电子诱导化学在水和一氧化碳冰中形成甲酸，甲醛和二氧化碳,ACS Earth and Space Chemistry

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电子诱导化学在水和一氧化碳冰中形成甲酸，甲醛和二氧化碳
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2019-07-25 00:00:00 , DOI: 10.1021/acsearthspacechem.9b00168
Fabian Schmidt ₁ , Petra Swiderek ₁ , Jan H. Bredehöft ₁

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已知通过不同类型的辐射处理由水和一氧化碳组成的低温冰会导致形成二氧化碳，甲酸，甲醛以及甲醇。在这项研究中，我们研究了在2至20 eV之间的能量（通常在二次电子中发现的能量范围）下的电子辐照下的这些反应。这是第一次以足够精细的能量步长监测反应，以解析和识别导致特定产物的主要电子-分子相互作用。这使我们能够通过将这些主要的电子-分子相互作用与最终产物联系起来来阐明反应机理。在这些反应中，HCO ^•和HOCO ^•自由基是关键的中间体。我们的结果表明，HCO ^•中间体主要导致甲醛，而HOCO ^•则是甲酸形成的中间体。值得注意的是，通过共振电子附着过程，甲醛和甲酸的形成均在特征能范围内得到增强。相反，导致二氧化碳的反应没有共振能量依赖性，但是可以追溯到非共振中性离解过程。这表明二氧化碳与这两种中间体都不相关。这与先前的实验研究相反，后者已经提出二氧化碳是由HOCO ^•中的H ^•自由基损失而形成的。。但是，我们的结果证实了理论研究的预测，即预测HOCO ^•形成二氧化碳的效率不是很高，因为HOCO ^•具有高能井并很快失去了它在冰基质中可能拥有的多余能量。取而代之的是，我们提供的证据表明，导致水在低温冰和一氧化碳中形成二氧化碳的主要电子分子相互作用是水中和成O原子和H ₂的中性离解。然后，如此形成的O原子直接与一氧化碳反应以产生二氧化碳。

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Formation of Formic Acid, Formaldehyde, and Carbon Dioxide by Electron-Induced Chemistry in Ices of Water and Carbon Monoxide

The processing of cryogenic ices consisting of water and carbon monoxide by different types of radiation is known to lead to the formation of carbon dioxide, formic acid, formaldehyde, and also methanol. In this study, we have investigated these reactions upon electron irradiation with energies between 2 and 20 eV, an energy range typically found in secondary electrons. This is the first time that the reactions have been monitored with a sufficiently fine step width in energy to resolve and identify the primary electron–molecule interactions leading to the specific products. This enables us to elucidate reaction mechanisms by linking these primary electron–molecule interactions to final products. In these reactions, HCO^• and HOCO^• radicals are key intermediates. Our results show that the HCO^• intermediate predominantly leads to formaldehyde, while HOCO^• is intermediate to the formation of formic acid. Noticeably, the formation of both formaldehyde and formic acid is enhanced within characteristic energy ranges by resonant electron attachment processes. In contrast, the reactions leading to carbon dioxide show no resonant energy dependence but can be traced back to nonresonant neutral dissociation processes. This reveals that carbon dioxide is linked to neither of these two intermediates. This is in contrast to prior experimental studies, which have proposed that carbon dioxide is formed by loss of a H^• radical from HOCO^•. However, our results confirm theoretical studies that have predicted that carbon dioxide formation from HOCO^• is not very efficient, because HOCO^• presents an energetic well and quickly loses any excess energy it might have in an ice matrix. Instead, we provide evidence that the primary electron–molecule interaction leading to the formation of carbon dioxide in cryogenic ices of water and carbon monoxide is the neutral dissociation of water into O atoms and H₂. The so-formed O atoms then react directly with carbon monoxide to yield carbon dioxide.

更新日期：2019-07-25

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