Accession Number : AD0699019

Title :   OPTICAL SPECTRA OF ORIENTATIONALLY DISORDERED CRYSTALS. III. INFRARED SPECTRA OF THE SOUND WAVES,

Corporate Author : NATIONAL RESEARCH COUNCIL OF CANADA OTTAWA (ONTARIO) DIV OF APPLIED CHEMISTRY

Personal Author(s) : Whalley,E. ; Labbe,H. J.

Report Date : 29 JAN 1969

Pagination or Media Count : 8

Abstract : The theory of the absorption of light by the translational vibrations of orientationally disordered crystals has been extended to low frequencies where the vibrations are short-wavelength sound waves whose density of states can be represented by the Debye model. Both the integrated intensity of a normal vibration and the density of states are proportional to the frequency squared, so the absorptivity is proportional to the fourth power of the frequency. The absorptivity of ice has been measured below/45 cm in order to test the theory. As predicted, it is approximately proportional to the fourth power of the wavenumber. At low frequencies the absorptivity becomes approximately proportional to the square of the wavenumber and is probably caused by two-phonon difference bands involving high-frequency acoustic phonons. The microwave absorptivity reported by others appears to be consistent, at least approximately, with this square line extrapolated, which suggests that it also is due mainly to two-phonon difference bands. The absorptivity is less than predicted due to two approximations in the theory. (Author)

Descriptors :   (*ICE, *INFRARED SPECTRA), (*INFRARED RADIATION, *SOUND), (*CRYSTAL LATTICES, INFRARED SPECTRA), VIBRATION, PHONONS, BAND SPECTRA, CANADA

Subject Categories : Crystallography
      Atomic and Molecular Physics and Spectroscopy
      Solid State Physics

Distribution Statement : APPROVED FOR PUBLIC RELEASE