Binding energy and intermolecular vibrations of neutral and ionized p-fluorotoluene•Ar cluster by mass analyzed threshold ionization

The binding energies in the neutral and ionic ground states of the p-fluorotoluene.Ar (pFT.Ar) van der Waals complex have been measured by the use of the mass analyzed threshold ionization (MATI) technique. The breakdown of the parent ion signal and the simultaneous detection of threshold ions at the fragment mass when the internal energy of the threshold cluster ion is increased above the dissociation limit are used as a probe for determining the cluster binding energy. The necessary density of vibrational bands in the vicinity of the dissociation threshold is achieved by excitation via the 9b(0)(1) band in a resonance enhanced two-photon excitation process. We find a strong Franck-Condon activity of the asymmetric bending vibrations pointing to a geometrical change of the At position along the long (chi) molecular axis because of a charge shift along this axis after ionization.