论文标题
HCN生产在Hadean地球大气中的实验和理论研究
An experimental and theoretical investigation of HCN production in the Hadean Earth atmosphere
论文作者
论文摘要
地球生命起源的一个关键早期阶段可能涉及在减少的，主要是H $ _2 $大气中生产氰化氢（HCN）。 HCN对生命的起源至关重要，因为它可能是几种构成RNA和蛋白质（包括核苷酸酶，核苷酸，氨基酸和核糖）的生物分子的先兆。在这项工作中，我们对减少大气条件下的HCN产生（89-95％H $ _2 $）进行了深入的实验和理论研究，可能代表了Hadean Eon的最早阶段，约4.5-43亿年前。我们利用冷等离子体排放（一种对短波紫外线辐射的实验室类似物）来模拟大气上层的HCN产生，以$ _4 $的丰度在0.1-6.5％之间。然后，我们将实验质谱测量与我们的理论等离子体模型相结合，以估计实验中产生的HCN浓度。我们发现，上层大气中的HCN生产与CH $ _4 $丰度线性缩放，并且关系[HCN] = 0.13 $ \ pm $ 0.01 [CH $ _4 $]。 HCN的浓度预计将低约2-3个数量级。在我们的实验中添加1％的水导致HCN产生降低了约50％。我们发现我们的实验中主要负责HCN的四个反应：（i）$^4 $ n + ch $ _3 $ - > h $ _2 $ _2 $ _2 $ cn + h-> hcn + hcn + h $ _2 $，（ii）$^4 $ n $ n + ch-> cn + cn + cn + cn + ch $ _4 $ _4 $ - > hcn + ch $ _4 $ _3 $ _42 $^4 $ n-> hcn + ch $ _3 $，以及（iv）$^4 $ n + $^3 $ ch $ _2 $ - > hcn + H.最有利的野生动物的hadean氛围在CH $ _4 $（> 5％）中非常丰富，并且由于绿屋的影响很可能很热。在这种益生元的情况下，将HCN纳入有机危险中可能很重要，后来可以将生物分子和前体释放到第一个池塘中。
A critical early stage for the origin of life on Earth may have involved the production of hydrogen cyanide (HCN) in a reducing, predominantly H$_2$ atmosphere. HCN is crucial for the origin of life as it is a possible precursor to several biomolecules that make up RNA and proteins including nucleobases, nucleotides, amino acids, and ribose. In this work, we perform an in depth experimental and theoretical investigation of HCN production in reducing atmospheric conditions (89-95% H$_2$) possibly representing the earliest stages of the Hadean eon, ~4.5-4.3 billion years ago. We make use of cold plasma discharges - a laboratory analog to shortwave UV radiation - to simulate HCN production in the upper layers of the atmosphere for CH$_4$ abundances ranging from 0.1-6.5%. We then combine experimental mass spectrum measurements with our theoretical plasma models to estimate the HCN concentrations produced in our experiments. We find that upper atmospheric HCN production scales linearly with CH$_4$ abundance with the relation [HCN] = 0.13 $\pm$ 0.01[CH$_4$]. Concentrations of HCN near the surface of the Hadean Earth are expected to be about 2-3 orders of magnitude lower. The addition of 1% water to our experiments results in a ~50% reduction in HCN production. We find that four reactions are primarily responsible for HCN production in our experiments: (i) $^4$N + CH$_3$ -> H$_2$CN + H -> HCN + H$_2$, (ii) $^4$N + CH -> CN + H followed by CN + CH$_4$ -> HCN + CH$_3$, (iii) C$_2$H$_4$ + $^4$N -> HCN + CH$_3$, and (iv) $^4$N + $^3$CH$_2$ -> HCN + H. The most prebiotically favorable Hadean atmosphere would have been very rich in CH$_4$ (> 5%), and as a result of greenhouse effects the surface would be likely very hot. In such a prebiotic scenario, it may have been important to incorporate HCN into organic hazes that could later release biomolecules and precursors into the first ponds.
