Rotational Spectra and Conformational Analyses of 4,4,4-Trifluorobutyric Acid and 4,4,4-Trifluorobutyric Acid-Formic Acid Complex

The pure rotational spectra of 4,4,4-trifluorobutyric acid and its complex with formic acid has been recorded in the frequency range of 7 GHz - 13 GHz. Measurements were made using a chirped-pulse Fourier transform microwave spectrometer where each target molecule was introduced in pulses of argon gas. The spectra for each molecule have been analyzed using appropriate Hamiltonians in which the parameters of the Hamiltonian have been least squares fitted to reproduce the observed rotational transition frequencies. The rotational constants are related to the moment of inertia of the molecule, which in turn provide information on the molecules’ structures. To obtain possible conformations of these molecules, B3LYP/aug-cc-pVTZ and MP2/aug-cc-pVTZ calculations were done using Gaussian. For 4,4,4-trifluorobutyric acid, forty-two a-type transitions were assigned and for the 4,4,4-trifluorobutyric acid-formic acid complex, eighty-six a-type transitions were assigned using the Pickett program. Supporting ab initio calculations, together with experimental data, have produced lowest energy conformer of the monomer and the complex, which were determined for the first time.