TEMPERATURE EFFECTS ON THE ROTATIONAL MOTION OF THE COORDINATED D2O MOLECULES IN LIBR AQUEOUS-SOLUTIONS STUDIED BY D-2 AND O-17 NMR RELAXATION

The spin-lattice relaxation times (T-1) of D-2 and O-17 nuclei of coordinated heavy water (D2O) molecules for Li+ in lithium bromide aqueous solutions Here measured in the range of 5-50 degrees C by means of NMR. The spin-lattice relaxation rates (R(1) = 1/T-1) varied linearly with the concentration up to 1 mol/kg at a given temperature. The parallel (D-2) and the perpendicular (O-17) rotational correlation times ( tau ) of coordinated D2O molecules for Li+ were determined. The ratio tau (D-2)/ tau (O-17) of the coordinated D2O molecules for Li+ was larger than unity and was practically independent of temperature, which indicated that the rotational anisotropies of coordinated D2O molecules for Li+ was almost temperature independent. The activation energy of rotation of coordinated D2O molecules for Li+ was larger than that of D2O molecules in pure liquid, which related to the orientation of the D2O molecule in the (first) hydration shell of Li+.