Determination of the Rydberg Constant from the He II $n=3\mathrm{}-4$ (469-nm) Line Complex

The Rydberg constant has been determined from absolute wavelength measurements on two fine-structure components of the He II $n=3\mathrm{}-4$ transition. The He II transition was excited in a liquid-nitrogen-cooled hollow cathode. A pressure-scanned Fabry-Perot spectrometer was used to compare the He II wavelengths with a ${}_{}{}^{198}{}_{}{}^{}\mathrm{Hg}$ standard source. The measured value of the Rydberg is $R_{\infty }=109\mathrm{}737.3208\pm 0.0085$ ${\mathrm{cm}}^{-1\mathrm{}}$, where the uncertainty is one standard deviation.