Some Molecular Absorption Spectra of Hydrogen Cyanide

Infra-red absorption maxima due to hydrogen cyanide.—Four of the infrared bands due to HCN have been associated by Kratzer as fundamental and successive harmonics. Of these, the fundamental at 14μ can not be reached with the grating spectrometer at present, but the three others have been examined with specially ruled gratings giving higher dispersion than was previously employed. Two maxima, very nearly symmetrical and of equal intensity, appear at 6.94μ and 7.23μ. Three others, less intense and unsymmetrical, are found at 4.756μ, 4.723μ and 4.79μ. There is a sharp single maximum at 3.564μ. The forms of the curves and the separations between maxima raise some doubts as to whether the higher frequency bands are second and third harmonics of the one at 14μ. If they are, it appears that the intensity of the zero branch increases with the order of the vibrational transition. The band series could not be resolved. Estimates of the moment of inertia of the molecule from various bands do not agree. The measurements at 7μ give about 13.2×${10}^{-40\mathrm{}}$, which is five times that of HCl.