Rotational spectrum of trifluoroacetone

The rotational spectra of 5 isotopologues of 1,1,1-trifluoroacetone have been assigned using pulsed-jet Fourier-transform microwave spectroscopy. All rotational transitions appear as doublets, due to the internal rotation of the methyl group. Analysis of the tunneling splittings using both the principal axis method (PAM) and the combined axis method (CAM) methods allows to determine accurately the height of the threefold barrier to internal rotation of the methyl group, and its orientation, leading to V3 = 3.28 and 3.10 kJ mol−1, respectively. The rs geometry of the molecular skeleton, a partial r0 structure of the molecule and supporting ab initio calculations are also reported.