Electron impact ionization cross sections of F2 and Cl2

Total ionization cross sections for the production of positive ions by electron impact ionization of F2 and Cl2 have been measured over the energy range 12 to 100 eV. The technique involves the ionization of a modulated molecular beam with cross sections determined by measurement of a calibrant gas. Mass spectrometric measurements insured that impurities did not contribute to the measured ion currents. The 70 eV ionization cross section of F2 was found to be 1.1×10−16 cm2, and the 70 eV ionization cross section of Cl2 was 7.1×10−16 cm2.