Relativistic and correlation effects cause several inversions of the triplet and singlet J = 1 levels in the 2s3p configuration of berylliumlike ions. We have studied these effects in the range of atomic number Z = 6–54 by using both relativistic and nonrelativistic multiconfiguration wave functions. Theoretical predictions of energies of these levels with respect to the 2s<sup>2</sup> <sup>1</sup>S<sub>0</sub> ground level are compared with experimental data, and we conclude that overall the predictions for the ions having Z ≥ 15 are probably more accurate than the available measurements. Calculated oscillator strengths for these resonance transitions are also reported. Near cadmium (Z = 48), we confirm still another inversion that is due to the complete dominance of relativistic effects, which was reported previously. The 2p3s (1/2,1/2)<sub>I</sub>, level, a doubly excited state, goes below the 2s3p (1/2,3/2)<sub>1</sub> level, owing to relativistic hydrogenic ordering. This type of level crossing due to hydrogenic ordering is anticipated in other sequences as well, contrary to our usual experience in atomic spectroscopy.
© 1988 Optical Society of America
Y.-K. Kim, W. C. Martin, and A. W. Weiss, "Relativistic and correlation effects in the 2s3p configuration of berylliumlike ions," J. Opt. Soc. Am. B 5, 2215-2224 (1988)