Equilibrium configuration of (H2O)n, for n = 1–3

Abstract

The equilibrium configurations of water molecule (H2O)n=1, its dimer (H2O)n=2 and trimer (H2O)n=3 have been studied in this paper. The ionic character of the OHO hydrogen bond, formed between the electronegative oxygen atoms, in (H2O)n=2, appears as a change in bond lengths in one of the water molecules while the bond lengths in the other molecule remain same as in (H2O)n=1. The increased hydrogen bond strength, caused by the cooperative effect of three-body forces (H2O)n=3, as compared to (H2O)n=2, results in the equilibrium structure of the water trimer to be much more rigid than that of the dimer. An attempt has been made, from the energy standpoint, to understand the controversy on chemical formula of water as H2O or H1·5O by studying the equilibrium configuration of (H2O) OH, which corresponds to 2H1·5O. The ground-state energy of (H2O) OH is found to be lower than the sum of the ground-state energies of OH and H2O at infinite separation. Calculations also show the ground-state energy of (H2O) OH to be lower than the sum of the energies of the constituent atoms at infinite separation. This shows that the binding energy of (H2O) OH is positive, which indicates that (H2O) OH is relatively stable.