Precision measurement of relativistic and QED effects in heliumlike beryllium

We have used fast-ion-beam laser spectroscopy to measure the 1s2s³s-1s2p³{P}ᵒ$ intervals in Be iii to an absolute accuracy of 1 part in ${10}⁸$. Our results are (in ${cm}^{{{-}}1}): σ(1s2{s}³S₁-1s2p³{P}₀ᵒ=28 864.6120(4), σ(1s2{s}³S_1-1s2p³{P}₁ᵒ=26 853.0534(3), σ(1s2{s}³S_1-1s2p³{P}₂ᵒ$) =26 867.9484(3). These results are an improvement over previous measurements by nearly 3 orders of magnitude and show evidence of uncalculated O(${{{α}}}⁴Z⁴) relativistic corrections. Once those terms are computed, our measurement will allow QED calculations in two-electron atoms to be tested at the 100 ppm level.