Original scientific paper

Far Infrared and Raman Spectroscopic Investigations of the Lattice:Modes of Crystalline Thiophene

L. Colombo ; Ruđer Bošković Institute, P. O. Box: 1016, 41001 Zagreb, Yugoslavia
D. Kirin ; Ruđer Bošković Institute, P. O. Box: 1016, 41001 Zagreb, Yugoslavia
K. Furić ; Ruđer Bošković Institute, P. O. Box: 1016, 41001 Zagreb, Yugoslavia
J. F. Sullivan ; Department of Chemistry, University of South Carolina, Columbia, SC 29208, USA
J. R. Durig ; Department of Chemistry, University of South Carolina, Columbia, SC 29208, USA

Abstract

Vibrational spectroscopic measurements combined with the
lattice statics and lattice mod es calculations have been applied in
order to derive the most probable structure of the low temperature
(stable) phase V of thiophene (below 112 K). The far infrared
spectrum has been recorded from 135 to 30 cm? of this phase of
thiophene at 20 K. The low frequency Raman spectrum from
150 to 10 cm" has also been record ed for the phase V at 35 K.
From the fact that there is coincidence between lattice mode
frequencies observed in the infrared and Raman spectra, one can
exclude centrosymmetric space groups. The observations of 20
lattice modes in the Raman spectrum and 14 modes in the FIR
spectrum eliminate the possibility of tetragonal symmetry, but
the data are consistent with orthorhombic symmetry with the
unit cell containing 4 molecules on Cl sites. In spite of the
glassy-like transition observed for this phase at 42 K, both spectra
bear striking resemblance to the typical low frequency spectra
of molecular crystals. Therefore, it is assumed, for the purposes
of the static and dynamic studies, that the thiophene in phase
V can be considered as an ideally ordered crystal. Calculations
of the lattice energy and lattice mode frequencies, based on
the atom-atom potential, appear to be most consistent with
space group Pca2l (C2v5) which is in agreement with most of
the earlier predictions made for the structure of the thiophene
phase V. The Raman spectrum of the metastable phase II2 is also given.

Keywords

Hrčak ID:

175902

URI

https://hrcak.srce.hr/175902

Publication date:

30.9.1988.

Visits: 716 *