Agúndez M, Marcelino N, Cernicharo J, Tafalla M
Instituto de Física Fundamental, CSIC, C/ Serrano 123, 28006 Madrid, Spain.
Observatorio Astronómico Nacional (OAN), C/ Alfonso XII 3, 28014 Madrid, Spain.
Astron Astrophys. 2018 Mar 14;611. doi: 10.1051/0004-6361/201832743.
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 7 × 10 cm for HCS and 1.8 × 10 cm for HSC, which translate to fractional abundances relative to H of 2 × 10 and 6 × 10, 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 HCS/HCS abundance ratio is found to be quite low, ~ 1, in contrast with the oxygen analogue case, in which the HCO/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 HCS/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.
我们首次在星际空间中识别出硫甲酰基自由基（HCS）及其亚稳态异构体HSC。借助于用IRAM 30米望远镜在3毫米波段进行的观测，在分子云L483中检测到了这些物种。我们得出HCS的束平均柱密度为7×10厘米，HSC的束平均柱密度为1.8×10厘米，这分别转化为相对于H的分数丰度为2×10和6×10。尽管这些自由基锁定的硫量很低，但它们的检测有助于对暗云中硫的化学性质施加有趣的限制。有趣的是，发现HCS/HCS丰度比相当低，约为1，这与氧类似物的情况形成对比，在暗云中HCO/HCO丰度比约为10。此外，发现自由基HCS比其氧类似物HCO更丰富。HSC的氧类似物亚稳态物种HOC尚未在太空中观测到。这些观测限制与最近关于暗云中硫化学的一个模型的结果进行了对比。该模型至少低估了HCS的分数丰度一个数量级，高估了HCS/HCS丰度比，并且没有提供亚稳态异构体HSC的丰度预测。这些观测结果应该促使对星际云中硫的化学性质进行修正。
