Comparisons of the QED and relativistic parts of the triplet-state energies in the heliumlike sequence

We have made a careful comparison of all available high-precision data for the 1s2s ${}_{}{}^3{}_{}{}^{}$ ${\mathit{S}}_{1–}$1s2p ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_{0,1,2}$ transition energies for all nuclear charges ranging from helium (Z=2) to uranium (Z=92). Systematic discrepancies appear between theory and experiment for the J=1→0 transitions, but not for the J=1→1 and J=1→2 transitions. Analysis of laser-based high-resolution data (Z=2, 3, and 5), beam-foil spectroscopy data (Z=10–17), and hyperfine-quenched decay data (Z>27) suggests an additional contribution to the ${}_{}{}^3{}_{}{}^{}$ ${\mathit{P}}_0$ energy equal to 2.3 (Z/10${)}^4$ ${\mathrm{cm}}^{\mathrm{-}1}$.