Formation of doubly charged negative ions under the conditions of the resonant electron capture by fluorofullerenes

Doubly charged negative ions formed when electrons with controlled energies interact with isolated fluorinated fullerene molecules C$_{60}$F$_{n}$ ($n = 36, 48$) have been detected and investigated by resonant electron capture mass spectrometry. The dependence of the intensity of the formation of doubly charged negative ions of fluorofullerenes on the energy of attached electrons has been measured. An original method, which is based on the experimental data and does not require additional calibration quantities, has been developed for estimating the absolute cross section for the formation of doubly charged negative ions. The absolute cross sections for the formation of the most intensely formed ions C$_{60}$F$^{2-}_{36}$ and C$_{60}$F$^{2-}_{48}$ are estimated to be about $\sim 1.1\cdot10^{-24}$ and $\sim1.5\cdot10^{-24}$ m$^2$ at their maximum-yield energies of $2.0$ and $1.6$ eV, respectively.