The Infrared Absorption Spectrum of Formaldehyde. Part I

The infrared absorption spectrum of formaldehyde has been further investigated to beyond 11.0μ and bands were located at wave-lengths 5.7μ, 6.7μ, 7.5μ, 8.6μ and 9.6μ in addition to the regions originally reported by Salant and West and Patty and Nielsen near wave-lengths 3.5μ, 1.8μ, 1.4μ and 1.25μ. These regions of absorption were all studied under higher resolution and resolved into rotational components. The 3.5μ region. This region, originally studied by Patty and Nielsen, was remeasured and found to consist of two parallel type bands with an average spacing between lines equal to about 2.4 ${\mathrm{cm}}^{-1\mathrm{}}$, and a perpendicular type band with an average spacing of about 16.2 ${\mathrm{cm}}^{-1\mathrm{}}$. The 5.7μ region. This band was of the parallel type with its center at 5.73μ and with an average line spacing of about 2.4 ${\mathrm{cm}}^{-1\mathrm{}}$. The 6.7μ region. This band was also of the parallel type with its center at 6.65μ. Due to the bad overlapping of this region with the atmospheric water vapor bands, it was not attempted to resolve it into rotational structure. The 7.5μ region. The absorption near 7.5μ is due to a perpendicular vibration of the C${\mathrm{H}}_2$O molecule. The band shows considerable convergence, but when the spacings are averaged over an equal number of lines on either side of the center, it appears to be about 16.1 ${\mathrm{cm}}^{-1\mathrm{}}$. The 8.6μ region. The 8.6μ band is of the parallel type with its center at 8.58μ and shows an average separation between lines of about 2.4 ${\mathrm{cm}}^{-1\mathrm{}}$. It was possible also to measure this band as an emission band by heating the cell to somewhat higher temperatures. The 9.6μ region. This region was not thoroughly investigated, but a preliminary curve over this region made in emission indicates it to be of the perpendicular type with its center near 9.6μ.