Spheroidal shell model for fission of doubly charged silver clusters

Fission of doubly charged silver clusters Ag_n²⁺ is studied in the size range of 12<~n<~22. It is assumed that two fragment clusters are in contact at the transition state. The shape of each fragment is an energetically optimized spheroid. The energy barrier for various fission channels is calculated by using the shell correction method. This simple model closely reproduces the fragment size distribution measured by Katakuse et al. It is confirmed that the shell effects govern the distribution of fission fragments, while the liquid droplet model cannot explain the distribution. In particular, the even-odd oscillations observed in the distribution are found to be due to deformations of fragment clusters. Competition between fission and evaporation is discussed.