SIMBAD references

This work aims to study the unexplained sulfur depletion observed toward dense clouds and protostars. We made simulation experiments of the UV-photoprocessing and sublimation of H₂S and H₂S:H₂O ice in dense clouds and circumstellar regions, using the InterStellar Astrochemistry Chamber (ISAC), a state-of-the-art ultra-high-vacuum setup. The ice was monitored in situ by mid-infrared spectroscopy in transmittance. Temperature-programmed desorption (TPD) of the ice was performed using a quadrupole mass spectrometer (QMS) to detect the volatiles desorbing from the ice. Comparing our laboratory data to infrared observations of protostars we obtained a more accurate upper limit of the abundance of H₂S ice toward these objects. We determined the desorption temperature of H₂S ice, which depends on the initial H₂S:H₂O ratio. UV-photoprocessing of H₂S:H₂O ice led to the formation of several species. Among them, H₂S₂ was found to photodissociate forming S₂ and, by elongation, other species up to S₈, which are refractory at room temperature. A large fraction of the missing sulfur in dense clouds and circumstellar regions could thus be polymeric sulfur residing in dust grains.