Refractivities of ${\mathrm{H}}_2$, He, ${\mathrm{O}}_2$, CO, and Kr for $168\le \lambda \le 288$ nm

Precision measurements of the refractivities of ${\mathrm{H}}_2$, He, ${\mathrm{O}}_2$, CO, and Kr were made in the wavelength range 168-288 nm. By using a 1.2-m-long test cell and by keeping the test gas at accurately determined conditions near atmospheric pressure and room temperature, we were able to achieve accuracies (90% confidence limit) for the absolute refractivities that ranged from ±0.1% to ±1.0% depending upon the gas and wavelength range. For a given gas, the ratio of refractivities at any two wavelengths has a smaller uncertainty. For ${\mathrm{H}}_2$, CO, and ${\mathrm{O}}_2$, our results are for wavelengths shorter than those of previous measurements and, for He and Kr, our uncertainties are less than those of other measurements. For He our refractivities agree with the theoretical ones, but in the case of ${\mathrm{H}}_2$ our results are about 1% larger than the theoretical values. At the upper end of the wavelength range studied, our data are in agreement with previous measurements on ${\mathrm{H}}_2$, CO, and Kr. For ${\mathrm{O}}_2$ our results indicate that the hitherto available data are too large by amounts ranging from 0.8% to 10%.