Isotope effects on the reorientational motion of hydrated H2O molecules in alkali metal bromide dilute aqueous solutions studied by NMR spectroscopy

Abstract

The spin-lattice relaxation times of 1H and 17O nuclei of hydrated H2O molecules in alkali metal bromide (LiBr, NaBr, KBr, and CsBr) dilute aqueous solutions in the concentration range from 0.2 to l.0 mol kg-1 at 25°C were measured by NMR spectroscopy. The reorientational correlation times for the intramolecular 1H-1H (τ+hh) and 1H-17O (τ+OH) axes, as well as the perpendicular axis (17O nuclei, τ+17O) to the molecular plane of a hydrated H2O molecule were determied. The two reorientational correlation times (τ+Hh and τ+Oh) of pure H2O and hydrated H2O molecules in Li+, Na+, K+, and Cs+ ions were equal, respectively. Comparing previous data for hydrated D2O molecules with that calculated by using correction values (rHH, rOH, and quadrupolar constant) for H2O molecules, the ratios of τ+D(D2O)/τ+Oh(H2O) and τ+17O(D2O)/τ+17O(H2O) were found to be of the same order as η(D2O)/η(H2O), except for the τ+17Oh(D2O)/τ+17O(H2O) value for the Li+ ion.