PUB - Publikationen an der Universität Bielefeld

The multiple ionization and fragmentation of small polyatomic molecules and clusters, e.g. H2O, CH4, and C-60 by fast H+, He+, and Oq+ ions were studied utilizing a position-and time-sensitive multiparticle detector which allows the coincident measurement of the momenta of correlated fragments. Thereby, a kinematically complete image of the molecular break-up can be derived for each individual event. Of special interest are the "Coulomb explosion" processes, like H2O --> H++H++Oq+ where the measured dissociation energies and angular correlations show significant deviations from the pure Coulomb explosion model. For larger molecules and clusters, new phenomena may be expected. For example, using a classical molecular dynamics simulation, we have studied the break-up of hot Ar-n (n greater than or equal to 100) clusters. For initial temperatures around 500 K various analytical tools consistently indicate critical behaviour in the expansion phase.