The Molecular Spectrum of Carbon Dioxide

THE value of the specific heat of carbon dioxide indicates a triangular molecule. Bjerrum (Deutsch. Phys. Ges., 16, 737, 1914) has made a study of this molecule and has decided that the atomic nuclei lie at the corners of an isosceles triangle the apex angle of which is either 145° or 40°.6. Dennison (Phil. Mag. (7), 1, 195, 1926) decides in favour of the former angle. Such a model, according to these authors, should be characterised by three fundamental vibrational frequencies. Each tries to associate the three well-known bands of absorption at 14.66µ, 4.25µ and 2.73µ with these predicted frequencies. The model does not anticipate a fourth weak band which I found at 2.02µ (Phys. Rev., 26, 469, 1925), especially since this is not harmonic with any of the other three.