Theoretical study of proton transfer in ammonia–hydrogen halides in the presence of methanol

Abstract

In this work, the effect of solvent (methanol, CH3OH) molecules on proton transfer (PT) between ammonia and hydrogen halides was studied. We performed MP2 and B3LYP calculations on HX–NH3–(CH3OH) n clusters for three hydrogen halides, HF, HCl, and HBr, with the number of methanol molecules varying from none to three (n = 0–3). The results showed that stepwise association of methanol molecules with the gas-phase complex can eventually facilitate ionization within the complex, producing the $$ {\text{NH}}_{4}^{ + } {\text{X}}^{ - } - \left( {{\text{CH}}_{ 3} {\text{OH}}} \right)_{\text{n}} $$ cluster. We found that PT occurs on addition of from one (for HBr) to three (for HF) methanol molecules. The interaction energy $$ E_{\text{int}} $$ and $$ \Updelta E_{\text{add}} $$ for the complexes were calculated and basis set superposition error (BSSE) correction was also performed. Atoms-in-molecule and natural-bond-orbital analysis were used to study the properties of the hydrogen bonds in the complexes.