S. Otranto

Evidence of electron saddle swap oscillations in angular differential ion-atom charge exchange cross sections

State selective charge exchange processes in 1-10 keV/amu Ne8+ +Na(3s) collisions were measured by means of the magneto-optical trap recoil-ion momentum spectroscopy technique and compared to classical trajectory Monte Carlo calculations. We find that for electron capture to n-levels >= 10, the transverse momentum distributions exhibit an oscillatory structure which is very sensitive to the impact energy. Our theoretical analysis suggests that this feature is a direct consequence of the number of swaps the electron undergoes across the potential energy saddle during the charge exchange process.

State-selective charge exchange from Na(3s) and Na*(3p) by highly charged ions

State-selective charge exchange cross sections and momentum spectra are calculated for collisions of Xe18+ and Xe54+ ions with Na(3s) and Na*(3p) over the energy range of 0.1–10.0 keV/amu. The classical trajectory Monte Carlo method is used which includes all two-body interactions. The n-level cross sections are found to be rather insensitive to collision energy below 1 keV/amu. In contrast, the transverse momentum cross sections for specific n-levels change rapidly with energy. However, this latter variation in energy is found to be in general agreement with simple scaling rules. Experimental state-selective data are available for Xe18+ over a limited energy range; they are found to be in reasonable accord with the calculations.

Focusing effects by one and two Coulomb centers in the autoionization of He

In this work we consider the autoionization of He following double electron capture in He2+ + H2 collisions at an impact energy of 14 keV/amu. The post-collisional interaction with the two Coulomb centers is treated within the Barrachina-Macek model by employing the Φ2 correlated wave function introduced by Gasaneo et al to represent the continuum of the emitted electron in the field of two Coulomb centers. We compare the angular profiles in the electron spectrum with those obtained following double electron capture for the collision system He2++ He. Clear differences are observed in the spectra obtained for the atomic and molecular targets.

Water fragmentation by Liq+and Cq+projectiles with MeV energies

We report on fragment distributions from water targets by impact of Liq+ and Cq+ projectiles with MeV energies. We identify fragment species as function of emission energy by using an electrostatic spectrometer and as function of velocity by a time of flight mass spectrometer (pulsing the beam at the injector of the Pelletron accelerator). An improved Coulomb explosion model married to CTMC simulations allows us to calculate the energy of each fragment for different fragmentation channels.

Double ionization of helium by ion impact: second Born order treatment at the fully differential level

In this work, a theoretical study of the double ionization of He by ion impact at the fully differential level is presented. Emphasis is made in the role played by the projectile in the double emission process depending on its charge and the amount of momentum transferred to the target. A Born-CDW model including a second-order term in the projectile charge is introduced and evaluated within an on-shell treatment. We find that emission geometries for which the second-order term dominates lead to asymmetric structures around the momentum transfer direction, a typical characteristic of higher order transitions.

The role of multiple electron capture in the x-ray emission process following charge exchange collisions with neutral targets

In this work we theoretically study photonic spectra that follow charge exchange processes between highly charged ions and neutral argon and CO targets. The range of collision energies studied is 5 eV/amu-10 keV/amu, covering typical EBIT-traps and Solar Wind energies. Our studies are based on multiple electrons schemes within the classical trajectory Monte Carlo method. Electrons are sorted with the sequential binding energies for the target under consideration. The role played by the multiple electron capture process for the different collision systems under consideration is explicitly analyzed and its contribution separated as arising from double radiative decay and autoionizing multiple capture. Present studies are stimulated by the upcoming launch of the Astro-H mission in 2015, which will provide high resolution spectra in the 0.3 keV-12keV band.

Recoil-ion momentum spectroscopy for He2+ + He electron capture reactions

Electron capture reactions for 3He2+ collisions on He at impact energies in the range 40 keV-300 keV have been studied using the Cold Target Recoil-Ion Momentum Spectroscopy setup which has recently became operational at the Centro Atomico Bariloche. State-selective charge exchange cross sections were obtained and in this work we present recoil-ion transverse momentum distributions. For targets with residual thermal motion, we show that the implementation of a back-projection algorithm based on the transverse momentum distribution component along a direction perpendicular to the jet direction provides results in agreement with those obtained by using previously cooled targets. Present results nicely fit the gaps in the datasets already published by other laboratories and are found to be in good agreement with classical trajectory Monte Carlo simulations.

Double ionization of Helium by bare ions: theoretical study of the fully differential cross sections

In this work we study the double ionization of He induced by fully stripped projectiles. Distorted wave models based on effective charges which dynamically couple the two-body subsystems are compared to simpler models widely studied in the literature. The influence of the projectileś velocity and charge sign and magnitude on the fully differential cross sections (FDCS) are analyzed.

Double ionization of helium by bare ions: Theoretical study of the fully differential cross sections

This work presents a theoretical study of fully differential cross sections (FDCSs) for the double ionization of an He target by ion impact within a distorted wave model. The initial atomic system is described by two approximated wave functions of different accuracy proposed by Bonham and Kohl. For the final channel several models are considered based upon improvements and simplifications of the well-known three-body Coulomb (3C) model. The influence of the receding projectile on the resulting fragments is also studied by implementing a model with effective charges that depend on the momenta of the four particles. The FDCSs resulting for different electron energy sharing are discussed. The sensitivity of the FDCSs to the projectile charge sign and magnitude is explored over the energy range 700 keV/amu through 6 MeV/amu.

State-selective electron capture in {sup 3}He{sup 2+} + He collisions at intermediate impact energies

In this work we have measured single-electron capture in collisions of {sup 3}He{sup 2+} projectiles incident on a helium target for energies of 13.3-100 keV/amu with the cold-target recoil-ion momentum spectroscopy setup implemented at the Centro Atomico Bariloche. State-selective single-capture cross sections were measured as a function of the impact energy. They were found to agree with previous existing data from the Frankfurt group, starting at the impact energy of 60 keV/amu; as well as with recent data, at 7.5 keV/amu, from the Lanzhou group. The present experimental results are also contrasted to the classical trajectory Monte Carlo method with dynamical screening.