标题： CO2在气-水界面的水合：一种表面介导的“进出”机制 显示英文标题

标题： CO2 Hydration at the Air-Water Interface: A Surface-Mediated 'In and Out' Mechanism

摘要： 对CO$_2$ + H$_2$O水合反应的理解对于模拟海洋酸化的影响、实现新的碳储存解决方案以及作为地球科学中的模型过程至关重要。 尽管该反应的机制已在凝聚相中得到了广泛研究，但在气-水界面处的机制仍然不明确，使得表面吸附的CO$_2$对整体酸化反应的贡献仍不确定。 在本研究中，我们采用训练到不同理论水平的机器学习势能函数，以提供对气-水界面处CO$_2$水合的分子级理解。 我们表明，界面处的反应遵循一种表面介导的“进入和出去”机制：CO$_2$扩散到水相表面层，与水反应生成碳酸，并随后被从溶液中排出。 我们表明，这种表面层提供了一个类似于体相的溶剂化环境，导致体相和界面过程具有相似的反应性以及几乎相同的自由能曲线。 我们的研究揭示了一种新的、非常规的反应机制，强调了气-水界面分子反应位点的动态性质。 体相和界面曲线之间的相似性表明，在这两种溶剂化环境中，CO$_2$的水合同样可行，并且酸化速率可能因这一额外的表面贡献而增强。 显示英文摘要

摘要： An understanding of the CO$_2$ + H$_2$O hydration reaction is crucial for modeling the effects of ocean acidification, for enabling novel carbon storage solutions, and as a model process in the geosciences. While the mechanism of this reaction has been investigated extensively in the condensed phase, its mechanism at the air-water interface remains elusive, leaving uncertain the contribution that surface-adsorbed CO$_2$ makes to the overall acidification reaction. In this study, we employ machine-learned potentials trained to various levels of theory to provide a molecular-level understanding of CO$_2$ hydration at the air-water interface. We show that reaction at the interface follows a surface-mediated `In and Out' mechanism: CO$_2$ diffuses into the aqueous surface layer, reacts to form carbonic acid, and is subsequently expelled from solution. We show that this surface layer provides a bulk-like solvation environment, engendering similar modes of reactivity and near-identical free energy profiles for the bulk and interfacial processes. Our study unveils a new, unconventional reaction mechanism that underscores the dynamic nature of the molecular reaction site at the air-water interface. The similarity between bulk and interfacial profiles shows that CO$_2$ hydration is equally as feasible under these two solvation environments and that acidification rates are likely enhanced by this additional surface contribution.