Far-infrared and Raman spectra of mixed HClDCl crystals

Abstract

The far-infrared and Raman spectra of mixed hydrogen and deuterium chloride crystals in their low temperature phase have been investigated in the lattice-mode region throughout the whole concentration range. The major part of librational modes shows a delocalized mode behavior, but one librational mode exhibits a splitting characteristic of a localized mode behavior. This is explained by the small dispersion of the corresponding phonon subband. Using the results of the mixed crystal study, the proposed C 2v 12(C mc2 1 ) structure for the pure crystal has been reexamined. Good correspondences between HCl and DCl frequencies have been obtained and show, as expected, that librational modes are mixed with translational modes. Dynamic calculations made on pure HCl crystals in the orthorhombic phase are discussed. The interest of polarized light experiments is also presented, their results are used to assign frequency lines.