An infrared measurement of chemical desorption from interstellar ice analogues
An infrared measurement of chemical desorption from interstellar ice analogues
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DOI：
10.1038/s41550-018-0380-9
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发表时间：
2018-03
期刊：
影响因子：
14.1
通讯作者：
Y. Oba;T. Tomaru;T. Lamberts;A. Kouchi;N. Watanabe
中科院分区：
文献类型：
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作者：
Y. Oba;T. Tomaru;T. Lamberts;A. Kouchi;N. Watanabe
在温度低至10 K的分子云中，除了氢和氦之外的所有物质都应该被锁定在尘埃颗粒表面的异质冰中。然而，天文观测已经在这些云的气相中检测到150多种不同的物种。分子在低于热解吸温度时从尘埃表面释放出来的机制对于理解这种冷云的化学演变至关重要。由放热反应的过量能量引起的化学解吸在大约50年前首次被提出作为关键的分子释放机制。原则上，化学解吸可以在任何温度下进行，甚至低于热解吸温度。因此，天体化学网络模型通常包括这个过程。虽然有一些以前的实验努力，-，没有红外测量的表面（具有很强的优势，以量化化学解吸）已执行。在这里，我们报告了第一个在反应H + H2S → HS + H2（反应1）和HS + H → H2S（反应2），这是星际硫化学的关键，化学解吸的红外原位测量。本研究清楚地表明，化学解吸是一个更有效的过程中释放到气相中的H2S比以前认为。化学脱附的有效截面表明，在典型的星际环境中，化学脱附速率超过光脱附速率。
In molecular clouds at temperatures as low as 10 K, all species except hydrogen and helium should be locked in the heterogeneous ice on dust grain surfaces. Nevertheless, astronomical observations have detected over 150 different species in the gas phase in these clouds. The mechanism by which molecules are released from the dust surface below thermal desorption temperatures to be detectable in the gas phase is crucial for understanding the chemical evolution in such cold clouds. Chemical desorption, caused by the excess energy of an exothermic reaction, was first proposed as a key molecular release mechanism almost 50 years ago. Chemical desorption can, in principle, take place at any temperature, even below the thermal desorption temperature. Therefore, astrochemical network models commonly include this process,. Although there have been a few previous experimental efforts, –, no infrared measurement of the surface (which has a strong advantage to quantify chemical desorption) has been performed. Here, we report the first infrared in situ measurement of chemical desorption during the reactions H + H2S → HS + H2(reaction 1) and HS + H → H2S (reaction 2), which are key to interstellar sulphur chemistry,. The present study clearly demonstrates that chemical desorption is a more efficient process for releasing H2S into the gas phase than was previously believed. The obtained effective cross-section for chemical desorption indicates that the chemical desorption rate exceeds the photodesorption rate in typical interstellar environments.