POSITIVE-ION PAIR PRODUCTION BY ELECTRON-IMPACT DISSOCIATIVE IONIZATION OF CF4

In electron impact dissociative ionization of CF4, using a time-of-flight apparatus, four cation pair coincidences have been observed between F+ ions and the fragment ions: CF3+, CF2+, CF+, and C+. Absolute cross sections and thresholds for cation pair production from the fragmentation of CF4 are reported for electron impact energies from threshold to 500 eV, with the ion pair cross sections found to contribute up to 13% to the gross ionization cross section. Also, corrections are applied to recently reported partial ionization cross section data for CF4, from which the true ion counting cross sections are computed for the first time; as well, bounds are placed on the production of neutral fluorine for electron impact energies from 20-500 eV.