The structure of the ionization curves of the sodium-like ions

The ionization structure of the sodium-like ions is considered. The autoionization effect, due to the excitation of the internal electrons with principal quantum number n = 2 followed by autoionization, is computed using estimated Coulomb-Born excitation cross sections. It is found that this effect is fairly large compared with the usual ionization. Results are given for Mg II, Al III, P V, Ca X and Fe XVI. The autoionization is particularly strong for the highly ionized ions of the sequence and decreases as the ions become less ionized. The limiting case of Na I is discussed.