Double detachment of electrons from C2−

Cross sections have been measured for the double ionization of carbon dimer anions in collisions with rare gas atoms at impact energies in the range 20–50 keV. Both non-dissociative as well as dissociative double detachment occurs. Cross sections for the former are of the order of 3 × 10−18 cm2; they are a factor of five smaller for the latter channel. The ratio of non-dissociative to dissociative double detachment is investigated as a function of the voltage on the cathode of the Cs-vapor sputter source of anions; results indicate that carbon dimer anions are overwhelmingly produced in the ground electronic state over a wide range of operating conditions of such a source.