Born-approximation electron ionization cross sections forAln+ (0≤n≤11)and some ions of the Na isoelectronic sequence

Abstract

Generalized oscillator strengths (GOS) for excitation and ionization of all occupied shells of ${\mathrm{Al}}^{n+} \left(0\mathrm{}\le n\le 11\right)$, and the Mg, Si, Ni, and Zn ions of the sodium isoelectronic sequence were calculated. The Al-ion GOS were used elsewhere to compute proton stopping power. There were no measurements or other calculations on stopping power with which to compare our calculations. Here the Al-ion GOS are used to calculate electron-ion ionization cross sections, including the effects of excitation followed by autoionization. The cross sections agree to 20% or better with measurements and other calculations, except near threshold. Calculations are also performed for five ions of the Na isoelectronic sequence to examine the relative importance of direct ionization versus excitation followed by autoionization. Comparison with recent measurements on three of these ions (${\mathrm{Mg}}^{1+}$, ${\mathrm{Al}}^{2+}$, and ${\mathrm{Si}}^{3+}$) shows agreement to better than 10% in some cases, and no worse than 20% in any case.