Spectra and structure of some silicon-containing compounds Microwave and low-frequency vibrational spectra of trimethylchlorosilane

The microwave spectra of (CH ₃) ₃Si ³⁵Cl, (CH ₃) ₃Si ³⁷Cl, (CD ₃) ₃Si ³⁵Cl and (CD ₃) ₃Si ³⁷Cl have been recorded from 12.5 to 40.0 GHz. By assuming a carbon-hydrogen distance of 1.095 Å and a silicon-carbon-hydrogen angle of 110.15°, the four rotational constants were fit by a least-squares program which gave the following structural parameters: r_SiC: = 2.022; r _SiC = 1.857 Å, ∡ClSiC = 110.5°. The quadrupole splitting was resolved for the (CH ₃) ₃Si ³⁵Cl molecule and the value of -46.9 ± 1.5 was determined for the quadrupole coupling constants. The quadrupole coupling constant for (CH ₃) ₃Si ³⁷Cl was determined to be -36.5 ± 3.0 from only two resolvable components. The far-infrared spectra from 33 to 350 cm ^-1 were recorded for (CH ₃) ₃SiCl and (CD ₃) ₃SiCl in both the solid and gaseous states. The corresponding Raman spectra of the liquids and solids were also obtained. The methyl torsional modes were assigned for the solid state to bands at 233 ( e) and 208 ( a₂) cm ^-1 for the "light" molecule and at 176 ( e) and 148 ( a₂) cm ^-1 for the deuterium compound. The threefold barrier to internal rotation was calculated to have a value of 3.0 kcal/mole. Four lattice modes were observed in the far-infrared spectra and were assigned on the basis of their shift with isotopic substitution.