Nuclear Quadrupole Coupling in the Li2 Molecule

Abstract

The method of deformed atoms in molecules is applied to calculate the electric field gradient q at a nucleus in Li₂, using the molecular wave function obtained by Arai and Sakamoto. The field gradient is composed of nuclear and electronic terms which almost cancel each other, so that its magnitude and even its sign are seriously affected by accuracy of wave functions used. It is nevertheless expected that the A. S. wave function, which gives a dissociation energy of 0.96 ev compared with the experimental value of 1.05 ev, is sufficiently accurate. Neglecting the shielding effect induced in the 1s shell by the nuclear quadrupole moment Q, the result obtained is q/2e=q′=—0.0034 au at an internuclear distance of 4.93 au. The nuclear quadrupole coupling constant eqQ found experimentally is positive (+0.060 Mc/sec). A negative value of the quadrupole moment Q(Li⁷) thus is obtained, in agreement with the prediction of the nuclear shell model.