Two-electron cusp in the double ionization of helium

Abstract

We analyze the double ionization of He under the impact of 100 keV He 2+ projectiles. The process is described within the framework of the impact parameter and frozen-correlation approximations where the one-electron events are treated by the continuum distorted wave method. Correlation between the emitted electrons, which plays an important role in forming the shape of the differential distribution of the electron emission, is described by the Coulomb density of states approximation (CDS). Special attention is paid to the region of the two-electron cusp that has been observed in a recent experiment for 100 keV He 0 + He collisions [L. Sarkadi and A. Orbán, Phys. Rev. Lett. 100, 133201 (2008)]. In the cusp region the correlated motion of the two electrons is influenced dominantly by the outgoing projectile, that is, the correlation function of the CDS treatment is expected to depend on the electron momenta measured relative to the projectile rather than to the target nucleus. A qualitative agreement with the experiment is achieved with a CDS model based on the use of such a projectile-centered correlation function that applies effective charges as given in the dynamically screened three-Coulomb wave function.

Triple-coincidence experiment to study the correlated electron emission in the collision-induced double electron loss of He−

“…In subsequent theoretical works on the two-electron cusp [19,28] attempts were made to reproduce the observed energy correlation. In these works a simpler collision system was considered, namely, the double ionization (DI) of He by He 2+ , instead of the complicated mutual ionization of the target and projectile in He 0 + He collision.…”

“…Both approaches treated the electron emission in the independent particle model using the continuum distorted wave method, but applied different correction methods for the inclusion of the electron correlation. Gulyás et al [28] proposed a correction procedure based on the Coulomb density of states approximation. In their model the electron-electron interaction was taken into account in the final continuum state of the electrons by introducing a dynamically screened effective charge in the Coulomb normalization factor of the wave function.…”

Electron transfer plus double ionization in slow He2+ + Ar collisions

“…Theoretically, double ionization by ion impact has been studied extensively [24][25][26][27][28]. However, the lack of measured FDCS for multiple ionization processes represents a major limitation in sensitively testing theoretical descriptions of the few-body dynamics.…”

Double ionization of He by ion impact: Second-order contributions to the fully differential cross section

“…Most of them are based on two-and three-body correlated wave functions and all of them rest on some sort of approximation throughout their numerical implementation [25][26][27][28]. The postcollisional interactions between the receding projectile and the emitted electrons have been incorporated via the introduction of effective charges [25,29]. Models based in four-body wave functions have been applied to the (e,3e) process [30,31], but for DI by ion impact, the four-body dynamical coupling has only been accounted for using effective relative momenta [32].…”