Fragmentation of Bi clusters by multiply charged ions

We report on collisions of multiply charged ions with free Bi nanoparticles in the gas phase. The nanoparticles contain up to 650 Bi atoms corresponding to a diameter of 3.5 nm. The stability limit of multiply charged Bi clusters has been investigated yielding appearance sizes for Bi clusters in charge states up to q = 6, which are in good agreement with predictions of the liquid drop model. This finding underlines the metallic character of the Bi particles. By coincidence measurements the correlation between the dominant fragments Bi+ and Bi-3(+) and larger multiply charged residues has been determined. The comparison of the kinetic energies with Q-value calculations within the liquid drop model allowed identifying specific decay processes as two-body asymmetric fission or multifragmentation events. The higher kinetic energies of singly charged monomer ions compared to that of trimer ions are explained by a higher fissility of the decaying system. Correlation islands for small fragments indicate different decay mechanisms based on two-step processes where a third undetected fragment can be emitted in the first or the second step.