Comparison of Theoretical and Experimental Level Values of the<i>n</i>= 2 Complex in Ions Isoelectronic with Li, Be, O and F

Abstract

The differences between observed and theoretical values of level intervals within the n = 2 complex in ions isoelectronic with Li, Be, O and F have been studied as functions of Z. The theoretical values are based on the tables of Cheng, Kim and Desclaux. For spin-orbit intervals, σ (theor) is taken as their multiconfiguration Dirac-Fock value with Breit correction (MCDF + B), for other intervals within the same configuration the Z-independent correlation energy from Cheng, Froese Fischer and Kim is added, and for interconfiguration intervals a Lamb-shift correction is also included, obtained by transforming the values of Cheng et al. into a smooth function of Z. The difference σ (obs) - σ (theor) is then expressed by the formula A + B(Z - C)-1 + a(Z - s)x, where the first two terms account for the residual correlation energy and the last term comprises all additional relativistic and radiative corrections. In a few cases we had to use two such terms with opposite sign and exponents differing by 2 to 3 units. The constants A, B, C, a and x are adjusted to fit the observations within their error limits. As compared to a fitted polynomial, the present formula is much better suited for extrapolation and provides a sharper test of the experimental data, especially at the high-Z end of a sequence. It has revealed a number of incorrect line identifications in the Be sequence. The results of the analyses are summarized in tables of recommended level values and wavelengths, extending to Z = 36 and in some cases to Z = 42. The wavelengths obtained for the resonance lines in the Be, O and F sequences may become useful as wavelength standards.