Double ionization of neutral atoms, positive and negative ions by electron impact

Abstract

New experimental data on double-ionization cross sections of neutral atoms, positive and negative ions by electron impact are reported. These and other relevant data are compared with recent multiple-ionization semiempirical formulae extended for the case of two-electron ionization. Theory gives analytical dependence of the double-ionization cross sections on the main parameters of the collision system in a wide energy range. For the He atom, He-like ions and H − ion high-energy asymptotic behaviour of the double-ionization cross sections are considered on the basis of a quantum mechanical treatment. Suggested cross section scaling for fast collisions, employing a target-effective nuclear charge, is in good agreement with experimental data.

Influence of Electron-Impact Multiple Ionization on Equilibrium and Dynamic Charge State Distributions: A Case Study Using Iron

“…Shevelko & Tawara (1995a, 1995b) presented a semiempirical formula that describes cross sections for direct multiple ionization of at least three electrons, i.e., triple ionization, from neutral and ionic targets. Bélenger et al (1997) extended their formulae to double ionization. The direct multiple ionization cross sections are approximated by…”

Double Ionization of H−Ions by Electron Impact in the Solar Atmosphere

“…The double-ionization cross sections ( 0 H À 2 ) for v 3 v 0 , including the additional corrections (Bélenger et al 1997) for the high-energy tail due to distant and close collisions, correspond to experimental high-energy ionization of H À :…”

“…However, our theoretical understanding of multi-electron ionization of target systems by electron impact has been hindered by a lack of quantum mechanical calculations, because of many-body correlations in the final channel. Therefore, semiempirical models for multi-electron ionization cross sections have been extensively explored ( Bélenger et al 1997) and compared with experimental results (Shevelko & Tawara 1998). It has been found that the semiempirical Bethe-Born formula (Shevelko & Tawara 1998) reproduces the observed data quite well for most cases.…”

“…where the parameters for H À are given by a(2) ¼ 14:0, b(2) ¼ 1:08, and I 2 ¼ 14:35 eV (Bélenger et al 1997). …”

“…In particular, the phenomenon of multiple ionization of atoms and ions by electron impact (Bélenger et al 1997;Shevelko 1997;Shevelko & Tawara 1998) has played an important role in modeling astrophysical and laboratory plasmas. It is known that the H À ion plays an important role in the transport of energy through the solar atmosphere ( Bethe & Salpeter 1957;Chandrasekhar 1958;Harwit 1988), since hydrogen can become the negative hydride ion H À by gaining an electron.…”