The near-infrared spectrum of solid CH4

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Abstract
The infrared absorption spectrum of CH4 from 4000 to 12 000 cm−1 has been first studied in the solid phases I and II. More than forty overtone and combination bands, up to the sixth order, have been observed. Some of them are weaker by a factor of ≊105 than the infrared fundamentals. The bands have been assigned on the basis of their frequency, structure, and intensity. Features that can be attributed to propagating vibrons have been observed. The rotovibrational lines of molecules at Oh sites of phase II have been resolved in a few bands, and their relative intensities are in excellent agreement with the predictions of the extended James and Keenan model. The results reported here may help to analyze more complicated spectra, as those of CH4 in planetary atmospheres.