C. R. Garibotti

Hypergeometric integrals arising in atomic collisions physics

We introduce a method of obtaining volume integrals involving confluent hypergeometric functions. This method is based on the integral representation of these functions and enabled us to write a generalized Nordsieck integral in terms of hypergeometric functions of many variables. We explore some particular results that could be useful when calculating transition matrices in collision theories.

Electron-ion correlation effects in ion-atom single ionization

We study the effect of electron-ion correlation in single ionization processes of atoms by ion impact. We present a distorted wave model where the final state is represented by a correlated function solution of a non-separable three-body continuum Hamiltonian, that includes electron-ion correlation as coupling terms of the wave equation. A comparison of the electronic differential cross sections computed with this model with other theories and experimental data reveals that the influence of the electron-ion correlation is more significant for low energy emitted electrons.

Multivariable hypergeometric solutions for three charged particles

We present a new wavefunction which describes the ion - atom problem above the ionization threshold. This is an approximate solution of the Schrodinger equation for the three-body Coulomb problem that can be expressed in terms of a confluent hypergeometric function of two variables. The proposed wavefunction includes correlation among the motions of the three particles and verifies the correct Coulombic asymptotic behaviours.

Double ionization of atoms by ion impact: two-step models

Total cross sections for the double ionization of He and Li atoms by the impact of H+, He2+ and Li3+ are calculated at intermediate and high energies within two-step models. The double ionization of He by the impact of other bare projectiles at a fixed energy is obtained as well. Single ionization probabilities are calculated within the continuum distorted wave –eikonal-initial-state (CDW–EIS) approximation. The required atomic bound and continuum wave functions are evaluated by numerically solving the atomic wave equation with an optimized potential model (OPM). Correlation between events is introduced by considering ion relaxation. The final state electronic correlation is considered by means of the so-called Gamow factor. We compare the transition probabilities resulting from our approach with those resulting from the use of a Rootham–Hartree–Fock initial state and a Coulomb continuum state with an effective charge. We find that the use of OPM waves gives a better agreement with the experimental results than with Coulomb waves.

Multivariable hypergeometric functions for ion–atom collisions

Abstract In this work we present a correlated wave function for a three-body continuum Coulomb problem. This state is described by the two-variables Φ 2 hypergeometric function. We examine the properties of this function and their differences with previous uncorrelated models. The Φ 2 wave function can be considered as a final state of ion–atom ionizing collisions, giving rise to both undistorted (Born- Φ 2 ) and distorted (EIS- Φ 2 ) models. We obtain double differential cross sections with the Born- Φ 2 theory for proton–helium collisions in the intermediate to high energy regime. They exhibit all the main features of the electronic emission process and agree with the experimental data.

Intra- and intercycle interference of electron emissions in laser-assisted XUV atomic ionization

Fil: Gramajo, Ana Alicia. Comision Nacional de Energia Atomica. Gerencia del Area de Energia Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina

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.

Continuum states in ion-atom collisions

Abstract We review the experimental and theoretical situation for ionization collisions of nude ions with neutral gas atoms, at intermediate and high impact energies. We consider particularly that part of the electron spectrum where emission is larger, corresponding to the joint action to the two ions. We discuss the evidence of this two-center interaction and how it is described by current theories.

Non-constant ponderomotive energy in above threshold ionization by intense few-cycle laser pulses

We analyze the above threshold ionization of hydrogen atom by strong and short laser pulse with a simple envelope temporal dependence. We find additional peaks in the resulting ATI spectra originated from different values of the ponderomotive energy and the interference due to the electronic emission at different times.

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.