DECAY ENERGETICS OF MOLECULAR CLUSTERS STUDIED BY MULTIPHOTON MASS-SPECTROMETRY AND PULSED-FIELD THRESHOLD IONIZATION

New developments in time-of-flight mass spectrometry combined with mul ti-photon ionization provide hitherto unachievable information on the decay of weakly bound cluster ions. Dissociation thresholds of cluster ions are important for the understanding of their binding and structu re. We present two experimental methods that allow the determination o f dissociation energies of weakly bound ionic and neutral clusters. Be sides the breakdown technique observing the metastable ion efficiency curves, a novel method is presented and described which is based on de layed pulsed field ionization of long-lived Rydberg states close to th e ionization energy. In this way state-selected benzene-noble gas ions are produced and their decay is observed in a reflectron mass spectro meter. Results for dissociation thresholds of various molecular dimers and larger complexes of aromatic molecules are presented. The pronoun ced differences in dissociation energy between the neutrals and the io ns are interpreted in terms of charge-transfer resonance interaction i n the ionic complex leading to structural changes after the ionization process.