arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1601.01696astro-ph.GAastro-ph.SR
收藏

星前核气相HCO和CH3O自由基的起源

The origin of gas-phase HCO and CH3O radicals in prestellar cores

Aurore Bacmann, Alexandre Faure

备注：
accepted by A&A
发表信息：
A&A 587, A130 (2016)
阅读 PDF
arXiv 页面 ↗HTML 原文 ↗

摘要：

最近意外地检测到陆地复杂的有机分子在冷（~ 10 K）的气体，这些物种的普遍接受的形成机制提出了质疑。标准的气相机制效率低下，往往生产这些分子不足，许多关键的反应涉及不受约束。晶粒表面机制，这是一个可行的替代方案，遭受的事实，他们依赖于重自由基，这是不可能的热在非常低的温度下的晶粒表面扩散。甲醇是地球上最简单的复杂有机分子之一，被认为是在CO上连续添加H原子后在冷颗粒表面形成的。与较重的物质不同，即使在10 K下，H原子在颗粒表面也非常活跃。参与谷物表面CO加氢甲醇形成的中间物种是自由基HCO和CH 3 O，以及稳定物种甲醛H2 CO。这些自由基被认为是谷物表面复杂有机分子的前体。我们提出了新的观测的HCO和CH 3 O自由基在星前核心的样品，并进行了分析的物种HCO，H2 CO，CH 3 O，和CH 3OH，这代表了不同阶段的颗粒表面氢化CO CH 3OH的丰度。在我们的样品的所有来源中，CO在谷物上的氢化反应中的各种中间物种之间的丰度比是相似的，HCO：H2 CO：CH 3 O：CH 3OH ~ 10：100：1：100。我们认为，这些比率可能不代表的原始丰度的晶粒，但相反，表明自由基HCO和CH 3 O的气相产物的前体H2 CO和CH 3OH，分别。气相途径被认为是简单的估计HCO和CH 3 O丰度进行比较的意见。临界反应速率常数，分支比，和中间物种的最后确定。

英文摘要：

The recent unexpected detection of terrestrial complex organic molecules in the cold (~ 10 K) gas has cast doubts on the commonly accepted formation mechanisms of these species. Standard gas-phase mechanisms are inefficient and tend to underproduce these molecules, and many of the key reactions involved are unconstrained. Grain-surface mechanisms, which were presented as a viable alternative, suffer from the fact that they rely on grain surface diffusion of heavy radicals, which is not possible thermally at very low temperatures. One of the simplest terrestrial complex organic molecules, methanol is believed to form on cold grain surfaces following from successive H atom additions on CO. Unlike heavier species, H atoms are very mobile on grain surfaces even at 10 K. Intermediate species involved in grain surface methanol formation by CO hydrogenation are the radicals HCO and CH3O, as well as the stable species formaldehyde H2CO. These radicals are thought to be precursors of complex organic molecules on grain surfaces. We present new observations of the HCO and CH3O radicals in a sample of prestellar cores and carry out an analysis of the abundances of the species HCO, H2CO, CH3O, and CH3OH, which represent the various stages of grain-surface hydrogenation of CO to CH3OH. The abundance ratios between the various intermediate species in the hydrogenation reaction of CO on grains are similar in all sources of our sample, HCO:H2CO:CH3O:CH3OH ~ 10:100:1:100. We argue that these ratios may not be representative of the primordial abundances on the grains but, rather, suggest that the radicals HCO and CH3O are gas-phase products of the precursors H2CO and CH3OH, respectively. Gas-phase pathways are considered and simple estimates of HCO and CH3O abundances are compared to the observations. Critical reaction rate constants, branching ratios, and intermediate species are finally identified.

机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。

↑