The influence of angular momentum on double electron capture by highly charged ions

Abstract

Double electron capture during collisions of highly charged ions with H2 or He is studied by measuring and analyzing energy spectra of the resulting autoionization electrons and by comparing the experimentally determined population probabilities for the various states with those calculated from a simple classical model. This model is based on the extended classical over-barrier model (ECBM), modified by taking additionally the angular momenta of the exchanged electrons into account. Reasonable agreement between measured and calculated population probabilities for the highly correlated two-electron states is obtained especially for the cases of fully stripped projectiles, although correlation during the exchange process is neglected in the theoretical description. The success of the model implies that highly oriented doubly excited states result from the capture process.

Hollow ion formation studied by electron spectroscopy of18O8+-C60at 4.4 keV/amu*

“…The challenge for experimentalists is to then identify the processes which can explain the ejection of such a large number of electrons, and the investigation of these processes by electron spectroscopy seems necessary to gain a better understanding. At low collision velocity v coll , typically for v coll < 1 au, multiple capture predominates and the electron spectrum should have strong similarities with those already measured with heavy atomic targets [2][3][4][5]. However, the interaction of a multicharged ion with a C 60 cluster is particular in several respects.…”

“…The C 60 cluster is a reservoir of a lot of weakly-bound electrons, the successive ionization potentials are small and rather similar. The first to seventh ionization potentials of C 60 lie within the 7.4 to 27 eV range [6], to be compared with the corresponding ionization potentials of the argon atom, already used as a target in previous studies [2][3][4][5], which range from 15.8 to 124.3 eV [7]. Therefore the C 60 cluster is often considered as an intermediate object between an atom and a metal surface and, apart from its intrinsic interest, it may be used to gain a better understanding of the hollow ion formation and decay in front of a surface (see for example [8,9]).…”

Double electron capture inNe8+-He collisions at intermediate energies

“…Extensions of the model to include the angular momentum distributions have had little success in the description of what is observed spectroscopically. Recently Posthumus, Lukey, and Morgenstern [8] using the extended over-barrier model have had some success in describing the angular momentum distribution for double electron capture for bare projectiles, but less suc-cess for double electron capture in He-like projectiles. All their measurements were made at very low projectile velocities U «1 a.u.…”

State-selective Charge Exchange in 19.5–100 keV amu−1 O6+ Collision with He and H2

“…Seely et al (2017) found that autoionizing double capture can lead to an enhancement of X-ray emission following single capture. In addition, basic CX mechanisms for doubly excited state formation have been extensively studied in the keV energy range (Stolterfoht et al 1986;Winter et al 1987;Roncin et al 1989;Posthumus et al 1992;Raphaelian et al 1993;Chesnel et al 1996;Fléchard et al 2001;Zhang et al 2001Zhang et al , 2016Roncin 2020;Guo et al 2023). However, the collision energy dependence of doubly excited states has been sparsely reported for state-resolved double CX.…”