Multiple ionization of C+, N+ and O+ ions by fast electron impact

Abstract

Absolute cross sections for electron impact single and multiple ionization of C+, N+ and O+ ions leading to the formation of Cq + (q = 2–4), Nq + (q = 2–5) and Oq + (q = 2–5) are reported. The animated crossed beam method is applied in the energy range extending from the respective thresholds up to 2.5 keV. The concerned target ions belong to the second row of the periodic table, with configurations 2s22px (x = 1–3). The maximum cross sections for the multiply charged products Cq + are found to be in the range from 2.3× 10−20 cm2 (for C4 +) up to 6.3× 10−17 cm2 (for C2 +); for Nq + they range from 3.0× 10−22 cm2 (for N5 +) up to 5.1× 10−17 cm2 (for N2 +) and, lastly, for Oq + they range from 5.5× 10−22 cm2 (for O5 +) up to 5.2× 10−17 cm2 (for O2 +). The corresponding threshold energies are found to be in satisfactory agreement with spectroscopic values. The general feature of the measured cross sections is investigated. Their values for single ionization are reasonably explained by the calculations using the Coulomb–Born approximation with exchange, while those for multiple ionization are found to agree well with the semiempirical model for q = 3, but they appear to be notably overestimated by a semiempirical Bethe–Born-type formula when q > 3.