Publication Date:
2014-07-12
Description:
In a recent article, we reported the UV irradiation of H 2 S:H 2 O ice and estimated upper limits for solid H 2 S in protostars. Photoproducts of H 2 S ice processing were proposed as a plausible explanation of sulphur depletion towards dense clouds and protostars. But the photochemistry of H 2 S with C-bearing molecules like CO and CH 3 OH was not explored. We simulate experimentally the formation of organic products made from UV irradiation and warm-up of CO or CH 3 OH ice containing H 2 S. Our experiments were performed under ultrahigh vacuum conditions using the Interstellar Astrochemistry Chamber. We used infrared spectroscopy and quadrupole mass spectrometry to monitor the solid and gas phase simultaneously during the experiments. The main species produced after irradiation of H 2 S:CO ice mixtures were H 2 S 2 , HS $_2^\cdot$ , CS 2 , H 2 CO, and OCS. In H 2 S:CH 3 OH irradiation experiments CO, CO 2 , CH 4 , H 2 CO, and CS 2 were formed. A complex organic refractory residue remained at room temperature. This experimental evidence supports that dust grains are likely a reservoir of the missing sulphur in dense clouds and circumstellar regions. Indeed, with the exception of CS 2 and OCS, we found that most of the sulphur contained in refractory photoproducts that were stable at room temperature is likely in the form of S-chains. Our results are used to interpret the observations of OCS and CS 2 in different astrophysical environments.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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