Abstract
Experiments with supersonic jet expansion have been performed to prepare clusters of benzene molecules. The clusters produced in the jet are ionized by two-photon ionization and mass analysis is achieved in a reflectron time of flight mass spectrometer. Due to an excess energy up to several hundred me V unimolecular decay occurs on a time-scale from nanoseconds up to microseconds and even longer. To discriminate against interferences from fragmentation of higher mass clusters in the observed spectra different experiments have been performed which include a new method by which single size cluster ions are stopped in the supersonic jet. These ions then stay isolated in space and the metastable decay of these complexes can be analyzed without further perturbation from fragmentation of higher clusters.