Letter | Published:

Applications of Polarimetry to Infra-Red and Micro-Wave Spectroscopy

Naturevolume 166page113 (1950) | Download Citation



G. HERZBERG and other investigators1 have recently shown that vibrational motions of homopolar molecules which should not appear in infra-red absorption give rise to absorption lines when the substance is in a condensed state (compressed gas or liquid) and when the absorption path is long enough. As the selection rules are the same as for Raman spectra, and as this absorption seems to be dependent on intermolecular forces, it seems natural to attribute it to electric moments induced in the molecules by intermolecular electric fields. The theory of electric moments induced in molecules by a macroscopic electric field can easily be derived from the classical theory of the Raman effect by substituting a constant field vector E for the vibrational field E = E0 sin 2πνt of the incident light wave, and this shows immediately that the induced absorption is governed by the same polarizability-tensor as the Raman effect. While I was developing this theory in a recent note2, my attention was directed to two papers dealing with the same subject: already in 1932 E. U. Condon3 had developed the theory of this induced absorption by electric fields on a quantum-mechanical basis, and in a recent letter in Nature, L. A. Woodward4 has pointed out that the powerful and precise methods of microwave spectroscopy could be extended to the study of pure rotational absorption of non-polar molecules.

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  1. 1

    Herzberg, G., Nature, 163, 170 (1949). Crawford, Welsh and Locke, Phys. Rev., 75, 1607 (1949); 76, 580 (1949). Oxholm, M. L., and Williams, A. D., Phys. Rev., 76, 151 (1949).

  2. 2

    Kastler, A., C.R. Acad. Sci., Paris, 230, 1596 (1950).

  3. 3

    Condon, E. U., Phys. Rev., 41, 759 (1932).

  4. 4

    Woodward, L. A., Nature, 165, 198 (1950).

  5. 5

    Kastler, A., C.R. Acad. Sci., Paris, 228, 1640 (1949).

  6. 6

    Wilson and Hull, Phys. Rev., 74, 711 (1948).

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  1. École Normale Supérieure, Paris

    • A. KASTLER


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