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标题：Detection of interstellar HCS and its metastable isomer HSC: new pieces in the puzzle of sulfur chemistry
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作者：M. Agúndez ; N. Marcelino ; J. Cernicharo 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2018
卷号：611
DOI：10.1051/0004-6361/201832743
语种：English
出版社：EDP Sciences
摘要：We present the first identification in interstellar space of the thioformyl radical (HCS) and its metastable isomer HSC. These species were detected toward the molecular cloud L483 through observations carried out with the IRAM 30 m telescope in theλ3 mm band. We derive beam-averaged column densities of 7 × 1012cm−2for HCS and 1.8 × 1011cm−2for HSC, which translate into fractional abundances relative to H2of 2 × 10−10and 6 × 10−12, respectively. Although the amount of sulfur locked by these radicals is low, their detection allows placing interesting constraints on the chemistry of sulfur in dark clouds. Interestingly, the H2CS/HCS abundance ratio is found to be quite low, ~1, in contrast with the oxygen analog case, in which the H2CO/HCO abundance ratio is around 10 in dark clouds. Moreover, the radical HCS is found to be more abundant than its oxygen analog, HCO. The metastable species HOC, the oxygen analog of HSC, has not yet been observed in space. These observational constraints are compared with the outcome of a recent model of the chemistry of sulfur in dark clouds. The model underestimates the fractional abundance of HCS by at least one order of magnitude, overestimates the H2CS/HCS abundance ratio, and does not provide an abundance prediction for the metastable isomer HSC. These observations should prompt a revision of the chemistry of sulfur in interstellar clouds.
关键词：Key wordsenastrochemistryline: identificationISM: cloudsISM: moleculesradio lines: ISM