AbstractThe Raman spectra of crystalline methyl halides and the deuterated analogues were investigated at liquid nitrogen temperature. The weak band newly observed at 156 cm−1in the spectrum of CH3Cl 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−1for CH3Cl (83, 68, and 59 cm−1for CD3Cl). 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,C2νfor methyl chloride andD2hfor methyl bromide and methyl