Jr. Durig et al., Conformational and structural studies of ethyl fluorosilane from temperature dependent FT-IR spectra of krypton solutions and ab initio calculations, J MOL STRUC, 560(1-3), 2001, pp. 39-55
The infrared spectra (3200-30 cm(-1)) of gaseous and solid ethyl fluorosila
ne, CH3CH2SiH2F, have been recorded. Additionally, the Raman spectra (3200-
30 cm(-1)) of the liquid and solid have been recorded and quantitative depo
larization values obtained. Both the gauche and trans conformers have been
identified in the fluid phases but only the gauche conformer remains in the
solid. Variable temperature (-105 to -150 degreesC) studies of the infrare
d spectra of the sample dissolved in liquid krypton have been carried out.
From these data, the enthalpy difference has been determined to be 54 +/- 1
6 cm(-1) (646 +/- 191 J/mol) with the gauche conformer the more stable form
. This is consistent with the predictions from ab initio, MP2/6-311 + G(2d,
2p), calculation as well as those with smaller basis sets with full electro
n correlations. A complete vibrational assignment is proposed for both the
trans and gauche conformers based on infrared band contours, relative inten
sities, depolarization values, and group frequencies, which are supported b
y normal-coordinate calculations utilizing the force constants from MP2/6-3
1G(d) ab initio calculations. Complete equilibrium geometries have been det
ermined for both rotamers by ab initio calculations employing a variety of
basis sets up to 6-311 + G(2d,2p) at levels of restricted Hartree-Fock (RHF
) and/or Moller Plesset to the second order (MP2) with full electron correl
ation. The adjusted r(0) parameters have been obtained for both conformers
from a combination of the previously reported rotational constants with ab
initio predicted values. All results are compared to similar quantities of
some corresponding molecules. (C) 2001 Elsevier Science B.V. All rights res
erved.