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

The Fourier transform infrared (FT-IR) specular reflection spectra from 35 alums with a general formula (MMIII)-M-I(RO4)(2). 12H(2)O were measured. Th e application of the Kramers-Kronig transformation on the reflection spectr a gives 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 resistiv ity (rho) functions are further calculated, the maxima of which give the fr equencies of the transversal optical (TO) and longitudinal optical (LO) pho nons, respectively. The LO-TO splitting for various modes varies between 0 and 60 cm(-1), depending on the oscillator strength. Reliable spectra are o btained, for the first time, for some highly efflorescent alums such as KFe (SO4)(2). 12H(2)O, RbIn(SO4)(2). 12H(2)O and NaCr(SO4)(2). 12H(2)O. (C) 199 9 Elsevier Science B.V. All rights reserved.