Study of the structure of molecular complexes. V. Heat of formation for the Li+, Na+, K+, F−, and Cl− ion complexes with a single water molecule

Abstract

In order to obtain the heat of formation ΔH, for the ion‐water complexes previously studied in the Hartree‐Fock approximation in the first three papers of this series, we have computed the normal frequencies of the complexes, the zero‐point energy correction to ΔH, and the molecular extra correlation energy. The main contribution to ΔH is due to the Hartree‐Fock binding; the least important contribution results from the correlation effects. The Hartree‐Fock binding varies from about 35 kcal/mole (Li⁺–H₂O) to about 12 kcal/mole (Cl⁻–H₂O); the zero‐point correction is between 1 and 2 kcal/mole; and the molecular extra correlation correction is less than 1 kcal/mole. The computation of ΔH is analyzed in order to estimate upper and lower bounds. We conclude that the calculated ΔH values are accurate to about 2.0 kcal/mole. Experimental data support this conclusion. In the Appendix, the potentials for water‐ion complexes have been presented in the form of a simple analytical expansion. The expansion has been obtained by fitting the Hartree‐Fock computed energies for the water‐ion complexes.