Evidence for Coulomb Explosion of Doubly Charged Microclusters

Mass spectra of Pb, NaI, and Xe microclusters show that below a critical number of atoms per cluster, n**, doubly charged particles are not stable. These numbers are 30 for Pb„, 20 for {NaI)„and 52 for Xe„. The two positive charges generated at one atom by electron bombardment are likely to move to opposite sides of the cluster which then explodes into singly charged fragments as long as the Coulomb repulsion energy is greater than the binding energy.