An (e, 2e+ ion) study of electron-impact ionization and fragmentation of tetrafluoromethane at low energies

Abstract

We study ionization and fragmentation of tetrafluoromethane (CF4) molecule induced by electron impact at low energies (E0 = 38 and 67 eV). We use a reaction microscope combined with a pulsed photoemission electron beam for our experimental investigation. The momentum vectors of the two outgoing electrons (energies E1, E2) and one fragment ion are detected in triple coincidence (e, 2e+ ion). After dissociation, the fragment products observed are CF3+, CF2+, CF+, F+ and C+. For CF3+ and CF2+ channels, we measure the ionized orbitals binding energies, the kinetic energy (KE) of the charged fragments and the two-dimensional (2D) correlation map between binding energy (BE) and KE of the fragments. From the BE and KE spectra, we conclude which molecular orbitals contribute to particular fragmentation channels of CF4. We also measure the total ionization cross section for the formation of CF3+ and CF2+ ions as function of projectile energy. We compare our results with earlier experiments and calculations for electron-impact and photoionization. The major contribution to CF3+ formation originates from ionization of the 4t2 orbital while CF2+ is mainly formed after 3t2 orbital ionization. We also observe a weak contribution of the (4a1)−1 state for the channel CF3+.Graphical abstract