Electron-impact ionization ofC3+andN4+

Abstract

Measured cross sections for electron-impact ionization of ${\mathrm{C}}^{3+}$ and ${\mathrm{N}}^{4+}$ are reported for collision energies between threshold and 500 eV. The measurements were performed with crossed electron and ion beams. The peak cross sections obtained are 2.3 × ${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$ near 200 eV for ${\mathrm{C}}^{3+}$ and 1.5 × ${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$ near 400 eV for ${\mathrm{N}}^{4+}$ with good-confidence absolute uncertainties of ± 11% and ± 15%, respectively. Comparisons of present data with the available theoretical estimates range from good agreement to discrepancies of a factor of two. At the highest energies of the present measurements, near 500 eV, the cross sections have not yet begun to decrease as predicted by all the available theories. It is postulated that inner-shell-electron excitation followed by autoionization is contributing to the measured ionization cross sections at these energies. Ionization-rate coefficients are derived from the data and compared with those measured in plasmas. The agreement in ionization rates is satisfactory in the ${\mathrm{C}}^{3+}$ case, but discrepancies of nearly a factor of two exist for the ${\mathrm{N}}^{4+}$ case.