Electron-impact ionization of the C2F5free radical

We measured absolute cross sections for the electron-impact ionization and dissociative ionization of the C 2 F 5 free radical from threshold to 200 eV using the fast-neutral-beam technique. The electron-impact ionization of C 2 F 5 is dominated by two channels, the formation of the CF 3 + fragment ion which has the largest partial ionization cross section with a value of 3.5 × 10 -16 cm 2 at 70 eV and the formation of the C 2 F 5 + parent ion with a cross section of 1.3 × 10 -16 cm 2 at 70 eV. Both partial cross sections have error margins of about ±15%. All other partial ionization cross sections have maximum cross section values of less than 0.1 × 10 -16 cm 2 . The total single C 2 F 5 ionization cross sections at 70 eV (derived from the two measured partial ionization cross sections and an estimate for the sum of the cross sections for all weaker, unobserved ionization processes) was found to be about 5 × 10 -16 cm 2 . A comparison of the measured total single-ionization cross sections with a calculated cross section, using a modified additivity rule, shows good agreement up to an electron energy of 50 eV, but poor agreement at higher impact energies. This behaviour is somewhat similar to that observed for the CF x ( x = 1-3) free radicals, but it is very different from the excellent agreement between the calculated and measured total single-ionization cross sections that was observed for the stable molecules CF 4 and C 2 F 6 .