Infrared Absorption Bands of Methane

The fine structure of the infrared bands of methane in the region 1-2μ has been observed, and four new bands located at 1.135, 1.187, 1.330 and 1.734μ. The 1.66μ band observed by Moorhead was re-observed with the result that some 14 new lines were added to it. The line spacing in all the bands in this region is of the order of 10.5 ${\mathrm{cm}}^{-1\mathrm{}}$, but varies from 9.44 to 10.8 ${\mathrm{cm}}^{-1\mathrm{}}$. All the bands have sharp zero branches with a tendency to shade off on the low-frequency side, except for the one at 1.33μ, which is quite symmetrical in all its branches. The positive branch of the 1.66μ band decidedly converges to the red (line spacing increases towards the high frequencies), which was also observed by Cooley in the 3.5μ band. The infrared data in the region observed favors the tetrahedral model assumed by Dennison for theoretical work. It is possible to use as a fundamental frequency ${\nu }_1=2913\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, found in the Raman spectrum, in representing the harmonic and combination bands of methane instead of the usually assumed 4217 ${\mathrm{cm}}^{-1\mathrm{}}$ ($={\nu }_1+{\nu }_4$).