Absolute wavelength measurement and fine-structure determination inii7

We have used collinear fast-beam–laser fluorescence spectroscopy to obtain precise measurements of the fine structures and absolute wavelengths of the 1s2s ${\mathrm{}}^3$S–1s2p ${\mathrm{}}^3$P transitions in ${}_{}{}^7{}_{}{}^{}\mathrm{i}\mathrm{i}$. Our results are about 50 times more accurate than the best nonrelativistic calculations for these energy differences, and they have a precision equivalent to 150 ppm of the QED corrections for the 2s-2p transitions.