Ab initio calculations of vibrational properties and conformer stabilities in 1,2-Si 2H 4Cl 2, 1,1,2-Si 2H 3Cl 3 and 1,1,1-Si 2H 3Cl 3, and comparisons with observed infrared and Raman spectra
Abstract
Ab initio calculations of vibration frequencies and intensities have been made for 1,2-Si 2H 4Cl 2 (conformers 12G, 12T), 1,1,2-Si 2H 3Cl 3 (conformers 112C S, 112C 1) and 1,1,1-Si 2H 3Cl 3 ( 111), at an {HF}/{6-31 G∗} level. Energies and abundancies of both conformers have been obtained for 12 and 112 at this level, and for 12 also at {HF}/{tzvp}, {MP2 }/{6-31 G∗}{MP2 }/{tzvp} levels. Similar energies are also reported for 1,2-Si 2H 4F 2 at {HF}/{6-31 G∗} and {HF}/{tzvp} levels. A simple method of scaling the {HF}/{6-31 G∗} frequencies permits assignment of a number of bands observed in the infrared and Raman spectra of 1,2-Si 2H 4Cl 2, and of a few in infrared spectra of 112 and 111. Positions of unobserved bands are predicted to within an expected accuracy of ≈10 cm -1. The T conformer is slightly more stable than the G one in both 1,2-dichloro and 1,2-difluoro compounds, unlike the situation in the corresponding haloethanes. However, the relative stability of the 12G and 12T conformers is somewhat sensitive to basis set and level of treatment. The best estimate for the abundance X(G) of 12G is ≈0.6, in rough agreement with observed spectra. For the 112C 1 conformer, an {HF}/{6-31 G∗} calculation gives X(C 1) ≈ 0.9, a likely upper limit.
- Publication:
-
Journal of Molecular Structure
- Pub Date:
- February 1996
- DOI:
- 10.1016/0022-2860(95)09089-4
- Bibcode:
- 1996JMoSt.376..305M