星际HCS及其亚稳异构体HSC的探测：硫化学难题中的新部分
Detection of interstellar HCS and its metastable isomer HSC: new pieces in the puzzle of sulfur chemistry
摘要：
我们首次在星际空间中发现了硫代甲酰基自由基（HCS）及其亚稳异构体HSC。这些物质是在分子云L483附近被探测到的，这要归功于IRAM 30米望远镜在3毫米波段的观测。我们推导出7 e12 cm-2的HCS和1.8e11 cm-2的HSC，这转化为相对于H2的2 e-10和6 e-12，分别的分数丰度的光束平均柱密度。虽然这些自由基锁定的硫含量很低，但它们的检测可以对乌云中硫的化学性质提出有趣的限制。有趣的是，发现H2 CS/HCS丰度比相当低，约为1，与氧气类似物的情况下，其中H2 CO/HCO丰度比在乌云中约为10。此外，自由基HCS被发现比其氧类似物HCO更丰富。HSC的氧类似物亚稳物种HOC尚未在太空中观察到。这些观测限制面临的结果，最近的模型的化学硫在乌云。该模型低估了至少一个数量级的HCS的丰度分数，高估了H2 CS/HCS的丰度比，并没有提供一个亚稳异构体HSC的丰度预测。这些观测结果应该会促使人们对星际云中硫的化学性质进行修正。
英文摘要：
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 thanks to observations carried out with the IRAM 30m telescope in the 3 mm band. We derive beam-averaged column densities of 7e12 cm-2 for HCS and 1.8e11 cm-2 for HSC, which translate to fractional abundances relative to H2 of 2e-10 and 6e-12, respectively. Although the amount of sulfur locked by these radicals is low, their detection allows to put interesting constraints on the chemistry of sulfur in dark clouds. Interestingly, the H2CS/HCS abundance ratio is found to be quite low, around 1, in contrast with the oxygen analogue 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 analogue, HCO. The metastable species HOC, the oxygen analogue of HSC, has not been yet observed in space. These observational constraints are confronted 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.
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