Microwave Spectra of Molecules Exhibiting Internal Rotation. IV. Isobutane, Tertiary Butyl Fluoride, and Trimethylphospine

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Abstract
Several microwave transitions of (CH3)3CH, (CH3)3CF, and (CH3)3P have been measured and assigned. Rotational constants B0 for the three molecules are 7789.45, 4712.15, and 5816.24 Mc, respectively. Molecular structures and dipole moments have been determined. The (CH3)3CF structure indicates an unusually long CF bond. The prominent satellite lines have been assigned to excited vibrational states; the l‐type doubling pattern of transitions in degenerate states has been fitted to theory. Vibrational frequencies determined from relative intensity measurements agree with infrared and Raman results but indicate an incorrect species assignment in (CH3)3P. Frequencies of the torsional vibrations have been used to derive information of the potential function for internal rotation. The leading Fourier coefficient in this function is 3900, 4300, and 2600 cal/mole, respectively, for (CH3)3CH, (CH3)3CF, and (CH3)3P. The terms representing interactions among the CH3 groups are much smaller.