Ubiquitous aromatic carbon chemistry at the earliest stages of star formation
Ubiquitous aromatic carbon chemistry at the earliest stages of star formation
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DOI：
10.1038/s41550-020-01253-4
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发表时间：
2021-01-11
期刊：
影响因子：
14.1
通讯作者：
McGuire, Brett A.
中科院分区：
文献类型：
--
作者：
Burkhardt, Andrew M.;Loomis, Ryan A.;McGuire, Brett A.
苯腈（c- c6h5cn，其中“c”表示环状结构）是苯（c- c6h6）的极性替代物，如果能在富含分子的恒星前云TMC-1以外的其他天文来源中发现这种环，则有可能作为一种非常方便的芳香化学射电探针。在这里，我们提出了射电天文学证据，证明在其他四个恒星前，可能是原恒星，来源：Serpens 1A， Serpens 1B， Serpens 2和MC27/L1521F中存在苯腈。这些检测表明，苯腈并不是TMC-1所独有的；相反，芳香化学似乎在恒星形成的最初阶段广泛存在，可能至少持续到原恒星的初始形成。苯腈的丰度远远超过了模型的预测，这些模型可以很好地再现碳链的丰度，如HC7N，一种具有相同重原子的聚氰乙烯，这表明在原始来源中形成平面碳结构（与线性碳结构相反）的化学作用是有利的，但尚未得到很好的理解。相对于碳链分子，苯腈的丰度在金牛座云和蛇蛇云中显示出相当大的差异，这意味着物理条件和云本身的初始元素储存库的重要性。
Benzonitrile (c-C6H5CN, where 'c' indicates a cyclic structure), a polar proxy for benzene (c-C6H6), has the potential to serve as a highly convenient radio probe for aromatic chemistry, provided that this ring can be found in other astronomical sources beyond the molecule-rich prestellar cloud TMC-1. Here we present radio astronomical evidence of benzonitrile in four other prestellar, and possibly protostellar, sources: Serpens 1A, Serpens 1B, Serpens 2 and MC27/L1521F. These detections establish that benzonitrile is not unique to TMC-1; rather, aromatic chemistry appears to be widespread throughout the earliest stages of star formation, probably persisting at least until the initial formation of a protostar. The abundance of benzonitrile far exceeds predictions from models that well reproduce the abundances of carbon chains such as HC7N, a cyanpolyyne with the same heavy atoms, indicating that the chemistry responsible for planar carbon structures (as opposed to linear ones) in primordial sources is favourable but not well understood. The abundance of benzonitrile relative to carbon chain molecules displays sizable variations between sources within the Taurus and Serpens clouds, implying the importance of physical conditions and initial elemental reservoirs of the clouds themselves.