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Characteristics of Low-Frequency Molecular Phonon Modes Studied by THz Spectroscopy and Solid-State ab Initio Theory: Polymorphs I and III of Diflunisal

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journal contribution
posted on 25.01.2016, 00:00 by Feng Zhang, Houng-Wei Wang, Keisuke Tominaga, Michitoshi Hayashi
THz absorption spectra of two polymorphs of diflunisal, form I and form III, exhibit distinct features due to the influence of packing conformations on the frequency distributions and IR activities of gamma point phonon modes within the 100 cm–1 region. In order to understand the origins of these THz modes, we perform a detailed mode analysis. The result shows that although the spectral features are different, these low-frequency phonon modes of the two molecular polymorphs have similar vibrational characteristics in terms of harmonic couplings of intermolecular and intramolecular vibrations.