Wavelengths of the fine structure transitions $2s{}^2{S}_{1/2}-2p{}^2{P}_{3/2}$ and $2s{}^2{S}_{1/2}-2p{}^2{P}_{1/2}$ in lithiumlike ${\mathrm{Ag}}^{44+}$ have been measured using beam-foil excitation and grazing incidence spectroscopy. The respective transition wavelengths of 40.829±0.004 Å and of 124.685±0.009 Å were not measured before for this ion. The achieved precision of 70 ppm for the 1/2-1/2 transition allows for a 0.2% QED test which sets a new benchmark in the medium Z range. Our experimental uncertainty is smaller than calculated two-photon exchange contributions to the transition energy. A summary of all published experimental data along the isoelectronic sequence for $Z>~$24, including our recent results for ${\mathrm{Ni}}^{25+}$ and ${\mathrm{Zn}}^{27+},$ is presented and compared with the best available calculations.

• Received 1 October 1998

DOI:https://doi.org/10.1103/PhysRevA.59.1874