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 Sb 2 + (4d l0 5s 2 5p) and Bi 2+ (5d l0 6s 2 6p) ions, o-2 ,3, are larger than the corresponding cross sections, 0x2, for Sb 1 + and 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 (0-1,3 for Sb and ox3, 0-2,4, and 0-3,5 for Bi) are presented for electron energies up to about 1000 eV.PACS numbers: 34.80.DpRecently, some basic understanding has been gained on multiple ionization of atomic ions via single collisions with electrons. 1 " 4 The large cross sections observed, especially for complex ions, may be attributed to single-ionization events ejecting an electron from one of the inner shells followed by the emission of one or more additional electrons via autoionization processes. However, no adequate attention has yet been given to the mutual interdependence of multiple and single electron-impact ionization of ions: Collision strength from a given subshell missing in the cross section v qfq + \ for single ionization of a #-fold charged ion can be found in the cross section o-qg + 2 for double ionization and vice versa depending on the possibility of an inner-shell ionization-autoionization mechaism.In this Letter we discuss the shift of d electron collision strength between single and double ionization of Sb« + (tf-1,2) and Bi« + (# =1,2,3) ions which are homologous with configurations 4d l0 5s 2 5p 3~q and 5d l0 6s 2 6p 3~Q , respectively. The starting point of this investigation was the observation of an unusual behavior of cross sections ox,2 an d °*2,3 f°r Sb 1 + (Bi 1+ ) and Sb 2+ (Bi 2+ ) ions, respectively. At electron energies above about 200 eV we found o-2 ,3 > (7i )2 ; i.e., for these species it is easier to remove an electron from the doubly charged ion (ionization potentials 5 of 25.3 eV for Sb 2 + and 26.6 eV for Bi 2 + ) than to remove an electron from the singly charged ion (ionization potentials 5 of 16.24 eV for Sb 1+ and 16.69 eV for Bi 1 + ). A second important experimental result is the observation of the largest cross sections for double ionization ever found for an atomic ion with ox3~6.5xl0" 17 cm 2 for Sb 1+ and ox, 3~7 .5 xl0" 17 'cm 2 for Bi 1+ , while the ions Bi 2+ and Bi 3 + have considerably smaller double-ionization cross sections (0-2,4-2.7 xlO" 17 cm 2 and 0-3,5-1.9 xlO" 17 cm 2 at maximum) and are almost equal above 500 eV. We will demonstrate below that this extraordinary behavior is due to the fact that the 4d (5d) hole configuration goes from autoionizing to bound as one goes fromSb 1+ (Bi 1+ ) toSb 2+ (Bi 2 + ) ions.For the measurement of ionization cross sections we have employed a new experimental technique 6 with crossed electron and ion beams which is based on the "animated-beams method 7 " of Brouillard and coworkers. However, instead of sweeping the electron b...

Ionization and fragmentation of fullerene ions by electron impact

“…12.25 eV [11]). We have previously observed [13] a similar extraordinary behavior for the corresponding cross sections 01,2 and 02,3 for Sb and Bi ions, where the Ad (5d) hole configuration goes from autoionizing to bound when the charge state is increased as one goes from Sb* (Bi + ) to Sb 2+ (Bi 2+ ). The effect in the fullerene ions may be similarly caused by autoionizing versus bound hole configurations.…”

The 5d photoabsorption spectra of Pb III and Bi IV

“…Loch et al [13] studied electron impact ionization of Bi q+ , q = 1-10 and compared configurationaverage distorted wave calculations to experimental results finding good agreement between both for all ion stages. Müller et al [14] employed crossed electron and ion beams to study single and double ionization of Bi I where they observed a crossing of the cross-sections for singly and doubly-charged Bi ions at electron energies over 200 eV.…”