P D Fainstein

Two-centre effects in ionization by ion impact

When an atom is ionized by ion impact, the electron is ejected into a final continuum state of a two-centre potential due to the Coulomb fields of the projectile and ionized atom. The related effects on the electron yield or energy and angular distributions are referred to as two-centre electron emission (TCEE). The present report is devoted to a discussion of experimental and theoretical evidence of this TCEE. The use of heavy ions or antiprotons as projectiles allows to unravel these effects by monitoring the two centre potential. On the theoretical side, the continuum distorted wave-eikonal initial state theory (CDW-EIS) accounts for the TCEE thus allowing a detailed interpretation of the experimental findings.

A theoretical model for ionisation in ion-atom collisions. Application for the impact of multicharged projectiles on helium

The continuum-distorted-wave-eikonal-initial-state model is extended to describe single-electron ionisation by impact of bare projectiles on multielectronic targets. Applications are given for collisions between multicharged ions and helium. Double differential, single differential and total cross sections are calculated. Experimental data and present theoretical results show deviations from the square of the projectile charge dependence predicted by the first Born approximation.

CDW-EIS theory of ionization by ion impact with Hartree-Fock description of the target

We have carried out a generalization of the continuum-distorted-wave-eikonal-initial-state (CDW-EIS) approximation for ion-impact single ionization where the interaction of the active electron with the target is represented by a Hartree-Fock potential. We apply this model to the ionization of He, Ne and Ar by proton and multiply-charged bare-ion impact. Doubly differential and total cross sections are calculated from each subshell. These cross sections summed over all subshells show a much better agreement with experimental data than those obtained from the previous formulations of the CDW-EIS approximation which use hydrogenic wavefunctions with effective charges.

Theoretical Calculation of Electronic Stopping Power of Water Vapor by Proton Impact

The energy loss of proton beams in water vapor is analyzed with a full quantum-mechanical treatment, the distorted-wave model. This model takes into account distortion effects due to the long-range Coulomb potential. Projectile energies from 10 keV up to 1 MeV are considered. Mean stopping power and equilibrium charge-state fractions are calculated and compared with experimental data. The validity of Braggs additivity rule is investigated.

Distorted wave theories for dressed-ion–atom collisions with GSZ projectile potentials

The continuum distorted wave and the continuum distorted wave-eikonal initial state approximations for electron emission in ion–atom collisions are generalized to the case of dressed projectiles. The interaction between the dressed projectile and the active electron is represented by the analytic Green–Sellin–Zachor (GSZ) potential. Doubly differential cross sections as a function of the emitted electron energy and angle are computed. The region of the binary encounter peak is analysed in detail. Interference structures appear in agreement with the experimental data and are interpreted as arising from the coherent interference between short- and long-range scattering amplitudes.

Theoretical calculations of the stopping power for protons traversing H, He and simple molecular targets

Abstract Stopping power calculations for protons traversing H, He and H2O gas targets in the energy range (10 keV–1 MeV) are presented. Theoretical models which include charge-state and high order effects are used. By using molecular wave functions, deviations from Braggs rule are studied.

K-Shell vacancy production in asymmetric collisions

Abstract The Continuum Distorted Wave-Eikonal Initial State approximation is introduced to describe electron capture in ion-atom collisions. The model had been previously studied to represent electron ionization. Theoretical total cross sections for both processes are compared with experimental data for impact of light bare ions on heavier targets.

CDW-EIS model for single-electron capture in ion-atom collisions involving multielectronic targets

A generalization of the continuum distorted wave eikonal initial state (CDW-EIS) approximation, for the description of single-electron capture in ion–atom collisions involving multielectronic targets is presented. This approximation is developed within the framework of the independent electron model taking particular care of the representation of the bound and continuum target states. Total cross sections for single-electron capture from the K-shell of He, Ne and Ar noble gases by impact of bare ions are calculated. Present results are compared to previous CDW-EIS ones and to experimental data.

Single electron capture differential cross section in H+ + He collisions at intermediate and high collision energies

The generalized continuum distorted wave-eikonal initial state (CDW-EIS II) approximation is employed to study differential cross sections (DCS) for single electron capture in H+ + He collisions at intermediate and high energies. Present results are compared with theoretical calculations obtained using the previous CDW-EIS formulation in order to show the importance of the description of the bound and continuum target states in the entrance and exit channels, respectively. Both DCS are also shown together with other theoretical results and with experimental data.

The continuum distorted wave eikonal initial state model for transfer ionization in H+, He2+ + He collisions

We employ the independent-event model to study the transfer-ionization (TI) process in H+, He2+ + He collisions. We consider both the ionization-capture and capture-ionization paths. The single-particle probabilities for all channels are calculated with the continuum distorted wave eikonal initial state model. With the probabilities for TI we calculate doubly differential and total cross sections which are compared with the available experimental data. Our present results are in better agreement with the experiments than present calculations using the independent-electron model and previous calculations using the independent-event model, but with single-particle probabilities calculated with the continuum distorted-wave model.