Wavelengths of the fine-structure transition $2s{}^2{S}_{1/2}$–$2p{}^2{P}_{1/2}$ in lithiumlike ${\mathrm{Sn}}^{47+}$ and ${\mathrm{Xe}}^{51+}$ have been determined using beam foil excitation and grazing incidence spectroscopy. Transition wavelengths of $114.895\pm 0.008\hspace{0.5em}\AA$ for ${\mathrm{Sn}}^{47+}$ and $103.475\pm 0.007\hspace{0.5em}\AA$ for ${\mathrm{Xe}}^{51+}$ have been measured. While there has been no previous measurement of this transition in Sn, the Xe result marks an improvement in accuracy of more than an order of magnitude compared with previous experiments. The achieved precision of 70 ppm for the 1/2-1/2 transition allows for a 0.1% QED test which establishes a new benchmark for Li-like ions in the medium Z range. The experimental uncertainty is smaller than the size of the smallest calculated contribution to the transition energy.

• Received 20 August 1999

DOI:https://doi.org/10.1103/PhysRevA.62.022501