分子云中含氮复杂有机分子的形成：通过C$_2$H$_2$冰的紫外光解生成乙烯亚胺、乙腈、乙醛亚胺和乙烯胺
Formation of N-bearing complex organic molecules in molecular clouds: Ketenimine, acetonitrile, acetaldimine, and vinylamine via the UV photolysis of C$_2$H$_2$ ice
AI总结：
本研究通过10 K下C$_2$H$_2$:NH$_3$冰的紫外光解实验，揭示含氮COM的生成路径与转化关系，并给出有效截面。
摘要：
星际富H$_2$O冰中的固态C$_2$H$_2$化学反应已被提出，用于解释在早期恒星形成区域中天文观测到的复杂有机分子（COMs），包括乙烯酮（CH$_2$CO）、乙醛（CH$_3$CHO）和乙醇（CH$_3$CH$_2$OH）。近期针对C$_2$H$_2$+OH/H反应的实验室研究和理论计算支持了这一形成机制。然而，形成含氮物种的类似反应C$_2$H$_2$+NH$_2$被认为具有相对较低的速率常数，比C$_2$H$_2$+OH的数值低数个数量级。本工作将我们此前关于含氧COM形成的实验室研究加以扩展，在分子云条件下研究由宇宙射线诱导的次级紫外光子触发的C$_2$H$_2$与NH$_3$冰之间的相互作用。实验在超高真空腔中进行，以研究10 K下C$_2$H$_2$:NH$_3$冰混合物的紫外光解。所研究的C$_2$H$_2$与NH$_3$紫外光解离产生的NH$_2$自由基和H原子的冰化学过程，导致形成若干含氮COM，包括乙烯胺（CH$_2$CHNH$_2$）、乙醛亚胺（CH$_3$CHNH）、乙腈（CH$_3$CN）、乙烯亚胺（CH$_2$CNH），以及暂定的乙胺（CH$_3$CH$_2$NH$_2$）。实验结果表明，CH$_2$CHNH$_2$作为第一代产物立即且大量生成，并进一步转化为其他化学衍生物。文中推导了母体物种和COM的有效破坏与形成截面值，并讨论了这些分子之间的化学联系及其天文相关性。
英文摘要：
The solid-state C$_2$H$_2$ chemistry in interstellar H$_2$O-rich ice has been proposed to explain astronomically observed complex organic molecules (COMs), including ketene (CH$_2$CO), acetaldehyde (CH$_3$CHO), and ethanol (CH$_3$CH$_2$OH), toward early star-forming regions. This formation mechanism is supported by recent laboratory studies and theoretical calculations for the reactions of C$_2$H$_2$+OH/H. However, the analog reaction of C$_2$H$_2$+NH$_2$ forming N-bearing species has been suggested to have a relatively low rate constant that is orders of magnitude lower than the value of C$_2$H$_2$+OH. This work extends our previous laboratory studies on O-bearing COM formation to investigate the interactions between C$_2$H$_2$ and NH$_3$ ice triggered by cosmic ray-induced secondary UV photons under molecular cloud conditions. Experiments were performed in an ultra-high vacuum chamber to investigate the UV photolysis of the C$_2$H$_2$:NH$_3$ ice mixture at 10 K. The studied ice chemistry of C$_2$H$_2$ with NH$_2$ radicals and H atoms resulting from the UV photodissociation of NH$_3$ leads to the formation of several N-bearing COMs, including vinylamine (CH$_2$CHNH$_2$), acetaldimine (CH$_3$CHNH), acetonitrile (CH$_3$CN), ketenimine (CH$_2$CNH), and tentatively ethylamine (CH$_3$CH$_2$NH$_2$). The experimental results show an immediate and abundant CH$_2$CHNH$_2$ yield as the first-generation product, which is further converted into other chemical derivatives. The effective destruction and formation cross-section values of parent species and COMs were derived, and we discuss the chemical links among these molecules and their astronomical relevance.
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