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The neutron powder profiles for CBr2C12 and CBrC13 have been recorded at temperatures ranging from about 260 K to 5 K. The profiles at theo highest temperatures are consistent with fcc structures with a = 8.597(2) A and a = 8.526(2) A respectively. CBrC13 has a second plastic phase observed at 245 K. The remaining profiles, below 250 K for CBr2CI2, or below 225 K for CBrC13, can be analysed in terms of the C2/c space group with 2 = 32. This is the same as for the ordered phases of CBr4 and CC14. Orientational disorder of the molecules leads to the structural similarity of all members of the family, Tests for partial ordering were not successful.

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A simple force constant model is developed and applied to the vibrations of solid sulphur dioxide. Eight parameters (two intra-and six inter-molecular force constants) are adjusted to obtain the best fit to the 15 lattice and internal mode frequencies observed by Raman and infrared spectroscopy. The calculated eigenvectors are used to assign the frequencies and to estimate the degree of translationallibrational mixing.Es wird ein einfaches Kraftkonstantenmodell entwickelt und auf die Schwingungen in festem Schwefeldioxid angewandt. Acht Parameter (zwei intra-und sechs inter-molekulare Kraftkonstanten) werden angepaBt, um beste obereinstimmung mit den 15 Gitter-und internen Schwingungsfrequenzen, die in Raman-und Infrarotspektren beobachtet wurden, zu erhalten. Die berechneten Eigenvektoren werden benutzt, um die Frequenzen zuzuordnen und den Grad der Translations-Librations-Mischung abzuschatzen.