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 1s(2)2snp (n=2,3) P-1(o ) and P-3(2,1,0)o, states are calculated with a full-core plus correla tion. method for ions from B II to Ne VII, Mg IX, and Si XI. The relat ivistic corrections and fine structures are calculated with the first- order perturbation theory. Higher-order effects are estimated. The cal culated excitation energies (relative to the 1s(2)2s(2) ground state) are compared with the experiment. Intermediate coupling between the P- 3(1)o and P-1(1)o states is also considered. Most of the predicted P-3 (J)o energies agree with the experiment to within a few cm(-1). The fi ne-structure splittings of the 1s(2)2s2p(3)P(2,1,0)(o) states calculat ed in this work all agree with the best experimental data in the liter ature. Our results show that for systems of Z greater than or equal to 9, it is critically important to consider intermediate coupling. For Si XI, it shifts the 2s2p(3,1)P(1)(o) levels by 86 cm(-1) and the 2s3p (3,1)P(1)(o) energies by 193 cm(-1). The predicted 2s2p(1)P(o) energie s are slightly higher than the experimental data; the discrepancy incr eases from 14 cm(-1) for Z=5 to 93 cm(-1) for Z=14.