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The microwave spectra of SiFBr3 and CH3SiBr have been investigated in the region from 30 to 40 GHz. Assuming reasonable values for dSi-F, dSi-C and the methyl group a least squares analysis of the rotational constants yields dSi-Br ≮Br—Si—Br SiFBr3 (2,171 ± 0,001) A (111,36 ± 0,15)°, CH3SiBr3 (2,175±0,001) A (111,09±0,15)°. A barrier to internal rotation of about 1 kcal/mole is estimated by the intensity method.
The microwave spectrum of CF3CCl3 has been investigated in the region from 15 to 40 GHz. A least squares analysis of the rotational constants gave the following structural parameters: dC–C= (1,5394 ± 0,001) A, dC–F= (1,330 ±0,001) A, dC-Cl = (1,7710 ± 0,0009) A, ∢ C—C—F = (109,55 ± 0,25) °, ∢ C—C—Cl= (109,55 ± 0,25) °. The splitting of the torsional satellite may be explained by the theory of KOEHLER and DENNISON.
The microwave spectrum of several symmetric and asymmetric top isotopic species of CH3CCl3 has been studied in the region from 8 to 40 GHz. A least squares analysis of the rotational con-stants gave the following structural parameters : dC-C =(1.541 ±0.001) A, dC-Cl = (1,7712 ± 0.0008) A, dC-H = (1.090 ± 0.002) A, ∢H—C—H= (110.04±0.25) ° , ∢Cl—C—Cl= (109.39 ±0.25) °. A dipole moment of μ = (1.755 ± 0.015) D has been derived from the investigation of the Stark effect of the transition J=4→5 of CH3CCl3335. From intensity measurements the barrier to internal rotation is estimated to be (1740 ± 300) cal/mol. An analysis of the spectrum of CH2DCCl2Cl37 shows conclusively that methylchloroform in its equilibrium configuration has the methyl group staggered with respect to the CCl3-group. It could be shown that there exist two torsional isomers gauche and anti with specific microwave spectra.
The microwave spectra of SiHBr3 and SiDBr3 have been investigated in the region from 28 to 40 GHz. From the rotational constants the following structural parameters were derived by a least square method: dSi-H = (1,494 ± 0,009) A, dSi-Br = (2,170 ± 0,001) Å, ∢Br-Si-Br = (111,36 ± 0,25)0. The results are compared with those obtained for other Si-halogen-compounds.