Absolute partial and total electron-impact-ionization cross sections forCF4from threshold up to 500 eV

Abstract

Electron-impact dissociative ionization of tetrafluoromethane (${\mathrm{CF}}_4$) was studied with the use of a pulsed electron beam time-of-flight apparatus. The absolute partial ionization cross sections of ${\mathrm{CF}}_3^{+}$, ${\mathrm{CF}}_2^{+}$, ${\mathrm{CF}}_3^{2+}$, ${\mathrm{CF}}^{+}$, ${\mathrm{CF}}_2^{2+}$, ${\mathrm{F}}^{+}$, and ${\mathrm{C}}^{+}$ 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% (${\mathrm{CF}}_3^{+}$) to 81% (${\mathrm{F}}^{+}$) higher than the previously published absolute measurements of Stephan, Deutsch, and Märk [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.