The structure of aqueous electrolyte solutions and some problems in neutron scattering from water.

The nature of ion-ion ordering in aqueous electrolyte solutions above one molal is investigated and results also presented for inelastic scattering corrections in water. Some experimental work on concentrated aqueous solutions, which had been previously interpreted to imply quasi-lattice ordering in these solutions has been shown to be consistent with a large hard sphere fluid model of the solute ions in solution. The forces that could be responsible for quasi-lattice ordering in aqueous electrolyte solutions are investigated and a previous suggestion that the ion-induced dipole or cavity repulsion between hydrated ions provided such a force is shown to be incorrect. New models of quasi-lattice electrolyte solutions are presented and free energies calculated from them. By comparing the excess free energy derived from these models with that measured experimentally it is clearly seen that agreement depends upon introducing an amount of disorder which may be inconsistent with a meaningful concept of quasi-lattice ion-ion ordering. Inelastic scattering corrections are estimated for the experimentally important cases of light and heavy water via the use of a molecular dynamics simulation of water. The method used requires further theoretical work before exact results can be obtained.