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

Four van der Waals vibrational states of the (benzene-Ar)+ cation are selectively excited by resonance-enhanced two-photon ionization and de tected with the delayed pulsed field threshold ionization technique. S election 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 o ther arguments are used to assign the van der Waals states in the neut ral and the ionic dimer. As a result a strong anharmonicity in the str etching and the bending coordinate is found.