The polarized infra-red and Raman spectra of Mg(OH)2 and Ca(OH)2

The complete polarized infra-red and Raman spectra of single crystals of calcium and magnesium hydroxide are presented. The results are largely in disagreement with those of previous workers both with regard to frequencies and to symmetry assignments. The assignments have been confirmed by study of the spectra of the deuterated counterparts of the crystals. The implications of the results for previous calculations of the dispersion curves are stressed. It is shown that there is little mixing of rotatory and translatory character among the external modes of vibration and a discussion of the origin of the Davydov splitting of the internal modes is given. The complex combination bands observed in the infra-red absorption spectrum are discussed and compared with neutron diffraction spectra.