荷电纳米水合氨团簇的Fission--成核过程的微观研究
Fission of charged nano-hydrated ammonia clusters -- microscopic insights on the nucleation processes
摘要：
虽然在宏观尺度上进行了大量研究，但在分子水平上对大气气溶胶中导致成核和裂变过程的动力学仍然知之甚少。在这里，我们提出了一个联合的实验-理论研究的模型系统组成的氢键氨和水分子。实验上，团簇是通过绝热共膨胀产生的。利用同步辐射制备了双电离离子产物，并用符合质量和3D动量谱进行了分析。使用从头计算分子动力学进行计算，以了解在第一个500 fs的碎片。进一步探索的势能面进行了理论的DFT水平，以获得信息的能量的过程。水被认为是一种有效的纳米液滴稳定剂，并且发现即使在低含水量下也具有显著的效果。在分子水平上，水的稳定作用可能与氨分子和团簇表面富含水的环境之间的离解能增加有关。此外，我们的研究结果支持的作用，铵作为一个载流子在溶液中，优先绑定到周围的氨分子，这可以影响大气成核过程。
英文摘要：
While largely studied on the macroscopic scale, the dynamics leading to nucleation and fission processes in atmospheric aerosols are still poorly understood at the molecular level. Here, we present a joint experimental-theoretical study of a model system consisting of hydrogen-bonded ammonia and water molecules. Experimentally, the clusters were produced via adiabatic co-expansion. Double ionization ionic products were prepared using synchrotron radiation and analyzed with coincident mass- and 3D momentum spectroscopy. Calculations were carried out using ab initio molecular dynamics to understand the fragmentation within the first 500 fs. Further exploration of the potential energy surfaces were performed at a DFT level of theory to gain information on the energetics of the processes. Water was identified as an efficient nano-droplet stabilizer, and is found to have a significant effect even at low water content. On the molecular level, the stabilizing role of water can be related to an increase in the dissociation energy between ammonia molecules and the water enriched environment at the cluster surface. Furthermore, our results support the role of ammonium as a charge carrier in the solution, preferentially bound to surrounding ammonia molecules, which can influence atmospheric nucleation process.
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