Vibrational spectra of hexaaqua complexes. IX. Reflection infrared spectra, optical constants and longitudinal optical phonon-transversal optical phonon splitting in some alums

摘要

The Fourier transform infrared (FT-IR) specular reflection spectra from 35 alums with a general formula M~IM~(III)(RO_4)_2 centre dot 12H_2O were measured. The application of the Kramers-Kronig transformation on the reflection spectra given the optical constants n and k which are then used to calculate the absorption spectrum and the dielectric parameters (#epsilon#_r~' and #epsilon#_r~(")). From the latter two parameters, the conductivity (#sigma#) and resistivity (#rho#) functions are further calculated, the maxima of which give the frequencies of the transversal optical (TO) and longitudinal optical (LO) phonons, respectively. The LO-TO splitting for various modes varies between 0 and 60 cm~(-1), depending on the oscillator strength. Reliable spectra are obtained, for the first time, for same highly efflorescent alums such as KFe(SO_4)_2 centre dot 12H_2O, RbIn(SO_4)_2 centre dot 12H_2O and NaCr(SO_4)_2 centre dot 12H_2O.