| Abstract
| - The structural and conformational properties of allylgermane have been investigated using Stark and Fouriertransform microwave spectroscopies, infrared spectroscopy, and high-level quantum chemical calculations.The parent species H2CCHCH2GeH3 was investigated by microwave spectroscopy and infrared spectroscopy,while three deuterated species, namely, H2CCDCH2GeH3, H2CCHCHDGeH3, and H2CCHCH2GeD3,were studied only by infrared spectroscopy. The microwave spectra of the ground vibrational state as well asof the first excited state of the torsion vibration around the sp2−sp3 carbon−carbon bond were assigned forthe 70Ge, 72Ge, and 74Ge isotopomers of one conformer. This rotamer has an anticlinal arrangement for theCCCGe chain of atoms. The infrared spectrum of the gas in the 500−4000 cm-1 range has been assigned.No evidence of additional rotameric forms other than anticlinal was seen in the microwave and infraredspectra. Several different high-level ab initio and density functional theory calculations have been performed.These calculations indicate that a less stable form, having a synperiplanar conformation of the CCCGelink of atoms, may coexist with the anticlinal form. The energy differences between the synperiplanar andanticlinal forms were calculated to be 5.6−9.2 kJ/mol depending on the computational procedure. The bestapproximation of the equilibrium structure of the anticlinal rotamer was found in the MP2/aug-cc-pVTZcalculations. The barrier to internal rotation of the germyl group was found to be 6.561(17) kJ/mol, frommeasurements of the splitting of microwave transitions caused by tunneling of the germyl group through itsthreefold barrier.
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