We have made precision wavelength measurements on the 1s2s ${}_{}{}^3{}_{}{}^{}$${\mathit{S}}_1$–1s2p ${}_{}{}^3{}_{}{}^{}$${\mathit{P}}_{0,1,2}$° transitions in heliumlike boron using fast-beam laser excitation. These measurements are accurate to 2 parts in ${10}^7$ of the transition energy and test the most recent calculations at a level of 0.1% of the Lamb shift. The relatively high Z of boron, in comparison to helium, makes the transition energies sensitive to higher powers of αZ in the calculations, and our measurements show discrepancies which may be due to these uncalculated higher-order terms.

• Received 31 August 1990

DOI:https://doi.org/10.1103/PhysRevLett.66.2859