Large amplitude motions in the electronic ground state of 4-fluoroaniline

The rotational spectra of the ground and several vibrational states of 4-fl uoroaniline, and of the ground vibrational states of the NHD and ND2 isotop omers have been measured. Most of the measured lines were split into two (0 (+) and 0(-)) components, due to amino group inversion. The potential energ y surface and the associated structural relaxation have been determined for the three lowest in energy vibrations by combining these results with ab i nitio and suitable flexible model quantum calculations.