Abstract
The aim of this paper is to determine a relationship between the wavenumbers of the first OH-stretching overtones (W2νOH) and the wavenumbers of the OH-stretching fundamentals (WνOH) to help to interpret the near-infrared (NIR) spectra. The first overtone (2νOH) bands appear at wavenumbers less than twice those of the fundamental bands (νOH), due to the anharmonic character of vibrations, X = W2νOH/2 - WνOH, with X being the anharmonicity constant. Talc samples with various crystal chemistries are used to solve the equation and the experimental data are well fitted with X = −85.6 cm−1. As far as the authors are aware, it is the first time that the anharmonicity constant for the OH-stretching vibrations is determined for phyllosilicates. The anharmonicity constant remains almost unchanged for several types of clay samples. Therefore the relation, established from talc samples because their absorption bands are narrow and their wavenumber range of OH vibrations is wide, can be used for any other clay minerals.
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