FAR-INFRARED SPECTRA AND BARRIERS TO INTERNAL-ROTATION FOR THE CF3CXO MOLECULES WHERE X = H, F, CL, BR, CH3 AND CF3

The far-infrared spectra (350-30 cm-1) of CF3CHO,CF3CFO, CF3CClO, CF3CBrO, CF3CO(CH3) and (CF3)2CO have been recorded at a resolution of 0.10 cm-1. The torsional fundamentals for the CF3 rotors have been assigned at 66.2, 45.6, 41.8, 38.3, 36.1 and 53.8 (39.0) cm-1, respectively, where two frequencies are observed or the CF3 torsional modes of (CF3)2CO, and each fundamental for all of the molecules has several accompanying "hot bands". Utilizing these torsional data, along with reasonable structural parameters to calculate the kinetic constants, the periodic barriers to internal rotation have been determined. The barrier values for the CF3 rotors with the statistical uncertainties are 292+/-5, 381+/-1, 434+/-2, 429+/-2, 295+/-1, and 777+/-5 cm-1 for these CF3CXO molecules, where X = H, F, Cl, Br, CH3 and CF3, respectively. These results are compared to the methyl barriers in the corresponding series CH3CXO.