Infrared spectra and structure of methane – noble gas mixed crystals: the influence of temperature and methane concentration on the v3 vibration band of methane

Abstract

The infrared spectra of CH4, at low concentrations in the noble gases, were obtained at temperatures ranging from 4°K up to the respective boiling points of argon, krypton, or xenon. It is concluded from this study that methane occupies substitutional cavities in these lattices. Furthermore, it is established that the potential hindering the rotation of the molecules perturbs the higher rotational levels to a greater extent than the low lying levels.In a second series of experiments, the methane concentration was varied from 0.06 to 55% for krypton; narrower ranges were used for argon and xenon. The experimental results clearly demonstrate that the influence of the CH4 concentration is different for the three systems and that the fine structure does not result from molecular aggregation.The spectrum of 0.06% CD4 in solid krypton shows fine structure which confirms the rotational origin of the four components observed for CH4. The CD4 spectra previously published were complicated with additional lines that probably arose from the nonhomogeneity of the samples.