Investigation of Davydov Splitting in the ir Spectra of Crystalline Dicarboxylic Acids

Author(s) S.I. Kshnyakina1, Yu.M. Lopatkin1, T.A. Havrilko2
Affiliations

1 Sumy State University, 2, Rimsky-Korsakov Str., 40007, Sumy, Ukraine

2 Institute of Physics NASU, 46, Nauky Av., 680028, Kyiv, Ukraine

Е-mail yu.Lopatkin@meta.ua, SKshniak@yandex.ru
Issue Volume 1, Year 2009, Number 3
Dates Received 02.11.2009, in final form 09.12.2009
Citation S.I. Kshnyakina, Yu.M. Lopatkin, T.A. Havrilko, J. Nano- Electron. Phys. 1 No3, 37 (2009)
DOI
PACS Number(s) 71.70 – d, 78.30. – j, 78.30.Jw
Key words Davydov splitting, Dicarboxylic acids, IR spectra, Normal modes, Absorption (15) .
Annotation
In the present paper the collective (vibrational) excitations in molecular crystals were studied. Since the corresponding molecular interactions are characterized by a small radius, the investigation results are important for the molecular and nanoelectronics problem solving.
The paper includes the investigation results of resonance (Davydov) splitting of the methylene СН2 group rocking vibrations in the IR absorption spectra of even homologues of crystalline dicarboxylic НООС(СН2)nСООН acids (crystal space group P21/a). Temperature dependence of the Davydov splitting value for the series of rocking vibration bands of methylene groups in the spectral range 700-1100 cm–1 was investigated for homologues with the number of carbon atoms n = 4-10 using the polarized IR spectroscopy in the wide temperature range 100-300 K. Interpretation of the series of rocking vibration bands of methylene groups in the IR absorption spectra of even homologues of crystalline dicarboxylic acids is performed. Based on the theoretical calculation of normal modes and the assignment of observed absorption bands to vibrations of different symmetry types it was shown, that in the spectra of the studied acids the series of rocking vibration bands may be interpreted as the vibration of (n – 2) methylene groups connected by the collective interaction, in contrast to the case of normal paraffins where all the methylene groups are involved in rocking vibrations. Dependence of the Davydov splitting value on the number of methylene groups is analyzed, and shown that this value increases proportionally to the methylene chain length.

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