Abstract In a continuing study of the vibrational spectra of fluorinated hydrocarbons, infrared spectra have been obtained in this laboratory for several fluorinated compounds containing the CO or CCH 2 group. These compounds include 1-alkenes such as CF 3CHCH 2 1, esters such as CF 3COOCH 3 2 and CF 3COOCHCH 2 3, and most recently, 1,1,1-trifluoroacetone 4. In order to aid in making vibrational assignments for some of the compounds such as CF 3COCH 3, normal coordinate calculations have been carried out for trifluoroacetaldehyde and trifluoroacetaldehyde-d in order to obtain a force field to use as a starting point for such compounds. This force field should be reasonably transferable to trifluoroacetone or other CF 3COX compounds because the compounds differ only in the replacement of the H by CH 3 or some other group. A force field for acetone is available, which will provide initials values of force constants for the CH 3-C group 5.