Raman spectra and crystal structures of methyl halides

Abstract

Abstract The Raman spectra of crystalline methyl halides and the deuterated analogues were investigated at liquid nitrogen temperature. The weak band newly observed at 156 cm −1 in the spectrum of CH 3 Cl has been assigned to the rotational lattice mode about the molecular symmetry axis. Three translational lattice vibrations were also found at 84, 71, and 60 cm −1 for CH 3 Cl (83, 68, and 59 cm −1 for CD 3 Cl). Of the seven and six lattice vibrations of methyl bromide and methyl iodide, respectively, two higher frequency bands were assigned to the rotational modes and the rest were assigned to the translational modes. The present experimental results are interpreted in terms of the crystal structures, C 2ν for methyl chloride and D 2 h for methyl bromide and methyl iodide.