Excitation and fragmentation of ${\mathrm{C}}_{60}^{r+}$ $(r=3\mathrm{}–9)$ in ${\mathrm{Xe}}^{30+}{-\mathrm{C}}_{60}$ collisions

We have measured the branching ratios between ${\mathrm{C}}_2$ evaporation, asymmetrical fission, and multifragmentation of ${\mathrm{C}}_{60}^{r+}$ $(r=3\mathrm{}–9)$ in ${\mathrm{Xe}}^{30+}{-\mathrm{C}}_{60}$ collisions at 300 keV impact energy $(v=0.3\mathrm{}\mathrm{a}.\mathrm{u}.\mathrm{}).\mathrm{}$ By multifragmentation we mean here a complete destruction of the ${\mathrm{C}}_{60}$ cage leading to observation of rings and linear chains. The fragmentation ratio, equal to the number of unstable ${\mathrm{C}}_{60}^{r+}$ divided by the sum of stable and unstable parent ions, has been found to increase from 0.3% to 97% for ${\mathrm{C}}_{60}^{3+}$ to ${\mathrm{C}}_{60}^{9+}$ ions. From these measurements, the internal excitation energy has been estimated to be about 75 eV, slightly increasing from ${\mathrm{C}}_{60}^{3+}$ to ${\mathrm{C}}_{60}^{5+}$ ion. The multifragmentation process has been found dominant for ${\mathrm{C}}_{60}^{(7\mathrm{}–9)+}.$ The asymmetrical fission process has been observed for fullerene ions up to ${\mathrm{C}}_{60}^{9+}$ showing that, in these collisions, ${\mathrm{C}}_{60}$ ions can be produced at very low-internal energy. The “phase transition” associated with the multifragmentation process is observed starting with ${\mathrm{C}}_{60}^{6+}$ ions.