A theoretical study of the ionic dissociation of HF, HCl, and H2S in water clusters

The ionic dissociation of HF, HCl, and H2S in water is examined using density functional theory (DFT), Hartree-Fock (HF), acid Moller-Plesset theory to second order (MP2). The calculations show that HF, HCl, and H2S form fully dissociated stable clusters with four water molecules. Each cluster appears to be stabilized by the formation of six hydrogen bonds. These calculations also indicate that a minimum of four water molecules are required to form stable structures in which positive and negative ions coexist in the cluster. The hydrogen transfer between the acid and water molecules is very similar to the mechanism proposed for hydrogen transfer in water solutions. The binding energies of the hydrated hydrofluoric acid, hydrated hydrochloric acid, and hydrated hydrogen disulfide estimated with B-LYP are 37.51, 41.17, and 20.68 kcal/mol, respectively. (C) 1996 American Institute of Physics.