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

Hydrogen sulfide (H${}_2$S) is thought to be efficiently formed on grain surfaces through the successive hydrogenation of S atoms. Its non-detection so far in astronomical observations of icy dust mantles thus indicates that effective destruction pathways must play a significant role in its interstellar abundance. While chemical desorption has been shown to remove H${}_2$S very efficiently from the ice, in line with H${}_2$S gas-phase detections, possible solid-state chemistry triggered by the related HS radical have been largely disregarded 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 upon H-atom impact under molecular cloud conditions, providing a comprehensive analysis combined with detailed quantification of both the chemical desorption and ice chemistry that ensues. Experiments are performed in an ultrahigh vacuum chamber at temperatures between 10–16 K. The changes in the solid phase during H-atom bombardment are monitored in situ by means of reflection absorption infrared spectroscopy (RAIRS), and desorbed species are measured with a quadrupole mass spectrometer (QMS). We confirm the formation of H${}_2$S${}_2$ via reactions involving H${}_2$S + H, and quantify its formation cross section under the employed experimental conditions. Additionally, we directly assess the chemical desorption of H${}_2$S by measuring the gas-phase desorption signals with the QMS, providing unambiguous desorption cross sections. Chemical desorption of H${}_2$S${}_2$ was not observed. The relative decrease of H${}_2$S ices by chemical desorption changes from ~85% to ~74% between temperatures of 10 and 16 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 HS radicals at warmer environments. The astronomical implications are further discussed.