ABSOLUTE PARTIAL AND TOTAL ELECTRON-IMPACT-IONIZATION CROSS-SECTIONS FOR CF4 FROM THRESHOLD UP TO 500 EV

Electron-impact dissociative ionization of tetrafluoromethane (CF4) was studied with the use of a pulsed electron beam time-of-flight apparatus. The absolute partial ionization cross sections of CF3+, CF2+, CF32+, CF+, CF22+, F+, and C+ were measured from threshold up to 500 eV. The total ionization cross section was obtained by charge weighted summing of all the observed partial ionization cross sections. A total cross section for dissociation into neutral fragments was inferred from our total ionization cross section and the total dissociation cross section of Winters and Inokuti [Phys. Rev. A 25, 1420 (1982)]. The present results for the partial ionization cross sections are as much as 9% (CF3+) to 81% (F+) higher than the previously published absolute measurements of Stephan, Deutsch, and Mark [J. Chem. Phys. 83, 5712 (1985)] at 80 eV, but are in agreement with their recently revised estimates for the singly charged ions. We also found that dissociative ionization was a dominant process for electron-impact energies above 30 eV, accounting for 85% of the total dissociation cross section at 80 eV.