The orientation determination of OH⁻ dipoles in staurolite by polarized infrared spectroscopy

Abstract

Polarized infrared absorbance spectra from the oriented plates of staurolite were examined for the orientation determination of OH⁻ dipoles in staurolite by a Fourier transform polarized infrared absorbance spectroscopy (pol-mFTIR). Seven polarized absorbance spectra observed in 3 μm region are due to the OH⁻ dipoles essentially existing in staurolite structure, and all of the corresponding OH⁻ dipoles are oriented parallel to the (010) plane. Three of the seven absorbance spectra are assigned to OH⁻ dipoles due to two sets of the OH bonds, P(1A)–O(1A) and P(1B)–O(1B), and P(2A)–O(1A) and P(2B)–O(1B), directly found by neutron diffraction studies. Unassigned four absorbance spectra indicate that additional hydrogen positions must be present in staurolite, and the unidentified hydrogen may be estimated to be a considerable quantity.