Effect of Quenching of Polarizations in Polar Diatomic Molecules on Nuclear-Quadrupole Coupling, Its Vibrational Dependence, and Molecular Dipole Moments

Abstract

A simple model is added to the theory of nuclear-quadrupole coupling, which together with the existing theories, viz., the Townes and Dailey theory and the theory of the antishielding effect, accounts for experimental data on nuclear-quadrupole coupling in the alkali halides. In the ionic configuration of the molecule the polarizations mainly of the halogen ions are assumed to be quenched by the repulsive forces between the ions, insofar as they involve expansion of electron density on the side adjacent to the core of the other ion. For halogen ions this results in a contribution to the electric-field gradient from dipolar polarization, while the antishielding effect is suppressed. This contribution is evaluated by use of experimental data of free halogens. For alkali ions the antishielding effect remains operative. Expressions are derived for the dependence of nuclear-quadrupole coupling on the vibrational state. Quenching of the polarization of halogen ions is also included in Rittner's theory of the electric dipole moment. It is shown that theoretical dipole moments of the alkali halides are consistent with experimental values.