Effect of the Atomic Core on the Nuclear Quadrupole Coupling

The effect of the electron core on the nuclear electric quadrupole coupling has been evaluated for several atomic ground states and first excited states. The antishielding produced by the $\mathrm{np}\to p$ and $\mathrm{nd}\to d$ excitations of the core is taken into account in all cases. For the ground states, the effect of the angular modes of excitation predominates, and gives a net shielding of the same order as that predicted by the Thomas-Fermi model, except for two cases of heavy atoms (Cs, W) where the antishielding predominates. For the first excited ($p$) states of the alkalis (except Li) there is a net antishielding which ranges from 10 percent for Na to 24 percent for Cs. Approximate values of the quadrupole correction factor are given for 9 atomic states.