With the advent of JWST ice observations, dedicated studies on the formation reactions of detected molecules are becoming increasingly important. One of the most interesting molecules in interstellar ice is CO2. Despite its simplicity, the main formation reaction considered, CO + OH → CO2 + H through the energetic HOCO* intermediate on ice dust, is subject to uncertainty because it directly competes with the stabilization of HOCO as a final product, which is formed through energy dissipation of HOCO* to the water ice. When energy dissipation to the surface is effective during the reaction, HOCO can be a dominant product. In this study, we experimentally demonstrate that the major product of the reaction is indeed not CO2, but rather the highly reactive radical HOCO. The HOCO radical can later evolve into CO2 through H-abstraction reactions, but these reactions compete with additional reactions, leading to the formation of carboxylic acids (R-COOH). Our results highlight the importance of HOCO chemistry and encourage further exploration of the chemistry of this radical.

中文翻译：

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HOCO 化学的重要性：冰尘上的 CO 和 OH 反应低效形成 CO2


随着 JWST 冰观测的出现，对检测到的分子的形成反应的专门研究变得越来越重要。星际冰中最有趣的分子之一是 CO2。尽管它很简单，但所考虑的主要形成反应，即 CO + OH → CO2 + H 通过冰尘上的含能 HOCO* 中间体，存在不确定性，因为它直接与 HOCO 作为最终产物的稳定化竞争，后者是通过 HOCO* 的能量耗散到水冰中形成的。当反应过程中能量耗散到表面有效时，HOCO 可以成为主要产物。在这项研究中，我们通过实验证明，反应的主要产物确实不是 CO2，而是高反应性自由基 HOCO。HOCO 自由基稍后可以通过 H 提取反应释放成 CO2，但这些反应会与其他反应竞争，导致羧酸 （R-COOH） 的形成。我们的结果突出了 HOCO 化学的重要性，并鼓励进一步探索这种自由基的化学性质。