A determination of the refractive indices of thin films of oxygen, nitrogen, carbon dioxide, water, argon, neon, and krypton condensed at 4.2 °K was made. These were obtained for the 5461 A line of Hg with an ellipsometer. Similar measurements were also made on films of these gases condensed after passage through a microwave discharge. With the exception of N2 and Kr, measurable differences in refractive indices were observed between films condensed from discharged and undischarged gases.
J. KRUGER and W. J. AMBS, "Optical Measurements on Thin Films of Condensed Gases at Low Temperatures," J. Opt. Soc. Am. 49, 1195-1198 (1959)