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 ${\mathrm{Ni}}^{25+}$ and ${\mathrm{Zn}}^{27+}$ have been measured using beam-foil excitation and grazing-incidence spectroscopy. The respective transition wavelengths of $142.461\pm 0.006\AA$ and of $216.061\pm 0.011\AA$ for ${\mathrm{Zn}}^{27+}$ have not been measured so far and present the most precise values in lithiumlike heavy ions measured by beam-foil spectroscopy. The ${\mathrm{Ni}}^{25+}$ results are in very good agreement with data from grazing-incidence spectroscopy at tokamaks. The measurement precision for both ions corresponds to less than or equal to 1% of the quantum electrodynamic contributions to the transition energies. This provides sensitivity to two-photon exchange processes for the screening of the electron self-energy.

• Received 7 May 1998

DOI:https://doi.org/10.1103/PhysRevA.58.3516