Balan E., Fritsch Emmanuel, Juillot Farid, Allard T., Petit S. (2021). Local mode interpretation of the OH overtone spectrum of 1 : 1 phyllosilicates. European Journal of Mineralogy, 33 (2), p. 209-220. ISSN 0935-1221.
Titre du document
Local mode interpretation of the OH overtone spectrum of 1 : 1 phyllosilicates
Balan E., Fritsch Emmanuel, Juillot Farid, Allard T., Petit S.
Source
European Journal of Mineralogy, 2021,
33 (2), p. 209-220 ISSN 0935-1221
Although OH overtone bands of 1 : 1 phyllosilicates are commonly observed in their near-infrared (NIR) spectra, their interpretation in terms of transitions between specific vibrational states is still uncertain. This situation can be traced back to the coupled nature of the fundamental OH-stretching modes involving the interlayer OH groups of 1 : 1 phyllosilicates. In this case, the overtone spectra cannot be directly related to their fundamental counterparts observed in the mid-infrared (MIR) spectra. In the present study, we use a parameterized quantum-mechanical approach to compute the vibrational frequencies related to the fundamental and overtone bands in serpentine group and kaolinite group minerals. The simple model is based on a description of the vibrational properties of a cluster of OH groups in terms of harmonically coupled anharmonic oscillators. The comparison of the theoretical results with experimental observations makes it possible to interpret most of the salient features of the overtone spectrum of 1 : 1 phyllosilicates. Unlike the bands observed in the MIR spectra, the overtone bands observed between 7000 and 7300 cm(-1) are related to local transitions from the ground state to the second excitation level of OH groups, whereas the weaker bands observed between 7300 and 7400 cm(-1) involve a double excitation to the first vibrational level of OH oscillators. The results also support the assignment of specific overtone bands to the occurrence of substituted divalent cations of transition elements in serpentine group minerals.
Plan de classement
Sciences fondamentales / Techniques d'analyse et de recherche [020]
;
Géologie et formations superficielles [064]
