Vibrational spectrum of crystalline iodoform

The vibrational spectra of iodoform and deutero iodoform single crystals have been obtained at room temperature and liquid hydrogen temperature. The experimental data included Raman and far infrared spectra of the compound. The vibrational assignment of iodoform is discussed and the observed frequencies are compared with values calculated for k=0. Several dispersion curves along lines of symmetry in the Brillouin zone were calculated and their symmetry properties are discussed in terms of irreducible representations of space groups. Selection rules for two‐phonon transitions at critical points on the boundary of the Brillouin zone are obtained. On this basis, side bands with multiplet structure in the $\mathrm{C–H}$ stretching region are interpreted as due to combinations of the $\mathrm{C–H}$ stretching mode with lattice modes for $\mathbf{k}\text{≠ 0}$ .