Shell effects in fission of small doubly charged lithium clusters

The Coulombic fission of small doubly charged lithium and potassium clusters has been investigated around their critical size of stability nc=25 and nc=21, respectively. Neutral clusters are produced by the gas aggregation technique, photoionized by a pulsed laser source and mass analyzed in a tandem time-of-flight mass spectrometer. Individual fragmentation channels due to the unimolecular dissociation of size-selected parents are analyzed by using the retarding-field method. In this size range it is found that the fission has an asymmetric character. The shell effects govern the preferred output channels which include in any case the singly charged trimer. The absolute values of the fission energy barriers are estimated.