Establishing the structural motifs present in small ammonium and aminium bisulfate clusters of relevance to atmospheric new particle formation
Establishing the structural motifs present in small ammonium and aminium bisulfate clusters of relevance to atmospheric new particle formation
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DOI：
10.1063/5.0015094
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发表时间：
2020-07-21
影响因子：
4.4
通讯作者：
Johnson, Christopher J.
中科院分区：
文献类型：
--
作者：
Kreinbihl, John J.;Frederiks, Nicoline C.;Johnson, Christopher J.
大气新粒子形成是大气痕量气体（通常为酸和碱）聚集并生长成潜在气候相关粒子的过程。在这里，我们评估的结构和结构图案存在于小的阳离子铵和铵硫酸氢盐集群已被研究实验和计算作为新粒子的种子。对于几个以前研究的集群，多个不同的最低能量结构已被预测。振动光谱的质量选择集群和量子化学计算允许我们分配的最小能量结构的最小阳离子簇的两个铵离子和一个硫酸氢根离子的C-S-对称结构，是持久的胺取代。我们推导出关键硫酸氢盐振动的唯象振动频率标度因子，以帮助比较较大簇的实验和计算光谱。最后，我们确定了一个以前未分配的分子间硫酸氢盐-硫酸氢盐氢键的光谱标记，并表明它存在于一类结构中，这些结构的能量都低于任何以前报道的结构。跟踪该标记表明，该基序在较大的簇中是突出的，并且类似于180 nm的硫酸氢铵颗粒。总之，这些结果建立了一套结构图案负责绑定的气体在表面生长的集群，充分解释了大颗粒的光谱，并提供基准的努力，以改善结构的预测，这是至关重要的准确的理论处理这一过程。
Atmospheric new particle formation is the process by which atmospheric trace gases, typically acids and bases, cluster and grow into potentially climatically relevant particles. Here, we evaluate the structures and structural motifs present in small cationic ammonium and aminium bisulfate clusters that have been studied both experimentally and computationally as seeds for new particles. For several previously studied clusters, multiple different minimum-energy structures have been predicted. Vibrational spectra of mass-selected clusters and quantum chemical calculations allow us to assign the minimum-energy structure for the smallest cationic cluster of two ammonium ions and one bisulfate ion to a C-S-symmetry structure that is persistent under amine substitution. We derive phenomenological vibrational frequency scaling factors for key bisulfate vibrations to aid in the comparison of experimental and computed spectra of larger clusters. Finally, we identify a previously unassigned spectral marker for intermolecular bisulfate-bisulfate hydrogen bonds and show that it is present in a class of structures that are all lower in energy than any previously reported structure. Tracking this marker suggests that this motif is prominent in larger clusters as well as similar to 180 nm ammonium bisulfate particles. Taken together, these results establish a set of structural motifs responsible for binding of gases at the surface of growing clusters that fully explain the spectrum of large particles and provide benchmarks for efforts to improve structure predictions, which are critical for the accurate theoretical treatment of this process.