Coulombic fission of clusters

A cluster may become not only singly, but doubly charged, and the question then arises of whether the repulsive forces set up are large enough for fission to occur. The problem is similar (but not identical in detail) to that 

In this way, a model has been developed to represent the competition between fission and fragmentation within the metallic drop approximation, analogous to that used in nuclear physics. 

Within this model, the energy change A + for the dissociation of a Z times ionised cluster containing N atoms is 

For clusters, there is no a priori relation between Z and N, except that, usually, Z N. Thus, the surface term predominates. Since the surface variation is smallest when p = 1, there is a tendency for evaporation to 

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