RAMAN AND INFRARED VIBRATIONAL-SPECTRA, AB-INITIO CALCULATIONS AND NORMAL-COORDINATE ANALYSES FOR 1,2-DIMETHYLTETRACHLORODISILANE AND 1,2-DIMETHYLTETRACHLORODISILANE-D(6)

The Raman spectra of CH3Cl2SiSiCl2CH3 and CD3Cl2SiSiCl2CD3 between 300 0 and 30 cm(-1) have been recorded at various temperatures. The infrar ed spectra at ambient temperature were recorded from 3000 to 50 cm(-1) . Both isotopomers exist as a mixture of gauche and anti rotamers at r oom temperature. The energy difference E-anti - E-gauche was determine d from the Raman spectra as being - 0.9 +/- 0.2 kJ mol(-1) for CH3Cl2S iSiCl2CH3 and - 1.2 +/- 0.2 kJ mol(-1) for CD3Cl2SiSiCl2CD3. Assisted by ab initio calculations, the vibrational spectra have been assigned using C-2h symmetry for the anti rotamers and C-2 symmetry for the gau che rotamers. Scaled and unsealed harmonic frequencies and harmonic sy mmetry force constants have been reported for both rotamers, and norma l coordinate analyses have been carried out. Potential energy distribu tions have been reported. (C) 1997 Elsevier Science B.V.