深入探索无定形固态水表面的催化位点：I. 氨基甲醇的天体合成
In-Depth Exploration of Catalytic Sites on Amorphous Solid Water: I. The Astrosynthesis of Aminomethanol
AI总结：
本文利用密度泛函理论研究无定形固态水表面对氨与甲醛反应生成氨基甲醇的催化作用，识别出四类催化位点和14条反应路径，揭示了低能反应机理的关键在于表面悬挂OH键的存在。
摘要：
发生在冰粒幔上的化学过程对于星际环境中的复杂化学至关重要。在本研究中，我们利用密度泛函理论，对无定形固态水（ASW）表面对氨（NH$_3$）与甲醛（H$_2$CO）反应生成氨基甲醇（NH$_2$CH$_2$OH）的催化效应进行了全面分析。我们基于由22个水分子组成的团簇表面模型，根据NH$_3$和H$_2$CO反应物的结合能分布识别了潜在的催化位点，并共发现了14条反应路径。我们的结果表明，根据反应物复合物中羰基氧和氨基与冰表面的相互作用，催化位点可分为四类。利用内禀反应坐标和反应力分析对反应机理的详细研究揭示了该反应的三个不同化学事件：C--N键的形成、N--H键的断裂以及O--H羟基键的形成。根据催化位点的类型，这些事件可以在一个单一、协同但不同步的步骤中发生，也可以在逐步机理中被分离开来，其中观察到的最低总过渡态能量为1.3 kcal mol$^{-1}$。低能机理的一个关键要求是表面上存在一对悬挂OH键，这种位点占ASW多孔表面上潜在催化位点的5%。
英文摘要：
Chemical processes taking place on ice-grain mantles are pivotal to the complex chemistry of interstellar environments. In this study, we conducted a comprehensive analysis of the catalytic effects of an amorphous solid water (ASW) surface on the reaction between ammonia (NH$_3$) and formaldehyde (H$_2$CO) to form aminomethanol (NH$_2$CH$_2$OH) using density functional theory. We identified potential catalytic sites based on the binding energy distribution of NH$_3$ and H$_2$CO reactants, on a set-of-clusters surface model composed of 22 water molecules and found a total of 14 reaction paths. Our results indicate that the catalytic sites can be categorized into four groups, depending on the interactions of the carbonyl oxygen and the amino group with the ice surface in the reactant complex. A detailed analysis of the reaction mechanism using Intrinsic Reaction Coordinate and reaction force analysis revealed three distinct chemical events for this reaction: formation of the C--N bond, breaking of the N--H bond, and formation of the O--H hydroxyl bond. Depending on the type of catalytic site, these events can occur within a single, concerted, albeit asynchronous, step, or can be isolated in a step-wise mechanism, with the lowest overall transition state energy observed at 1.3 kcal mol$^{-1}$. A key requirement for the low-energy mechanism is the presence of a pair of dangling OH bonds on the surface, found at 5\% of the potential catalytic sites on an ASW porous surface.
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