On the energy dependence of the yield of doubly charged negative ions during the capture of free electrons by C$_{60}$(CF$_3)_{12}$ trifluoromethylfullerene molecules

Peaks of C$_{60}$(CF$_3$)$^{2-}_{n}$ doubly charged negative ions ($n = 6$–$12$) have been observed in the mass spectra of the resonance electron capture by trifluoromethylfullerene C$_{60}$(CF$_3$)$_{12}$ molecules. It has been established that these ions are formed owing to the attachment of two free isoenergetic electrons. The autodetachment of an extra electron has been detected for the doubly charged molecular ions ($n = 12$). It has been established from the observation of the delayed fragmentation of the most abundant ions with $n = 8$ and 10 that the doubly charged negative ions, like their singly charged analogs, are metastable with respect to the separation of the CF$_3$ fragment(s). The yield of doubly charged negative ions has been obtained as a function of the electron energy. By comparing them with the analogous dependences for the singly charged ions, the specific features have been revealed which were associated with the presence of the repulsive Coulomb barrier and the regular effect of the doubled energy of two additional electrons on the energy dependence of the dissociative decay of the doubly charged negative ions. The absolute cross section for the formation of the C$_{60}$(CF$_3)^{2-}_{10}$ ions has been measured. At the energy of their yield maximum near the $5$ eV, it is $\sim1\cdot10^{-19}$ cm$^2$.