Lamb Shifts in Two-Electron Atoms

Abstract

From an absolute wavelength measurement of the $2s {}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}-2p {}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ transition in ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$ II we deduce a Lamb shift of 1.274±0.015 ${\mathrm{cm}}^{-1\mathrm{}}$, compared with a theoretical value of 0.99±0.04 ${\mathrm{cm}}^{-1\mathrm{}}$ for the $2s {}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ level. We suggest that the difference is due to a Lamb shift of the $2p {}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$ level and show that other measurements in isoelectronic two-electron spectra are in accord with this prediction.