Infrared Absorption Spectrum of Hydrogen Cyanide

The absorption spectrum of HCN in the gas phase has been investigated by a grating spectrometer with high resolution in the region 3μ - 15μ. Five of the infrared bands were studied, and of these the very intense fundamental at 14μ has been resolved into individual lines forming $P$, $R$ and $Q$ branches. The first harmonic of the band at 7μ has two maxima, very nearly symmetrical and equal in intensity, and no $Q$ branch. Although fine structure is indicated, it is not possible to determine the position of successive individual lines. Three other maxima, less intense and unsymmetrical are found at 4.728μ, 4.760μ, and 4.794μ forming the second harmonic of the same vibration. There is a sharp single maximum at 3.57μ with another very strong double band at 3.04μ.