Nuclear Spin Saturation by Ultrasonics in Sodium Chloride

Abstract

An ultrasonic vibrational mode with rather well-defined properties has been set up in a cylindrical single crystal of sodium chloride. The saturation of the spin levels of ${\mathrm{Na}}^{23}$ and ${\mathrm{Cl}}^{35}$ by acoustically induced quadrupole transitions, $\ensuremath{\Delta}m=\ifmmode\pm\else\textpm\fi{}2$, has been measured in the steady state by a standard nuclear magnetic resonance technique, for several orientations of the ultrasonic wave and external magnetic fields. The components of the fourth-order tensor connecting the electrical field gradient tensor at the nuclei with the strain deformation tensor have been determined. The components satisfy an isotropy condition rather than the Cauchy relation. The results show the inadequacy of the ionic point-charge model coupled with an isotropic Sternheimer antishielding factor. The interpretation of the data requires a considerable amount of covalent character and configurational interaction on the ${\mathrm{Na}}^{+}$ ion.