Far-infrared Reflection Spectra, Raman Spectra and Lattice Vibrations of CsMgCl3 and CsCaCl3

Abstract
Far-infrared reflection spectra of single crystals of CsMgCl3 and CsCaCl3 have been measured, and the frequencies of transverse and longitudinal modes of infrared active vibrations have been determined using Kramers-Kronig relation. For CsMgCl3 a measurement of polarized Raman spectra has been made. A normal coordinate analysis of the optically active lattice vibrations has been performed, in which the rigid ion model for long range Coulomb interactions and the central force field including the 1st differential coefficients of the pair-wise potential functions have been used. The obtained short range force constants K(Mg–Cl) and K(Ca–Cl) are 0.715 and 0.63 mdyn/Å, respectively, which indicate that some amount of covalent character exists in the Mg–Cl and Ca–Cl bonds.

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