Relaxation Rates of Alkali Metal and Chloride Nuclei in Aqueous Solution. Quadrupole Moment of 133Cs

Relaxation rates of ⁷Li⁺, ²³Na⁺, ⁸⁷Rb⁺, ¹³³Cs⁺, and ³⁵Cl⁻ 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 electric‐field 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 $\mathrm{(Q)}$ 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 ${\text{|\hspace{0.17em}Q\hspace{0.17em}|\hspace{0.17em}=\hspace{0.17em}(2.3\hspace{0.17em}±\hspace{0.17em}0.3)\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−27}}{\mathrm{cm}}^2$ is somewhat smaller than the previously reported value derived from the nuclear optical double resonance technique.