Kreinbihl John J, Frederiks Nicoline C, Johnson Christopher J
Department of Chemistry, Stony Brook University, 100 Nicolls Road, Stony Brook, New York 11794-3400, USA.
J Chem Phys. 2021 Jan 7;154(1):014304. doi: 10.1063/5.0037965.
The role of water in the formation of particles from atmospheric trace gases is not well understood, in large part due to difficulties in detecting its presence under atmospheric conditions and the variety of possible structures that must be screened computationally. Here, we use infrared spectroscopy and variable-temperature ion trap mass spectrometry to investigate the structural motifs adopted by water bound to ammonium bisulfate clusters and their temperature dependence. For clusters featuring only acid-base linkages, water adopts a bridging arrangement spanning an adjacent ammonium and bisulfate. For larger clusters, water can also insert into a bisulfate-bisulfate hydrogen bond, yielding hydration isomers with very similar binding energies. The population of these isomers shows a complex temperature evolution, as an apparent third isomer appears with a temperature dependence that is difficult to explain using simple thermodynamic arguments. These observations suggest that the thermodynamics of water binding to atmospheric clusters such as these may not be straightforward.
水在由大气痕量气体形成颗粒过程中的作用尚未得到充分理解，这在很大程度上是由于在大气条件下检测其存在存在困难，以及必须通过计算筛选的各种可能结构。在这里，我们使用红外光谱和可变温度离子阱质谱来研究与硫酸氢铵簇结合的水所采用的结构模式及其温度依赖性。对于仅具有酸碱键的簇，水采用跨越相邻铵和硫酸氢根的桥连排列。对于更大的簇，水也可以插入硫酸氢根 - 硫酸氢根氢键中，产生具有非常相似结合能的水合异构体。这些异构体的丰度呈现出复杂的温度演化，因为一种明显的第三种异构体出现，其温度依赖性难以用简单的热力学论点来解释。这些观察结果表明，水与这类大气簇结合的热力学可能并非简单直接。
