ENERGIES AND FINE-STRUCTURES OF 1S(2) 2SNP (N=2,3) P-1(O) AND P-3(2,1,0)O STATES OF BE-LIKE IONS

The energies and wave functions of the Be-like 1s22snp (n=2,3) 1Po and 3P2,1,0o states are calculated with a full-core plus correlation method for ions from B ii to Ne vii, Mg ix, and Si xi. The relativistic corrections and fine structures are calculated with the first-order perturbation theory. Higher-order effects are estimated. The calculated excitation energies (relative to the 1s22s2 ground state) are compared with the experiment. Intermediate coupling between the 3P1o and 1P1o states is also considered. Most of the predicted 3PJo energies agree with the experiment to within a few cm-1. The fine-structure splittings of the 1s22s2p 3P2,1,0o states calculated in this work all agree with the best experimental data in the literature. Our results show that for systems of Z9, it is critically important to consider intermediate coupling. For Si xi, it shifts the 2s2p 3,1P1o levels by 86 cm-1 and the 2s3p 3,1P1o energies by 193 cm-1. The predicted 2s2p 1Po energies are slightly higher than the experimental data; the discrepancy increases from 14 cm-1 for Z=5 to 93 cm-1 for Z=14. © 1994 The American Physical Society.