Electron impact ionization of the hydrogen-like ions B⁴⁺, C⁵⁺, N⁶⁺and O⁷⁺

Abstract

For the first time absolute cross sections for electron impact ionization of the hydrogen-like ions B 4+ , C 5+ , N 6+ and O 7+ at electron energies from below threshold up to about 6 keV have been measured using the crossed-beams technique. All measured cross sections are in very good agreement with available distorted-wave exchange calculations and the semiempirical Lotz formula. The behaviour of the classically scaled cross sections along the hydrogen isoelectronic sequence is discussed. A recently developed scaling technique allows us to predict all non-relativistic cross sections along the isoelectronic sequence on an absolute scale.

Physical Mechanisms and Scaling Laws ofK-Shell Double Photoionization

“…For the He-like targets, Z Ã ¼ Z. Since along the hydrogen isoelectronic sequence a universal scaling e I 2 ¼ fðE e =IÞ works quite well [28], the relative strength of the KO contribution should scale with the square of the ionization potentials for a He-like ion and for the same neutral atom, respectively.…”

Electron impact ionization of hydrogen-like molybdenum ions

“…In the range of Z around 42 the relativistic effects and the effect of Breit interaction start to become more important [12]. In the case of H-like Fe at Z = 26, the cross sections can be expressed with the semi-empirical formulae proposed by Lotz [5] and by Aichele et al [3]. We will compare our results with those obtained with these scaling formulae and test their validity.…”

“…Therefore, it is expected that the formula proposed by Aichele et al [3] could not reproduce the experimental results in such region, since their formula did not consider these effects. However, we can conclude that their formula can be used, at least for the elements with Z 42 up to the energy E M given by their formula.…”

“…Recently, a universal shape function has been proposed [3,25], which has a 1/E e dependence in the high energy limit and an E e − I dependence near the ionization threshold: ) where I H is the ionization energy of the hydrogen atom and a 0 the Bohr radius.…”

Photoinduced K-shell hollow atoms

“…Because the shake-off asymptotic non-relativistic highenergy limit can be calculated quite accurately for the helium isoelectronic sequence and it is almost the same for neutral atoms and He-like ions [42,47], for R ∞ the values from Forrey et al [48] were used. For the knock-out probability P KO (E), the analytical form of the universal shape function for electron impact ionization of Hlike ions of Aichele et al [49] was adopted. The choice of the shape function was based on the similarity of electron-impact ionization of a H-like ion to the KO part of the double photoionization of the corresponding He-like ion [44,10,9,45].…”