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

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