Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA.
J Phys Chem A. 2010 Nov 4;114(43):11638-44. doi: 10.1021/jp106363m.
The reaction kinetics of ammonium bisulfate clusters with dimethylamine (DMA) gas were investigated using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Clusters ranged in size from 1 to 10 bisulfate ions. Although displacement of the first several ammonium ions by DMA occurred with near unit efficiency, displacement of the final ammonium ion was cluster size dependent. For small clusters, all ammonium ions are exposed to incoming DMA molecules, allowing for facile exchange ("surface" exchange). However, with increasing cluster size, an ammonium ion can be trapped in an inaccessible region of the cluster ("core" exchange), thereby rendering exchange difficult. DMA was also observed to add onto existing dimethylaminium bisulfate clusters above a critical size, whereas ammonia did not add onto ammonium bisulfate clusters. The results suggest that as the cluster size increases, di-dimethylaminium sulfate formation becomes more favorable. The results of this study give further evidence to suggest that ambient sub-3 nm diameter particles are likely to contain aminium salts rather than ammonium salts.
使用傅里叶变换离子回旋共振质谱（FTICR-MS）研究了硫酸氢铵簇与二甲胺（DMA）气体的反应动力学。簇的大小范围为 1 到 10 个硫酸氢根离子。尽管 DMA 几乎可以以单位效率取代前几个氨离子，但最后一个氨离子的取代与簇的大小有关。对于小簇，所有的氨离子都暴露于进入的 DMA 分子，允许易于交换（“表面”交换）。然而，随着簇的增大，一个氨离子可以被困在簇的不可接近区域（“核心”交换），从而使交换变得困难。DMA 也被观察到在超过临界尺寸的情况下添加到现有的二甲基氨基硫酸氢盐簇上，而氨则不会添加到硫酸氢铵簇上。结果表明，随着簇的增大，二甲基硫酸铵的形成变得更加有利。本研究的结果进一步表明，环境中直径小于 3nm 的亚颗粒可能含有铵盐而不是氨盐。
