Distortion of the Benzene Ring in 1,2,3-Trifluorobenzene; A High-Resolution Molecular Beam Fourier Transform Microwave Study

The results of a molecular beam microwave Fourier transform study of 1,2,3-trifluorobenzene and its monosubstituted C-isotopomers, all observed in natural abundance, are presented. Typically 30 transitions were observed for each isotopomer. Centrifugal perturbation theory up to fourth order was used to analyse the observed rotational spectra. Due to the high sensitivity and resolution of the spectrometer, very accurate vibronic ground state rotational constants can be reported: They are used to derive a partial r -structure. which shows the distortions of the benzene ring caused by fluorine substitution.