Internal Rotation of Propane from the Microwave Spectrum

The microwave spectrum of propane was observed in the first-excited states of the CH3torsion. Each transition was split into a symmetric triplet; the splittings were 14–19% larger for the (−) state than for the (+) state. The top-top interaction and its effect on the rotational spectra were treated by the perturbation theory, and the results were applied to the analysis of the triplet splittings. The two barrier parameters, V3 and V3″, were thus determined to be 3325±20 and −170±30 cal/mol respectively.