Ionic dissociations of chlorosulfonic acid in microsolvated clusters: A density functional theory and ab initio MO study

Ionic dissociation of chlorosulfonic acid (HSO₃Cl) in the molecular clusters HSO₃Cl-(H₂O) _n (n = 1–4) and HSO₃Cl-NH₃-(H₂O) _n (n = 0–3) was investigated by density functional theory and ab initio molecular orbital theory. The equilibrium structures, binding energies, and thermodynamic properties, such as relative enthalpy and relative Gibbs free energy, and were calculated using the hybrid density functional (B3LYP) method and the second order M?ller-Plesset approximation (MP2) method with the 6-311++G** basis set. Chlorosulfonic acid was found to require a minimum of three water molecules for ionization to occur and at least one water molecule to protonate ammonia. The corresponding clusters with fewer water molecules were found to be strongly hydrogen-bonded. The related properties and acid strength of chlorosulfonic acid were discussed and compared to the acid strengths of perchloric acid and sulfuric acid in the context of clusters with ammonia and water. The relative stabilities of these clusters were also investigated. Supported by the National Natural Science Foundation of China (Grant No. 20273046), the Camille and Henry Dreyfus Foundation (Award No. TH-00-028) of California State University, Fullerton, and the Younger Teacher Foundation of Suzhou University (Grant No. Q31094040)