Proton relaxation times in alkali halide solutions

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Abstract
Measurements of the proton spin-lattice relaxation times as a function of concentration in aqueous alkali halide solutions are used to investigate the interactions between the ions and water molecules. A simplified model of a solution is employed in which local proton relaxation times are assigned to three different sites: those near the anion, those near the cation and those not near any ion. A procedure is worked out to calculate the local relaxation times and the number of nearest-neighbour water molecules using the data and the B-viscosity-coefficients of the solutions. Differences in the activation energies for a change in configuration about an ion relative to pure water are obtained. These indicate that the configurations of water molecules around the lithium, sodium and fluorine ions are more stable than in pure water, while those configurations about all other ions are less stable. Furthermore, the degree of stability decreases with increasing ionic radius.