Substituted Methanes. I. Raman and Infra-Red Spectral Data, Assignments, and Force Constants for Some Tribromomethanes

As a part of a systematic investigation of the vibrational spectra of substituted methanes and ethanes, Raman displacements, semiquantitative relative intensities, quantitative depolarization factors, and infra-red absorption frequencies in the region 700–5000 cm−1 have been obtained for CBr3H, CBr3Cl, and CBr4. Details about the design of the infra-red spectrograph are given. The Raman and infra-red spectral data in the literature for CBr3H, CBr3D, CBr3F, CBr3Cl, and CBr4 have been collected, tabulated, and critically examined in comparison with the present results and a decision was made as to the probable values of the Raman and infra-red data at the present time. Assignments of the observed Raman and infra-red bands, consistent with the selection rules, were made for all of the molecules. Finally, force constants were calculated for the five molecules, using a potential energy function containing all possible second degree terms.