Nitrogen quadrupole coupling in the microwave spectrum of trifluoronitromethane CF3NO2

Several low J microwave transitions of CF3NO2 have been measured under high resolution using a pulsed-nozzle Fourier transform spectrometer. The N-14 quadrupole coupling constants in the inertial axis system have been accurately determined as eQq(aa) = -0.641(2) MHz, eQq(bb) = 0.327(6) MHz and eQq(cc) = 0.314(6) MHz. These measurements were made in the light of renewed interest in the internal rotation dynamics of CF3NO2. The quadrupole coupling constants provide a probe of the bonding at nitrogen. The measured values are consistent with those known for CH3NO2, thus providing further evidence for an effective planar geometry of the CNO2 grouping in CF3NO2.