Measurements of 2sthinsp2S1/2 endash 2pthinsp2P3/2,1/2 transition energies in lithiumlike heavy ions: Experiments and results for Ni25+ and Zn27+

Wavelengths of the fine-structure transitions 2sthinsp2S1/2 endash 2pthinsp2P3/2 and 2sthinsp2S1/2 endash 2pthinsp2P1/2 in lithiumlike Ni25+ and Zn27+ have been measured using beam-foil excitation and grazing-incidence spectroscopy. The respective transition wavelengths of 142.461±0.006thinsp Angstrom and of 216.061±0.011thinsp Angstrom for Zn27+ have not been measured so far and present the most precise values in lithiumlike heavy ions measured by beam-foil spectroscopy. The Ni25+ 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. copyright 1998 The American Physical Society