Abstract. 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.
HIGH RESOLUTION SPECTROSCOPY OF THE TWO LOWEST VIBRATIONAL STATES OF QUINOLINE C9H7N
