Theoretical study on the dissociation of HCl-(H2O)1-30 and HNO3-(H2O)1-30 clusters

Abstract

HCl-(H2O)n and HNO3-(H2O)n clusters are HCl complexes and HNO3 complexes constituted by small assemblies of n water molecules forming hydrogen bond network with HCl and HNO3, respectively. Herein, a comparative study on HCl-(H2O)n and HNO3-(H2O)n (n <= 29) is performed at the B3LYP-D3, omega B97XD, M06-2x, and MP2 levels with the 6-31 + G(d,p) basis set, focusing on hydrogen bonding interactions, relative stabilities, cooperativity energies, NBO charge transfer and vibration of H3O+. The results show that water clusters tend to stabilize more HNO3 than HCl based on computed binding energies and cooperativity energies. At least four and five water molecules are required for a total dissociation of HCl and HNO3, respectively. Comparison between endohedral and exohedral clusters HCl-(H2O)n and HNO3-(H2O)n (n = 19-20, 27-29) shows that chloride and nitrate are more stabilized inside the cage, unlike H3O+ which prefers laying on the cluster surface. The third overtones of O-H mode of H3O+ in HCl-water and HNO3-water large clusters are found to be in good agreement with experiments laying around 9000-7700 cm-1.