Refractive Indices of the Condensed Inert Gases

The refractive indices of condensed argon, krypton, and xenon have been measured for wavelengths between 3612 and 6439 Å by the spectroscopic method of minimum deviation. The Lorentz-Lorenz functions $f_{\mathrm{LL}}$ are found to remain constant to within about 3% over the entire range studied, with a small decrease (∼1%) on freezing. At higher solid densities, the $f_{\mathrm{LL}}$ functions decrease with increasing density at an accelerating rate. This behavior is in moderate agreement only with theoretical predictions based on the tight-binding exciton model.