Negative ions produced in multicharged ions and C60 collisions

We have measured the differential cross-sections in F3+-C60 collisions at low velocity (v=0.18 a.u.). Using coincidence measurements between the ejected electron number and recoil ions, we have estimated the initial charge state of C60 parent ions associated with neutral outgoing projectiles to range from 4+ to 7+. We found that the formation of anions is correlated with the strong excitation of C60 (average excitation energy about 160 eV). The cross-section of the production of the anion has been found to be 25 a.u. This value is in agreement with the scenario of anion formation in two steps. In the first step, F3+ ions are neutralized by multicollision on the C60 surface. In the second step and at the exit part of the collision, the electron attachment process occurs. For the production of a stable anion, the capture of electrons on carbon must occur directly to the ground states of F-, giving many electron vacancies on C60. This process explains the observation of strong electronic and vibronic excitations of C60 leading to electron emission and multifragmentation processes.