THE VAN-DER-WAALS MODES OF THE (BENZENE-AR)+ COMPLEX STUDIED BY MASS-SELECTIVE PULSED-FIELD THRESHOLD IONIZATION

Four van der Waals vibrational states of the (benzene-Ar)+ cation are selectively excited by resonance-enhanced two-photon ionization and detected with the delayed pulsed field threshold ionization technique. Selection of different intermediate van der Waals states in the 6(1)(S1) state of the neutral benzene-Ar dimer leads basically to excitation of the same vibrational species in the ion. This propensity rule and other arguments are used to assign the van der Waals states in the neutral and the ionic dimer. As a result a strong anharmonicity in the stretching and the bending coordinate is found.