Correlation studies of energy gain and fragmentation in ion-fullerene collisions

Multi-ionization and fragmentation of ${\mathrm{C}}_{60}$ fullerenes induced by collisions with ${\mathrm{Ar}}^{8+}$ ions have been studied in correlation with the energy gain and the number of electrons captured and stabilized by the projectile ion. The method allows us to separate electron capture reactions from transfer ionization processes and to determine the number (r) of active electrons. When one electron is stabilized on the projectile, the target ion ${\mathrm{C}}_{60}^{r+}$ is left intact and the energy gain increases with the charge r, which ranges up to $r=4.\mathrm{}$ The corresponding mean energy gain values for production of ${\mathrm{C}}_{60}^{+}$ through ${\mathrm{C}}_{60}^{4+}$ are used together with three different models for the electronic response of ionized ${\mathrm{C}}_{60}$ in order to deduce semiempirical electron transfer distances for the first four electrons. A model with localized and mobile charges on the surface of the molecule gives a slightly better agreement with earlier measured recoil ion production cross sections than the metal sphere model or an assumption with localized charges kept fixed closest to the projectile during the collisions. The mean energy gain depends on the number of stabilized electrons s. It increases between $s=1\mathrm{}$ and 2, then it stays constant, and finally decreases between $s=5\mathrm{}$ and 6. The energy distribution for $s=6\mathrm{}$ extends to the energy-loss side, which is attributed to close collisions causing a strong electronic excitation of ${\mathrm{C}}_{60}.$