Magnetic relaxation of23Na and81Br in aqueous solutions of the alkali halides

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Abstract
N.M.R. relaxation times of 81Br and 23Na have been measured as a function of temperature and concentration in aqueous solutions of LiBr, NaBr and CsBr. Linewidths of all ions vary linearly with viscosity over temperature, but are not directly proportional to this quantity in contradiction of the Debye equation. Striking similarity exists between the temperature dependence of N.M.R. linewidths and that of dielectric relaxation times in alkali halide solutions, suggesting that solvent reorientation or translation in the outer hydration region is the most efficient means of quadrupolar relaxation. On this assumption approximate solvent tumbling times in outer hydration spheres of Na+ and Br− are calculated. Contributions to relaxation due to ion-ion interactions are in accord with previous theory in that they possess an activation energy of the same approximate magnitude as that for ionic self-diffusion.