Electron capture and ionization phenomena in SF₆and C₇F₁₄

Using an ionization chamber of the Lozier pattern, modified to include a retarding potential difference beam analyser as used by Fox et al. in 1951, measurements have been made of the ionization and attachment cross sections in SF6 and C7F14 in single-collision conditions. These gases are of interest in connection with studies of gases of relatively high dielectric strength. Particular attention was paid to the attachment cross sections for electron energies below 1 ev; the maximum values were found to be of the order of 10-15 cm2 for SF6 and 10-14 cm2 for C7F14. The main attachment takes place in a resonance process within a very small range (less than 1 ev) of electron energies. The ionization cross section data do not reveal any features of special interest, although in SF6 the ionization current/electron energy curve shows several inflections, some of which can be attributed to known dissociation and ionization processes.