Recommended data on 1snl energy levels of He-like ions (Z = 2–110)

For He-like ions, a possibility of constructing sets of recommended energy levels with reasonably estimated uncertainties has opened only recently, when high-precision calculated data appeared for the 1sns and 1snp (n ≤ 7) levels for ions with nuclear charge Z = 6–92 [1]. Earlier data of comparable accuracy were produced for n = 2 levels up to Z = 100 [2]. Published theoretical data for l = d, f, g, and h are much more fragmentary and lack any estimate of uncertainty. However, it turned out possible to evaluate the accuracy of various calculations by making isoelectronic comparisons of energy intervals between levels with the same principal quantum number n. Various interpolations and extrapolations have been used, including extrapolations along Rydberg level sequences [3]. For Z < 6, the use was made of existing accurate experimental data, as well as high-precision theoretical data for atomic He. The resulting data set includes >6000 levels. For Z > 92, it includes only the n = 2 and some of the 3p levels. Data for the 3d levels are included up to Z = 45, while higher nd levels with n ≤ 7 are included for Z ≤ 42 along with nf, ng, and nh levels with n ≤ 6. For Z > 5, these data, now included in the last release of the NIST Atomic Spectra Database (https://physics.nist.gov/asd), are much more accurate than any existing experimental data.



[1] V. A. Yerokhin and A. Surzhykov, J. Phys. Chem. Ref. Data 48, 033104 (2019)

[2] A. N. Artemyev et al., Phys. Rev. A 71, 062104 (2005)

[3] A. Kramida, Fusion Sci. Technol. 63, 313 (2013)