RELAXATION RATES OF ALKALI METAL AND CHLORIDE NUCLEI IN AQUEOUS SOLUTION . QUADRUPOLE MOMENT OF 133CS

Relaxation rates of 7Li+, 23Na +, 87Rb+, 133Cs+, and 35C1- in aqueous salt solutions have been measured at 297°K at various salt concentrations and extrapolated to infinite dilution. Relaxation rates increased in proportion to viscosity (except for 7Li-) in deuterium oxide solutions, demonstrating that the relaxation mechanism is via the electric quadrupole moment of the solute nuclei interacting with fluctuating electricfield gradients produced by the solvent molecules. A general expression for the relaxation rate is given; it was found that the correlation time for the solute-nucleus-solvent-molecule interaction is a slowly varying function of ionic radius of the solute nucleus. The nuclear electric quadrupole moment (Q) of 133Cs is calculated from the relaxation rate of 133Cs in CsI solutions and the observed mechanism of the relaxation process. The calculated value of | Q | =(2.3±0.3) × 1027 cm2 is somewhat smaller than the previously reported value derived from the nuclear optical double resonance technique.