Energies and fine structures of 1s22snp(n=2,3)1Poand3P2,1,0ostates of Be-like ions

The energies and wave functions of the Be-like 1${\mathit{s}}^2$2snp (n=2,3) ${}_{}{}^1{}_{}{}^{}$ ${\mathit{P}}^{\mathit{o}}$ and ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_{2,1,0}^{\mathit{o}}$ states are calculated with a full-core plus correlation method for ions from B i i to Ne v i i, Mg i x, and Si x i . 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 1${\mathit{s}}^2$2${\mathit{s}}^2$ ground state) are compared with the experiment. Intermediate coupling between the ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_1^{\mathit{o}}$ and ${}_{}{}^1{}_{}{}^{}$ ${\mathit{P}}_1^{\mathit{o}}$ states is also considered. Most of the predicted ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_{\mathit{J}}^{\mathit{o}}$ energies agree with the experiment to within a few ${\mathrm{cm}}^{\mathrm{-}1}$. The fine-structure splittings of the 1${\mathit{s}}^2$2s2p ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_{2,1,0}^{\mathit{o}}$ states calculated in this work all agree with the best experimental data in the literature. Our results show that for systems of Z≥9, it is critically important to consider intermediate coupling. For Si x i , it shifts the 2s2p ${}_{}{}^{3,1}{}_{}{}^{}$ ${\mathit{P}}_1^{\mathit{o}}$ levels by 86 ${\mathrm{cm}}^{\mathrm{-}1}$ and the 2s3p ${}_{}{}^{3,1}{}_{}{}^{}$ ${\mathit{P}}_1^{\mathit{o}}$ energies by 193 ${\mathrm{cm}}^{\mathrm{-}1}$. The predicted 2s2p