Measurements of cross sections for detachment of electrons from C⁻and O⁻ions by electron impact

Cross sections have been measured for detachment by electron impact from C - and O - ions for interaction energies between 10 and 1000 eV. For C - the cross section attained a maximum value 1.85*10 -15 cm 2 at 18.2 eV whilst for O - the maximum value was 6.48*10 -16 cm 2 at 28.1 eV. For both ions the Bethe asymptote was reached only at energies greater than about 300 times threshold. Structure was observed in the cross section for O - at energies close to 18 eV which suggests the formation of a short-lived excited state of O 2- .