标题： 类地系外行星富氮大气中的氢氰酸 显示英文标题

标题： Hydrogen Cyanide in Nitrogen-Rich Atmospheres of Rocky Exoplanets

摘要： 氢氰酸（HCN）是生命基础分子的关键原料。 在富含氮 (N$_2$) 的大气中形成 HCN 需要首先切断 N$\equiv$N 之间的三重键，然后让原子氮找到一个碳原子。 这两项任务可以通过光化学反应、闪电、撞击或火山活动来实现。 产生大量 HCN 的关键要求是自由的氮 (N$_2$) 和局部的碳氧比 C/O 达到$\geq 1$。 我们讨论了在类地氮 (N$_2$) 含量和地表水库存的岩石系外行星上，通过化学机制生成和破坏 HCN 的过程，并改变主要含碳大气物种的氧化态。 HCN 最容易在富含甲烷（CH$_4$）或乙炔（C$_2$H$_2$）的大气中产生，但也可能在以CO为主的气氛中大量生成（$> 1$ ppm）。甲烷并非生产HCN的必要条件。 我们展示了在CO$_2$-丰富的大气中破坏HCN如何严重依赖于HCN与氧原子反应的能量势垒这一难以确定的因素。 我们讨论了我们的研究结果对于探测光化学产生的HCN、浓缩行星表面的HCN以及其对前生物化学的重要性的影响。 显示英文摘要

摘要： Hydrogen cyanide (HCN) is a key feedstock molecule for the production of life's building blocks. The formation of HCN in an N$_2$-rich atmospheres requires first that the triple bond between N$\equiv$N be severed, and then that the atomic nitrogen find a carbon atom. These two tasks can be accomplished via photochemistry, lightning, impacts, or volcanism. The key requirements for producing appreciable amounts of HCN are the free availability of N$_2$ and a local carbon to oxygen ratio of C/O $\geq 1$. We discuss the chemical mechanisms by which HCN can be formed and destroyed on rocky exoplanets with Earth-like N$_2$ content and surface water inventories, varying the oxidation state of the dominant carbon-containing atmospheric species. HCN is most readily produced in an atmosphere rich in methane (CH$_4$) or acetylene (C$_2$H$_2$), but can also be produced in significant amounts ($> 1$ ppm) within CO-dominated atmospheres. Methane is not necessary for the production of HCN. We show how destruction of HCN in a CO$_2$-rich atmosphere depends critically on the poorly-constrained energetic barrier for the reaction of HCN with atomic oxygen. We discuss the implications of our results for detecting photochemically produced HCN, for concentrating HCN on the planet's surface, and its importance for prebiotic chemistry.