Experimental and theoretical study of electron-impact ionization of atomic ions in the Sm isonuclear sequence

Abstract

Experimental measurements and theoretical calculations of absolute cross sections are carried out for the electron-impact ionization of atomic ions in the Sm rare-earth-metal isonuclear sequence. Absolute cross sections for ${\mathrm{Sm}}^{q+}$ ions for $q=1\ensuremath{-}12$ were measured using the electron-ion crossed-beam technique and calculated with the configuration-average distorted-wave method for the charge states $q=4\ensuremath{-}12.$ The theory includes both direct ionization and excitation-autoionization contributions, and includes transitions from both ground and metastable levels. We present the cross sections in an electron-impact energy range from threshold up to 1000 eV for all Sm ions up to ${\mathrm{Sm}}^{12+}.$ These systems are extremally complex, but the configuration-average method, when combined with statistical averaging of the cross sections over the many levels, provides results that are in overall good agreement with the experimental measurements. The single-ionization cross sections are dominated by contributions from indirect mechanisms of excitation-autoionization in the low-energy region.