Single and multiple ionization of ${\mathrm{C}}_{60}$ fullerenes and collective effects in collisions with highly charged C, F, and Si ions with energy 3 MeV/u

We have measured absolute cross sections for single, double, triple, and quadruple ionization of ${\mathrm{C}}_{60}$ in collisions with 3 MeV/u C, F, and Si projectile ions at various projectile charge states. The experiment was performed using the recoil-ion time-of-flight technique. Projectile charge state dependence of the ionization yields was compared mainly with a model based on the giant dipole plasmon resonance (GDPR). In some cases, the continuum-distorted-wave–eikonal-initial-state (CDW-EIS) model which is normally applied for ion-atom collisions was also used as a reference. An excellent qualitative agreement between the experimental data for single and double ionization and the GDPR model predictions was found for all projectile charge states.

Figure 1

Schematic drawing of the TOF mass spectrometer.

Figure 2

TOF mass spectrum of the recoil ions showing the single and multiple ionization and fragmentation products of ${\mathrm{C}}_{60}$ in collisions with for 3 MeV/u ${\mathrm{C}}^{6+}$ ions. The TOF of the recoil ions has been converted to their mass-to-charge ratio ($x$ axis). The mass peaks are not corrected for MCP detection efficiency. Also visible in the spectrum are the peaks corresponding to ${\mathrm{N}}_2$ and ${\mathrm{H}}_2$O present in the background gas.

Figure 3

Same TOF spectrum as in the Fig. 2, corrected for MCP detection efficiency.

Figure 4

Expanded view of low mass region in Fig. 3. Singly ionized ${\mathrm{C}}_n\hspace{0.5em}{}^{1+}$ cluster ions can be seen for $n=1$ to 12. Inset in the figure shows peculiar structure of ${\mathrm{C}}_2\hspace{0.5em}{}^{1+}$ fragment ion peak observed in the experiment.

Figure 5

Absolute ionization cross sections for (a) single, (b) double, (c) triple, and (d) quadruple ionization of ${\mathrm{C}}_{60}$ in collisions with 3 MeV/u C, F, and Si projectiles. Solid lines show the respective GDPR predictions. The GDPR curve is normalized to the experimental data at $12+$ projectile charge state in each case, and the respective normalization factors are as follows (a) 1.9, (b) 1.9, (c) 1, and (d) 0.22.

Figure 6

Absolute single-ionization cross sections for ${\mathrm{C}}_{60}$ in collisions with 3 MeV/u C, F, and Si projectile ions. Open symbols show the experimental data. The solid line represents the normalized GDPR cross sections (see caption for Fig. 5). The dotted line shows the single-ionization cross sections calculated using CDW-EIS calculations for a carbon target modified appropriately to include the electron density of ${\mathrm{C}}_{60}$.