Condensation nucleation for ammonia and alkyl-amines with hy-drated sulfuric acid: A theoretical investigations on structures, protonation, and hydrogen bond

The nucleation mechanism for the ternary cluster of hydrated sulfuric acid with ammonia or alkyl-amines is one of the unsettled questions in atmospheric chemistry. The effects of hydration are not be neglected during nucleation. We have investigated the clusters of [(CH)mNH]∙(HSO)∙(HO) with m=0-3 and n=0-14 by molecular dynamics simulation and quantum chemistry. 60 stable conformations were obtained by four different proton-transfer manners at the lever of CAM-B3LYP/6-311G(d,p). Three apparent transitions appeared during non-protonation to single protonation to double protonation with the increasing water. According to binding energy and Gibbs free energy by MP2/6-311++G(d,p), we can conclude that the ability of protonation was related to the alkalinities of ammonia and alkyl-amines in the absence of water. By adding water to enlarge clusters, the dimethylamine was the most favorable to the nucleation due to thermodynamic properties. According to the conformation of clusters, the hydrogen bond was the main interaction during the formation and growth of clusters. When the number of water reached to 5(ammonia), 4(methylamine), 3(dimethylamine), and 4(trimethylamine), the H-bond network began to generate, which indicated the ion-induced interaction between water and HSO/SO can promote the formations of solvent ion-pair and tri-ions isomers beneficially.