Microwave spectrum, molecular structure, barrier to internal rotation, and dipole moment of methyl monofluorogermane

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Abstract
Microwave rotational spectra of twelve isotopic species of methyl monofluorogermane (CH3GeH2F, 13CH3GeH2F, and CD3GeH2F with Ge=70Ge, 72Ge, 74Ge, and 76Ge) have been assigned in the 8 to 32 GHz frequency range. Differences in the effective moments of inertia of the 70Ge, 72Ge, and 74Ge species and information obtained from internal rotation analysis concerning the orientation of the −CH3 group with respect to the C–Ge bond axis have been utilized with the assumptions r (Ge–H) =1.525 Å and &HGeH=110° to calculate the following rs structural parameters for methyl monofluorogermane: r (C–Ge) =1.925±0.002 Å, r (C–H) =1.094±0.005 Å, r (Ge–F) =1.751±0.005 Å, &HCH=108°56′±20′, &FGeC=106°20′±20′. Analysis of ground state rotational transition splittings yield potential barriers to internal rotation of 941±20 and 921±20 cal/mole for the −CH3 and −CD3 species of the molecule, respectively. Internal rotation analyses indicate that the symmetry axes of the −CH3 and −CD3 groups are not coincident with the respective C–Ge bond axes. It has been determined that these groups are tilted toward the Ge–F bond by 1°54′±15′ and 1°51′±15′ in CH3 74GeH2F and CD3 74GeH2F, respectively. Stark effect measurements on CD3 74GeH2F yield principal axis dipole components of ‖μa‖=2.42±0.12 D, ‖μb‖=0.93±0.14 D, and a total dipole moment ‖μ‖=2.59±0.16 D, which is inclined at an angle of 23° with the Ge–F bond and an angle of 51° with the C–Ge bond.