An experimental study of the surface formation of methane in interstellar molecular clouds
An experimental study of the surface formation of methane in interstellar molecular clouds
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DOI：
10.1038/s41550-020-1054-y
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发表时间：
2020-04-13
期刊：
影响因子：
14.1
通讯作者：
Linnartz, H.
中科院分区：
文献类型：
--
作者：
Qasim, D.;Fedoseev, G.;Linnartz, H.
甲烷是最简单的稳定分子之一，在空间中既丰富又广泛分布。对低质量和高质量年轻恒星的CH 4冰的观测调查表明，大部分CH 4预计是由尘埃颗粒上的C氢化形成的，并且CH 4冰与固体H2O密切相关。然而，这还没有在受控的实验室条件下进行研究。在这里，我们成功地证明了与C-原子束实施的真空装置中的CH 4冰的形成在两个单独的共沉积实验：C + H在10 K的表面上模仿CH 4的形成之前，直接在尘埃颗粒上形成H2O冰，和C + H + H2O在10 K的表面上模仿CH 4与H2O冰同时形成。我们证实，甲烷可以形成由原子C和H的反应，和甲烷的形成速率是高的两倍时，甲烷是在一个富含水的冰形成。这与观测发现一致，即星际CH 4和H2O在极地冰相中一起形成。导致星际CH 4（和CD 4）冰形成的条件已经被报道，并且可以被纳入天体化学模型，以进一步限制星际介质和其他继承CH 4的区域中的CH 4化学。甲烷冰多年来一直被认为是通过尘埃颗粒上的碳原子连续氢化形成的，但现在Qasim等人已经进行了实验，在有水和没有水的情况下。甲烷在极地冰相中形成得更快。
Methane is one of the simplest stable molecules that is both abundant and widely distributed across space. Observational surveys of CH4 ice towards low- and high-mass young stellar objects showed that much of the CH4 is expected to be formed by the hydrogenation of C on dust grains, and that CH4 ice is strongly correlated with solid H2O. However, this has not been investigated under controlled laboratory conditions. Here, we successfully demonstrate with a C-atom beam implemented in an ultrahigh vacuum apparatus the formation of CH4 ice in two separate co-deposition experiments: C + H on a 10 K surface to mimic CH4 formation directly before H2O ice is formed on the dust grain, and C + H + H2O on a 10 K surface to mimic CH4 formed simultaneously with H2O ice. We confirm that CH4 can be formed by the reaction of atomic C and H, and that the CH4 formation rate is twice as high when CH4 is formed within a H2O-rich ice. This is in agreement with the observational finding that interstellar CH4 and H2O form together in the polar ice phase. The conditions that lead to interstellar CH4 (and CD4) ice formation are reported, and can be incorporated into astrochemical models to further constrain CH4 chemistry in the interstellar medium and in other regions where CH4 is inherited.Methane ice has been presumed to form via the sequential hydrogenation of carbon atoms on dust grains for many years, but now Qasim et al. have performed the experiment, with and without the presence of water. Methane forms more rapidly in the polar ice phase.