Raman Spectra of the Crystalline Methyl Halides

The laser-excited Raman spectra of polycrystalline CH3Cl, CH3Br, and CH3I have been measured and compared with previous infrared and Raman data. The Raman spectra are used to support certain controversial assignments of the infrared active bands and to provide additional information on the effect of the crystal field on the vibrational bands. Due to the naturally occurring isotopes of chlorine and bromine the bands assigned to the C–X stretching vibrations in the spectra of these halides are more complex than the band in the spectrum of CH3I. A model is proposed to account for the unusual contours of these bands.