The IR reflectance spectra of the ν3(SO42−) and ν4(SO42−) band regions of some Tutton salts using polarized radiation: testing the model dielectric function

The investigation of the vibrational bands of the SO42− ions (in the ν3 and ν4 frequency regions) of six different Tutton salts was performed with specular IR reflectance spectroscopy using polarized radiation, on single crystal samples. The reflectance function under oblique incidence using dielectric model function as parameter (originally derived for optically uniaxial crystals) appeared to be readily applicable for the investigated monoclinic crystals. The frequencies of the transversal and longitudinal phonons were obtained by fitting of spectra recorded from (0 1 0), (0 0 1) and (1 0 0) crystal planes. Further, the symmetry types of all experimentally detected phonons were identified. Some of the results were further confirmed from IR absorption spectra recorded at liquid nitrogen temperature (LNT) of isomorphously isolated SO42− ions into the corresponding selenate matrices.