Fragmentation and ionization of C₇₀ and C₆₀ by slow ions of intermediate charge

Abstract.

We have measured total and coincident (with outgoing charge-state analyzed projectiles) ionization and fragmentation spectra of C₆₀ and C₇₀ following collisions with Xe⁴⁺ and Kr⁴⁺ at v = 0.06 a.u. Intact positive fullerene ions in charge states up to five (C₆₀ ⁵⁺ and C₇₀ ⁵⁺) are produced with both projectiles and for Kr⁴⁺+C₇₀ collisions we even observe a small C₇₀ ⁶⁺ peak. The C_60/70-2m ³⁺ (m=1–7) intensity distributions are predominantly associated with the stabilization of three electrons on the projectile (s=3) and are significantly different for Xe⁴⁺- and Kr⁴⁺-projectiles. On the other hand, we find remarkable similarities in the C₃ ⁺-C₁₁ ⁺ multi-fragmentation pattern regardless of projectile species (mass) although they are associated with closer encounters in which the projectile is fully neutralized (s=4). Simple Monte Carlo calculations of nuclear and electronic loss processes show that both these contributions are very similar in glancing Xe⁴⁺+C₆₀ and Kr⁴⁺+C₆₀ collisions, suggesting that frontal (and more violent) collisions are strongly suppressed under the present experimental conditions. Nevertheless it is surprising that the more distant collisions (s=3) are projectile mass dependent, while the closer collisions (s=4) are not. This indicates that this simple approach (although it reproduces more advanced quantum mechanical calculations for slow collisions with singly charged atomic ions rather well) is not valid for a comprehensive description of the energy transfer processes in the present collision systems involving projectiles of higher charge states.