Effect of the Atomic Core on the Nuclear Quadrupole Coupling

The effect of the atomic core on the nuclear quadrupole coupling has been evaluated for several atomic ground states and excited states. It has been shown that for the excited states of the alkalis, as the principal quantum number $n$ is increased, the ratio $R$ of the induced effect to the direct interaction with the valence electron tends toward a constant asymptotic value which is of the same order as for the first excited state (∼-0.1 to -0.3). The sensitivity of $R$ to inaccuracies in the zero-order core wave functions and valence wave functions has been investigated. Equations have been derived for the exchange terms in the quadrupole coupling due to the perturbation of the valence wave function by the nuclear quadrupole moment. The present calculations indicate that the exchange terms do not affect significantly the net antishielding obtained for the excited states of the alkalis.