Argon-matrix-isolation Raman spectra and density functional study of 1,3-butadiene conformers |
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Authors: | Cheol Ho Choi Miklos Kertesz Sergey Dobrin Josef Michl |
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Institution: | (1) Department of Chemistry, Georgetown University, Washington, DC 20057-1227, USA, US;(2) Department of Chemistry and Biochemistry, University of Colorado, Boulder, CO 80309-0215, USA, US |
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Abstract: | s-trans, s-cis and gauche conformers of 1,3-butadiene have been studied using density functional theory and the coupled-cluster
method using double substitutions (CCD). Matrix isolation Raman and IR data for the minor conformer were obtained and are
used in combination with the theoretical results to resolve earlier ambiguities in vibrational assignments. Based on high-quality
Hessians, new harmonic stretching force constants are reported for the carbon backbone of s-trans-1,3-butadiene. For the minor conformer the best unscaled root mean square error of the calculated frequencies for the s-cis
and gauche geometries are 17.5 cm−1 and 7.4 cm−1, respectively, primarily due to a better agreement of the gauche results for the vibrations at 983 cm−1, 596 cm−1 and 470 cm−1 which depend strongly on the torsional angle. Although this points towards the gauche form rather than the s-cis form, the
calculated transition dipole moment directions at the CCD/6-311G(d,p) level confirm the earlier conclusion that the minor
conformer has C
2
v
symmetry in the matrix. It is concluded that either the better agreement between the frequencies calculated for the gauche
form and the observed values is coincidental, or that the molecule is indeed nonplanar in the matrix and tunnels very rapidly
between the two mirror-image forms (or its lowest vibrational level lies above the barrier).
Received: 1 July 1998 / Accepted: 26 October 1998 / Published online: 15 February 1999 |
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Keywords: | : 1 3-butadiene Conformers Raman spectroscopy Matrix isolation Density functional theory |
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