Collision-Strength Shift in Electron-Impact Single and Double Ionization of Sb and Bi Ions

Abstract

At energies greater than 200 eV the electron-impact single-ionization cross sections for ${\mathrm{Sb}}^{2+}$($4{d}^{10}5{s}^{2}5p$) and ${\mathrm{Bi}}^{2+}$($5{d}^{10}6{s}^{2}6p$) ions, ${\ensuremath{\sigma}}_{2,3}$, are larger than the corresponding cross sections, ${\ensuremath{\sigma}}_{1,2}$, for ${\mathrm{Sb}}^{1+}$ and ${\mathrm{Bi}}^{1+}$ ions, respectively. This extraordinary behavior is a consequence of the fact that the $4d(5d)$ hole configurations goes from autoionization to bound when the charge state of the Sb (Bi) ions is increased from +1 to +2. Additionally, multiple ionization measurements (${\ensuremath{\sigma}}_{1,3}$ for Sb and ${\ensuremath{\sigma}}_{1,3}$, ${\ensuremath{\sigma}}_{2,4}$, and ${\ensuremath{\sigma}}_{3,5}$ for Bi) are presented for electron energies up to about 1000 eV.