Raman studies of librational motion in N2/CO and CO2/N2O mixed crystals

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Abstract
The Raman spectra of N2/CO and CO2/N2O mixed crystals have been measured in the lattice mode region. The spectra of the CO2/N2O mixed crystals exhibit very definite one‐mode behavior indicating that the librational states are within the amalgamation limit. In the N2/CO mixed crystals, the Eg and lower frequency Tg modes show one‐mode behavior while the higher frequency Tg modes show two‐mode behavior. These spectra are shown to be consistent with the established assignments and the librational exciton concept when perturbations in both the site energy and the excitation exchange interactions are considered. The effect of the random sense of the molecules in pure N2O and CO is also discussed from the librational exciton point of view. Two‐phonon scattering has been observed in all of the samples and is attributed to librational motion.