a role in the chemical network behind
our experimental results. The main sulfur-bearing organic molecule formed under
our experimental conditions is CH3CH2SH and its formation yield increases with
the ratios of H to other reactants. It serves as a sink to the sulfur budget
within the network, being formed at the expense of the other unsaturated
products. The astrophysical implications of the chemical network proposed here
are discussed.
