| Abstract: | The i.r. absorption spectra sssociated with the vibrations of H? and D? ions in SrClF and BaClF have been studied in the range 600–2000cm?1.The U centers are in fluorine sites. Because of the D2d symmetry of the fluorine site, the triple degeneracy of the U center local mode in crystals of cubic symmetry, is split in BaClF and SrClF. In these crystals (space group D74h) unlike what happens with the cubic crystals, the symmetry types of the lattice band modes which give rise to the local mode sidebands, can be known experimentally. These band modes are almost only of E symmetry type. The E symmetry modes involve a vibration of the U center.A calculation of the local mode frequencies in BaClF:H? from the experimental one in BaF2:H?, has been performed. An H? ion shell model is more adequate than a rigid ion model to account for the frequencies and the relative intensities of the localized vibrational lines. The best agreement is obtained when the shell charge and the crystal polarizability of the H? ion in BaF2 are respectively ?1.3 e and 2.6 Å3. |
