Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p.153j&link_type=abstract
The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole
Astronomy and Astrophysics
Astronomy
Scientific paper
Sulfur is highly depleted in the gas phase toward dense clouds and circumstellar regions and might therefore be present in dust grains in those environments. The chemistry of S-bearing species at cryogenic temperatures is poorly known. So far, OCS was the only S-species detected in ice mantles, thanks to its high band strength value in the infrared. H2S should a priori be the most abundant S-product under the reducing ice matrix conditions. We studied experimentally the photochemistry of H2S-bearing ice induced by vacuum UV photons, using ISAC, a state-of-the-art ultra-high-vacuum setup, to gain knowledge on the chemistry of sulfur species and clarify the depletion of sulfur in dense clouds and circumstellar regions. The mid-infrared spectra of H2S ice at various temperatures, as pure ice or mixed with H2O and CO were measured. Temperature programmed desorption (TPD) of the ice was performed, using a quadrupole mass spectrometer (QMS) to detect the volatiles desorbing from the ice. In H2S:CO ice the desorption of H2S occurs at the same temperature as for pure H2S ice, around 82 K. In a water ice matrix, the desorption temperature of H2S depends on the initial H2S:H2O ratio and the heating rate, while a fraction of the H2S co-desorbs with H2O. UV-photoprocessing of H2S leads to the formation of H2S2, which can photodissociate forming S2. Sulfur polymerization results from photoprocessing of H2S, forming S8 very efficiently. Furthermore, UV-photoprocessing of H2S in a CO matrix leads to the formation of CO2 and H2CO as the principal components, in addition to different S-bearing species that remain in solid phase at higher temperatures. These experimental results support that the refractory products of H2S ice processing could explain the missing sulfur in dense clouds and circumstellar regions.
Jiménez-Escobar A.
Muñoz Caro Guillermo Manuel
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