Microwave spectra of mono-13C substituted acetone, (CH3)2CO

The microwave spectra of the two mono-13C isotopic forms of acetone are reported for the first time. Measurements were carried out from 11 to 25 GHz with a pulsed-beam Fourier-transform microwave spectrometer. Because overall rotation interacts with the internal rotations of the methyl groups, the spectra were analyzed with an effective rotational Hamiltonian for molecules with two periodic large-amplitude internal motions. In acetone-2-13C, the methyl groups are equivalent; in acetone-1-13C, they are not. The molecular structure has been re-examined by including rotational constant data on other isotopic forms reported previously. An equilibrium structure for acetone has been derived from the observed rotational constants and vibration-rotation constants calculated from ab initio force fields.