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Description
A fraction of the missing sulfur in dense clouds and circumstellar regions could be in the form of three species not yet detected in the interstellar medium: H_2_S_2_, HS_2_, and S_2_ according to experimental simulations performed under astrophysically relevant conditions. These S-S bonded molecules can be formed by the energetic processing of H_2_S-bearing ice mantles on dust grains, and subsequently desorb to the gas phase. The detection of these species could partially solve the sulfur depletion problem, and would help to improve our knowledge of the poorly known chemistry of sulfur in the interstellar medium. To this purpose we calculated the frequencies and expected intensities of the rotational transitions not previously reported, and performed dedicated ground-based observations toward the low-mass warm core IRAS 16293-2422, a region with one of the highest measured gas-phase H_2_S abundances. Observations in the submillimeter regime were obtained with the APEX 12m telescope during 15h of observation. A total of ~16GHz were covered in a range of about 100GHz, targeting a wide selection of the predicted rotational transitions of the three molecules.
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