Fission channels of multiply charged sodium clusters near the Rayleigh limit

Fission of multiply charged sodium clusters Naₙq+ produced in collisions of neutral clusters with protons at 20 keV is investigated with an event-by-event acquisition technique. The analysis of fragment correlations shows that clusters undergo a strongly asymmetrical binary fission with Na⁺, Na₂⁺, Na₃⁺, Na₄⁺, and Na₅⁺ as the small fragments, Na₃⁺ dominating with approximately 70%. For a given charge q, the branching ratio of Na₃⁺ over Na⁺ emission increases with n, which is interpreted in terms of a decreasing temperature of the parent cluster following proton impact.