Infra-red investigations of molecular structure.-Part III. The molecule of carbon monoxide

Abstract

Although the infra-red bands of carbon monoxide have been known for years, they have not yet been resolved. In 1913 Burmeister found, among the many doublets which he measured, one due to CO with its centre at 4·66 μ, and from the Rayleigh-Bjerrum separation an approximation to the moment of inertia was made. The harmonic at 2·35 μ was observed by Brinsmade and Kemble in 1917 ; Schaefer and Thomas added a second harmonic, at 1·2 μ, to the known bands ; E. F. Lowry in 1924 tried to analyse Burmeister's doublet into the rotational fine structure which it must be supposed to have, but had no success. There has been some theoretical speculation based upon the scanty data of the vibration bands. Hettner* in 1920 showed the frequency relationships of the bands found by Burmeister and by Brinsraade and Kemble could be explained by the assumption that the 2·35 μ. band was an overtone of the 4·66 μ band (in the paper published later in the same year which is the foundation of our theoretical knowledge of vibration-rotation spectra. Kratzer did not include these frequencies as an example of the anharmony which lie was able to prove for other molecules). Dennison compared the observed intensity ratios with a ratio calculated from a very rough approximation. The molecule has generally been assumed HCl-like, but for confirmation theory had to wait upon experiment.