Hydroxyl-stretching bands in curve-fitted micro-Raman, photoacoustic and transmission infrared spectra of dickite from St. Claire, Pennsylvania

The OH-stretching region in curve-fitted micro-Raman, photoacoustic and tra nsmission IR spectra of St. Claire dickite was investigated. Polarized Rama n spectra recorded from the (001) and (010) faces of the dickite crystal di splayed six prominent OH bands. The relative intensities depend strongly on both the orientation of the crystallographic axes and the direction of the electric vector of the laser beam. Four out-of-plane vibrations, A(A), A(Z ), C-A and C-Z, at similar to 3710, 3706, 3654 and 3643 cm(-1) respectively , predominate when the electric vector is perpendicular to the dickite plat es. Two in-plane vibrations, D-Z and D-A at 3627 and 3623 cm(-1), intensify when the electric vector is parallel to the plane. The relationship betwee n band intensity and crystal orientation was interpreted in terms of longit udinal optic (LO) and transverse optic (TO) crystal vibration modes. These LO and TO crystal modes were also observed in curve-fitted photoacoustic an d transmission IR spectra of coarse, non-oriented crystals of the dickite.