Regular Article

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

¹ Max Planck Institute for Nuclear Physics, 69117 Heidelberg, Germany
² University of Santiago de Compostela (USC), 15782 Santiago de Compostela, Spain
³ Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India

^a e-mail: alexander.dorn@mpi-hd.mpg.de

Received: 20 October 2017
Received in final form: 21 December 2017
Published online: 8 March 2018

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⁺.