Reactions of dinitrogen pentoxide (N2O5) greatly affect the concentrations of NO3, ozone, OH radicals, methane, and more. In this work, we employ ab initio molecular dynamics and other tools of computational chemistry to explore reactions of N2O5 with anions hydrated by 12 water molecules to shed light on this important class of reactions. The ions investigated are Cl-, SO42-, ClO4-, and RCOO- (R = H, CH3, C2H5). The following main results are obtained: (i) all the reactions take place by an SN2-type mechanism, with a transition state that involves a contact ion pair (NO2+NO3-) that interacts strongly with water molecules. (ii) Reactions of a solvent-separated nitronium ion (NO2+) are not observed in any of the cases. (iii) An explanation is provided for the suppression of ClNO2 formation from N2O5 reacting with salty water when sulfate or acetate ions are present, as found in recent experiments. (iv) Formation of novel intermediate species, such as (SO4NO2-) and RCOONO2, in these reactions is predicted. The results suggest atomistic-level mechanisms for the reactions studied and may be useful for the development of improved modeling of reaction kinetics in aerosol particles.

中文翻译：

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N2O5与水中离子的SN2反应：微观机理，中间体和产物。

五氧化二氮（N2O5）​​的反应极大地影响了NO3，臭氧，OH自由基，甲烷等的浓度。在这项工作中，我们使用从头算分子动力学和其他化学计算工具来探索N2O5与12个水分子水合阴离子的反应，以阐明这一重要的反应类别。研究的离子为Cl-，SO42-，ClO4-和RCOO-（R = H，CH3，C2H5）。得到以下主要结果：（i）所有反应都是通过SN2型机理发生的，其过渡态包括与水分子强烈相互作用的接触离子对（NO2 + NO3-）。（ii）在任何情况下都没有观察到溶剂分离的硝基离子（NO 2+）的反应。（iii）提供了一种解释，用于抑制当存在硫酸根或乙酸根离子时，N2O5与盐水反应时ClNO2的形成，正如最近的实验所发现的那样。（iv）预测在这些反应中会形成新的中间物种，例如（SO4NO2-）和RCOONO2。结果表明所研究反应的原子级机理，可能对改进气溶胶颗粒中反应动力学的建模有用。