Microwave spectrum of the axial conformer and potential energy function of the ring puckering motion in fluorocyclobutane

The microwave spectrum of fluorocyclobutane has been investigated in the 26-40 GHz frequency range. The spectrum of the axial conformer has been assigned for the first time, while measurements of the equatorial species, and of several of its puckering vibrational satellites, have been extended. The energy of the axial conformer is 620(30) cm(-1) higher than that of the equatorial one. Previously reported potential energy functions of the ring puckering have been corrected, interpreting the available vibrational spacings, the shifts of the rotational constants upon puckering excitation and the centrifugal distortion constants with a flexible model.