Chemical Shift, Relaxation Time, and Electric Quadrupole Coupling in Alkali Halides

Chemical shift and spin lattice relaxation times are measured for Cl 35 in all the alkali chloride crystals and for Br 81 and I 127 in some of the halides. These measured values cannot be explained by using Kondo-Yamashita's theory alone which takes into account the effect of overlap between the central ion and the nearest neighbors. For the chemical shift, it seems that the overlap with the second nearest neighbors is an essential cause of the discrepancy and that the covalent and the electrostatic effects are rather small. If these conclusions are admitted, there must be a large chemical shift (about -2∼-3×10 -4 ) of chlorine ion in aqueous solution relative to the free chlorine ion. A model combining the electrostatic and the overlap effect is proposed to explain reasonably the relaxation times in the crystals. The electric quadrupole coupling in free molecules of alkali halides is also discussed from the present viewpoint. The combination of the electrostatic and the overlap effects seems to give a reasonable explanation for the observed values.