ENERGIES, FINE-STRUCTURES, AND ISOTOPE SHIFTS OF THE 1S(2)2SNL EXCITED-STATES OF THE BERYLLIUM ATOM

The energies and wave functions of the ls(2)2snl states of beryllium are calculated with a full-core plus correlation method. Eight excited states (2p 1,3P-degrees, 3s 1,3S, 3p 1,3P-degrees, and 3d1,3D) are studied. A restricted variational method is used to extrapolate a better nonrelativistic energy. The relativistic corrections are calculated with first-order perturbation theory. The calculated excitation energies (relative to the ground state) are compared with experiment. For the 2p 3P-degrees, 3s 1,3S, 3p 3P-degrees, and 3d 3D states, the predicted energies agree with experiment to about 1 cm-1. However, the discrepancies are larger for 2p 1P-degrees, 3p 1P-degrees, and 3d 1D. The relativistic corrections are found to be critically important in these comparisons. The predicted fine-structure splittings for 2p P-3(2,1,0)-degrees are 2.360 and 0.637 cm-1. They agree well with the 2.35 and 0.64 cm-1 in the experiment. The predicted Be-10-Be-9 2s 1S-3d1D isotope shift is 14.08 GHz. This also agrees with the 14.05(4) GHz in the experiment. The lifetime of the 1s(2)2s2p P-3(1)-degrees is calculated using the intermediate-coupling scheme.