N $_2$ O $_5$在水溶液气溶胶中的反应性摄取机理
Elucidating the mechanism of reactive uptake of N$_2$O$_5$ in aqueous aerosol
摘要：
通过N $_2$ O $_5$的反应性吸收进入含水气溶胶，几乎三分之一的氮氧化物从大气中被去除。反应性摄取的主要步骤是N $_2$ O $_5$的快速水解，尽管进行了大量研究，但该过程的机制和速率尚不清楚。在这里，我们使用基于机器学习的反应性多体势和重要性抽样分子动力学模拟的方法来研究N $_2$ O $_5$的溶剂化和随后的水解。我们发现，水解到硝酸通过协调波动的分子内电荷分离和溶剂化，其特征速率为4.1 ns $^{-1}$，数量级快于传统的假设。这种大的速率使人们对反应性吸收的标准模型提出了质疑，该模型设想了气体和本体溶液之间的局部平衡。我们提出了一个替代模型的基础上，界面反应，可以解释现有的实验观察，并证实了明确的模拟。
英文摘要：
Nearly one third of all nitrogen oxides are removed from the atmosphere through the reactive uptake of N$_2$O$_5$ into aqueous aerosol. The primary step in reactive uptake is the rapid hydrolysis of N$_2$O$_5$, yet despite significant study, the mechanism and rate of this process are unknown. Here we use machine learning-based reactive many body potentials and methods of importance sampling molecular dynamics simulations to study the solvation and subsequent hydrolysis of N$_2$O$_5$. We find that hydrolysis to nitric acid proceeds through the coordinated fluctuation of intramolecular charge separation and solvation, and its characteristic rate is 4.1 ns$^{-1}$, orders of magnitude faster than traditionally assumed. This large rate calls into question standard models of reactive uptake that envision local equilibration between the gas and the bulk solution. We propose an alternative model based on interfacial reactivity that can explain existing experimental observations and is corroborated by explicit simulations.
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