Detection of benzonitrile in an interstellar cloud helps to constrain interstellar chemistry Interstellar clouds are sites of active organic chemistry (1). Many small, gasphase molecules are found in the dark parts of the clouds that are protected from ultraviolet (UV) photons, but these molecules photodissociate in the external layers of the cloud that are exposed to stellar radiation (see the photo). These irradiated regions are populated by large polycyclic aromatic hydrocarbons (PAHs) with characteristic infrared (IR) emission features. These large aromatics are expected to form from benzene (C6H6), which is, however, difficult to detect because it does not have a permanent dipole moment and can only be detected via its IR absorption transitions against a strong background source (2). On page 202 of this issue, McGuire et al. (3) report the detection of benzonitrile (c-C6H5CN) with radio telescopes. Benzonitrile likely forms in the reaction of CN with benzene; from its observation, it is therefore possible to estimate the abundance of benzene itself.

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检测芳烃的组成部分

在星际云中检测苯甲腈有助于限制星际化学 星际云是活跃有机化学的场所 (1)。许多小的气相分子存在于云的黑暗部分，它们不受紫外线 (UV) 光子的影响，但这些分子在暴露于恒星辐射的云的外层中发生光解（见图）。这些辐照区域充满了具有特征红外 (IR) 发射特征的大型多环芳烃 (PAH)。这些大芳烃预计由苯 (C6H6) 形成，但由于它没有永久偶极矩，因此很难检测到，只能通过其对强背景源的 IR 吸收跃迁来检测 (2)。在本期第 202 页，McGuire 等人。(3) 报道用射电望远镜检测苯甲腈(c-C6H5CN)。CN与苯反应可能生成苯腈；因此，根据观察结果，可以估计苯本身的丰度。