Experimental studies of fusion and fragmentation of fullerenes

Energy dependences of the fusion cross section for the collisions C⁺₆₀+C₆₀, C⁺₆₀+C₇₀ and C⁺₇₀ + C₇₀ have been measured. Fusion occurs for energies above a sharp energetic barrier V_B. The fusion barrier lies in the region between 60 and 80 eV and increases with increasing number of atoms participating in the collision. For energies beyond the barrier the fusion reaction cross section increases with collision energy to a maximum value and then decreases very rapidly. The highly excited fusion compound decays on the experimental timescale, and the resulting fragmentation pattern has been studied as a function of collision energy. For energies up to 200 eV the fragmentation behaviour can be modelled in terms of successive evaporation of C₂ units from the hot fusion product. At higher energies this model breaks down and another fragmentation mechanism has to be invoked. The overall results are in very good agreement with quantum molecular dynamics simulations and the predictions of simple phenomenological fusion models.