Near-Barrierless Ammonium Bisulfate Formation via a Loop-Structure Promoted Proton-Transfer Mechanism on the Surface of Water
Near-Barrierless Ammonium Bisulfate Formation via a Loop-Structure Promoted Proton-Transfer Mechanism on the Surface of Water
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DOI：
10.1021/jacs.5b13048
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发表时间：
2016-02-17
影响因子：
15
通讯作者：
Zeng, Xiao Cheng
中科院分区：
文献类型：
--
作者：
Li, Lei;Kumar, Manoj;Zeng, Xiao Cheng
在大气中，形成硫酸铵的一种众所周知的常规途径是通过水滴中的氨（NH3）中和硫酸。在这里，我们提出了直接从头计算分子动力学模拟证据的水合NH3和SO 3分子在水三聚体以及水滴的表面上形成的硫酸氢铵（NH 4 HSO 4）。该反应提出了一种在大气中形成硫酸铵的新机制，特别是当空气中NH 3浓度高（例如，接近10 μ g m（-3））时。与水单体和二聚体相反，水三聚体通过在反应中心周围形成独特的环结构来实现近无障碍质子转移。环结构的形成促进质子转移中心的水分子分裂，导致NH 4 +/HSO 4-离子对的产生。环结构促进的质子转移机制预计在具有吸附的NH3和SO 3分子的云滴表面上是普遍存在的，因此，可能在气溶胶颗粒的成核中起重要作用（例如，细颗粒物PM2.5）。
In the atmosphere, a well-known and conventional pathway toward the formation of ammonium sulfate is through the neutralization of sulfuric acid with ammonia (NH3) in water droplets. Here, we present direct ab initio molecular dynamics simulation evidence of the formation of ammonium bisulfate (NH4HSO4) from the hydrated NH3 and SO3 molecules in a water trimer as well as on the surface of a water droplet. This reaction suggests a new mechanism for the formation of ammonium sulfate in the atmosphere, especially when the concentration of NH3 is high (e.g. similar to 10 mu g m(-3)) in the air. Contrary to the water monomer and dimer, the water trimer enables near-barrierless proton transfer via the formation of a unique loop structure around the reaction center. The formation of the loop structure promotes the splitting of a water molecule in the proton-transfer center, resulting in the generation a NH4+/HSO4- ion pair. The loop-structure promoted proton-transfer mechanism is expected to be ubiquitous on the surface of cloud droplets with adsorbed NH3 and SO3 molecules and, thus, may play an important role in the nucleation of aerosol particles (e.g., fine particles PM2.5) in water droplets.