Absolute partial and total electron impact ionization cross sections for CF4 from threshold up to 180 eV

Abstract

Electron impact ionization of carbon tetrafluoride was studied as a function of electron energy from threshold up to 180 eV. A double focusing mass spectrometer system with an improved electron impact ion source was used, alleviating the problems of ion extraction from the source and the transmission of the extracted ions through the mass spectrometer system. Absolute partial ionization cross section functions for the production of CF+3, CF+2, CF+, C+, F+, CF2+3, and CF2+2 in CF4 have been determined. In addition, the total (and the counting) ionization cross section function of CF4 has been determined (summation method) and is compared with calculations based on classical and semiclassical binary encounter approximations. Using nth root extrapolation ionization energies of the following doubly charged fragment ions have been derived: AE (CF2+3) =41.8±0.3 eV, AE (CF2+2) =42.9±0.3 eV, and AE (CF2+)=52.1±0.5 eV. In accordance with previous results no stable CF+4 parent ion has been detected, however, a metastable dissociation process CF+*4→ CF+3+F has been observed.