Three pairs of OH-stretching bands are observed at 3709 and 3701 cm-1, 3653 and 3644 cm-1, and 3628 and 3623 cm-1 in curve-fitted micro-Raman and infrared spectra of nacrite. The pairing is interpreted in terms of longitudinal (LO) and transverse (TO) modes of crystal vibrations and labelled ALO and ATO, CLO and CTO, and DLO and DTO, respectively. The relative intensities of the OH-stretching bands in the polarized micro-Raman spectrum depend strongly on both the orientation of the crystallographic axes and the direction of the electric vector of the laser beam. The inner hydroxyl bands DLO and DTO, which arise from nearly in-plane vibrations, are intense in the c(aa)c, c(bb)c and b(aa)b spectra, in which the incident laser is polarized along the crystallographic a or b axes parallel to the nacrite plates. Due to nearly out-of-plane vibrations, the inner-surface hydroxyl bands CLO and CTO, as well as ALO and ATO are intensified in the b(cc)b spectrum, where the incident laser is polarized along the c axis perpendicular to the nacrite plates.
|Number of pages||8|
|State||Published - 2001|
Bibliographical noteFunding Information:
This work was supported by The Open University of Israel Research Fund. This support is gratefully acknowledged. The assistance of Ms. Tatiana Krongaouz of the Open University of Israel is noted with appreciation.