HIGH RESOLUTION FT-IR SPECTROSCOPY OF TRANS-1.2-DIFLUOROETHYLENE
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Date
1990
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Publisher
Ohio State University
Abstract
Contrary to qualitative notions, the cis Isomer of 1,2-difluoroethylene has a lower electronic energy than the trans $Isomer.^{1}$ Consequently. calculating the energy difference and the subtle structural differences has attracted the attention of ab initlo $theorists. ^{2}$ A complete, microwave-derived structure for the cis Isomer is $available. ^{3}$ but only a partial, electron diffraction-derived structure exists for the non-polar trans $Isomer.^{4}$ With the goal of obtaining a full structure of the trans Isomer, we have begun an Investigation of the high resolution FT. IR spectra of $trans-^{1.2}$ difuoroethylene and its $-d_{1}$ and $-d_{2}$ modifications on a Bomem DA3 FT-IR spectrometer at a resolution of $0.004 cm^{-1}$. This Isomer is a near-symmetric protate rotor with $\kappa= -0,9898$. Since this molecule has $C_{2h}$ symmetry. bands are either pure type-C or hybrid type-A/B in shape. The dominant type-A component of the $\nu_{10}(b_{u})$ fundamental centered at $1274cm^{-1}$ and the type-C $v_{6}(A_{u})$ fundamental centered at $874 cm^{-1}$ have been analyzed in detail. Part of the type-B component of the hybrid band of the $v_{6} + v_{8} (Au)$ combination lone centered at $1656 cm^{-1}$ has also been analyzed. Eleven rolational parameters have been fit to 1107 ground state combination differences, derived from the three bands, with a $0.00060 cm^{-1}$. These ground state rotational parameters include $A = 1.8934058(25), B = 0.1345413(11), C = 0.1255427(10) cm^{-1}$. The significance of these results for the structure of the trans isomer will be discussed. For the type-A band, which is unperturbed, nine upper state rotational constants were list to 1052 transitions with $\sigma = 0.00060 cm^{-1}$. For this upper state, $A = 1.8926002(29), B = 0.13464887(17), C = 0.12546217(19) cm^{-1}$. The type-B and type-C bands are perturbed. A partial analysis of the latter will be discussed.
Description
$^{1}$ N. C. Craig and E. A. Entemann. J. Am. Chem. Soc. 83. 3047(1961): N. C. Craig and J. Overend. J. Chem Phys. 51 . 1127 (1969) $^{2}$ S. Saebo. and H. Sellers. J. Phys. Chem.92. 4266(1988). $^{3}$ V. W. Laurie and D. T. Pence. J. Chem. Phys. 38. 2693(1963) $^{4}$ J. L. Carios. R. R. Karl, and S. H. Bauer. J. Chem. Soc. Faraday Trans 2. 177(1974); E. J. M. van Schaick. F. C. Mijlbolt. G. Renes, and H. J. Goise. J. Mol. Struct. 21. 17(1974).
Author Institution: Department of Chemistry, Oberlin College; Molecular Physics Division, National Institute of Standards and Technology
Author Institution: Department of Chemistry, Oberlin College; Molecular Physics Division, National Institute of Standards and Technology