The energy levels of lithiumlike bismuth are shown to be accurately described in a representation-independent manner when all diagrams involving one and two photons, with the exception of the two-loop Lamb shift, are evaluated. Comparison with the experimental value of the ${2p}_{3/2}-{2s}_{1/2}$ splitting then shows that, assuming three-photon effects are negligible, the contribution of the two-loop Lamb shift is 0.175(39) eV.

• Received 1 March 2001

DOI:https://doi.org/10.1103/PhysRevA.64.022502