Molecular spectra in the extreme infra-red

Abstract

The appearance in the spectrum of monochromatic light diffused by fluids, of new lines of modified frequency (Ind. Jour. Phys., vol. 2, pp. 387 and 399; 1928), gives us a powerful, accurate, and convenient method of exploring molecular spectra, especially in the near and extreme infra-red regions. We have only to photograph the spectrum of the scattered light, and the frequency-differences between the incident light and the new radiations excited by it give us the molecular frequencies. As an illustration of what the method is capable of, we may mention the case of carbon tetrachloride, the spectrum of the mercury arc scattered by which is reproduced as Fig. 1 B, 1 A being the incident spectrum. The 4358 A. line, which is the principal exciter, is accompanied by three sharp lines close to it on the right, from which we deduce 45.4 Î1/4, 31.8 Î1/4, and 21.7 Î1/4 as wave-lengths of three hitherto unknown infra-red lines in the spectrum of the carbon tetrachloride molecule. In addition, we have a doublet 13.0 Î1/4. and 12.6 Î1/4, the position of which as an unresolved line was approximately known from the work of Coblentz.