PATTERNS AND BARRIERS FOR FISSION OF CHARGED SMALL METAL-CLUSTERS

Asymmetric fission of small doubly-charged sodium clusters, investigated via a local-spin-density molecular-dynamics method, is shown to occur predominantly via Na(n)+2 --> Na(n-3)+ + Na3+, for 4 less-than-or-equal-to n less-than-or-equal-to 1 2. For the smallest clusters (n less-than-or-equal-to 6), fission is barrierless, while fission of larger ones involves barriers. For n = 8, 10, and 12 the barriers are 0.16, 0.71, and 0.29 eV, respectively, reflecting the closed-shell stability of the parent with n = 10. The fission barriers for n > 8 exhibit a double-hump shape, and the dynamics of fission involves a precursor mechanism.