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Hydrogen sulfide (H$_2$S) is thought to be efficiently formed on grainsurfaces through the successive hydrogenation of S atoms. Its non-detection sofar in astronomical observations of icy dust mantles thus indicates thateffective destruction pathways must play a significant role in its interstellarabundance. While chemical desorption has been shown to remove H$_2$S veryefficiently from the ice, in line with H$_2$S gas-phase detections, possiblesolid-state chemistry triggered by the related HS radical have been largelydisregarded so far -- despite it being an essential intermediate in the H$_2$S+ H reaction scheme. We aim to thoroughly investigate the fate of H$_2$S uponH-atom impact under molecular cloud conditions, providing a comprehensiveanalysis combined with detailed quantification of both the chemical desorptionand ice chemistry that ensues. Experiments are performed in an ultrahigh vacuumchamber at temperatures between 10--16 K. The changes in the solid phase duringH-atom bombardment are monitored in situ by means of reflection absorptioninfrared spectroscopy (RAIRS), and desorbed species are measured with aquadrupole mass spectrometer (QMS). We confirm the formation of H$_2$S$_2$ viareactions involving H$_2$S + H, and quantify its formation cross section underthe employed experimental conditions. Additionally, we directly assess thechemical desorption of H$_2$S by measuring the gas-phase desorption signalswith the QMS, providing unambiguous desorption cross sections. Chemicaldesorption of H$_2$S$_2$ was not observed. The relative decrease of H$_2$S icesby chemical desorption changes from ~85% to ~74% between temperatures of 10 and16 K, while the decrease as the result of H$_2$S$_2$ formation is enhanced from~5% to ~26%, suggesting an increasingly relevant sulfur chemistry induced by HSradicals at warmer environments. The astronomical implications are furtherdiscussed.

Interaction of H$_2$S with H atoms on grain surfaces under molecular cloud conditions