Resonance effects in near-threshold electron-impact excitation of the 143.4 nm line in the Pb+ ion*

Abstract

Electron-impact excitation of the resonance transition 6s 26d 2 D 3/2 → 6s 26p 2 P o 1/2 (143.4 nm) in the Pb+ ion within the (6–100) eV energy range is studied spectroscopically using a crossed-beam technique. The observed distinct structure in the energy dependence of the effective excitation cross section (including the energy region above the ion ionization potential) is primarily due to the decay of atomic and ionic autoionizing states, produced mainly by excitation of an electron from the subvalence 5d 10 shell, to the resonance levels (directly or via the cascade transitions). The absolute cross section value for the line under investigation was determined by normalizing the experimental curve at the electron beam energy of 100 eV to the theoretical data obtained by the Van-Regemorter formula and found to be (0.5 ± 0.3) × 10-16 cm2.