Rotational spectra, nuclear quadrupole coupling tensors, and structures for CF3CF2X, X = Cl, Br

A chirped pulse Fourier transform microwave spectrometer was used to obtain pure rotational spectra for CF3CF2Cl between 8 GHz and 16 GHz, and for CF3CF2Br between 8 GHz and 14 GHz. In both cases rotational constants, quartic centrifugal distortion constants and chlorine/bromine nuclear electric quadrupole coupling tensors were obtained for the first time. For both compounds only the trans conformer was observed. Quantum chemical calculations have provided structures with rotational constants closely matching the experimental values. For CF3CF2Br the spectra collected were sufficiently strong that the C-13 isotopologues could be observed in natural abundance. ΔJ = 2 transitions were observed in the rotational spectrum of CF3CF2Br, but were not observed in the spectrum for CF3CF2Cl.