J. Fiol

Critical comparison between theory and experiment for C6++He fully differential ionization cross sections

Fully differential cross sections for single ionization of helium induced by impact of 100 MeV/u C6+ ions are examined within a quantum-mechanical distorted wave model. The experimental uncertainties are included in the theoretical calculations, leading to a quantitative description of the experimental cross sections. In particular, the ionization cross section for the electron emitted in the plane perpendicular to the scattering plane is reproduced for the first time by a full quantum-mechanical model. The role of the internuclear interaction in this perturbative-regime collision is discussed and found to be unimportant for the present kinematical conditions.

Vortices in ionization collisions by positron impact

The presence of vortices in the ionization of hydrogen atoms by positrons at intermediate impact energies is investigated. The present findings show that a previously reported minimum in the fully differential cross section is the signature of a vortex in the continuum positron–electron–proton system. The behaviour of the real and imaginary parts of the complex-valued transition matrix is studied in order to determine and characterize the vortex in momentum space. The obtained information is translated to fully differential ionization cross sections, feasible of being measured with currently available techniques.

Experimental and theoretical results on electron emission in collisions between He targets and dressed Liq+ (q = 1, 2) projectiles

We investigate experimentally and theoretically the electron emission in collisions between He atoms and (q = 1, 2) projectiles at intermediate to high incident energies. We report on measured absolute values of double-differential cross-sections, as a function of the emitted electron energy and angle, at a collision energy of 440 keV u−1. The different contributions from target ionization, projectile ionization, and simultaneous target–projectile ionization are calculated with the quantum-mechanical continuum distorted wave and continuum distorted wave–eikonal initial state models, and with classical trajectory Monte Carlo simulations. There is an overall good agreement of the calculations with the experimental data for electron emission cross-sections.

Experimental and theoretical results on electron emission from helium by the impact of bare Li3+ ions

We investigate experimentally and theoretically the ionization of helium atoms by the impact of bare Li3 + projectiles at intermediate and high incident energies. We report on measured absolute values of doubly differential cross-sections, as a function of the emitted electron energies and angles, at collision energies of 200 and 440 keV u−1. Different physical aspects of the reaction are interpreted theoretically by comparison of the data with quantum-mechanical continuum distorted wave and continuum distorted wave–eikonal initial state calculations as well as classical trajectory Monte Carlo simulations. There is an overall good agreement of the calculations with the experimental data, which improves considerably for higher collision energies.

Laser pulse ionization of fixed-in-space H2O

We present a detailed study of the ionization probability of H2O induced by a short intense laser pulse. Within the strong-field approximation, we present total and differential ionization probabilities of the water molecule fixed in space. It is shown that the second highest occupied molecular orbital (HOMO-1) dominates the single-electron emission process when the laser is polarized along the symmetry axis of the H2O molecule, and that the electron emission is in general favoured in the direction along the laser polarization direction.

Angular distributions and Dalitz plots for C6+ ionization of He

Single ionization fully differential cross sections for 2 MeV/amu C6+ + He collisions are obtained and analysed using the classical trajectory Monte Carlo and continuum distorted wave models. The present theoretical results are compared with the recent experimental data of Fischer et al. The published experimental conditions are considered in both theoretical models. The inclusion of the momentum distribution of the target atom leads to an improved description of the forward electron emission. Dalitz plots for single ionization fully differential cross sections in ion–atom collisions are presented and are used to help elucidate the collision dynamics.

Factorization of laser-pulse ionization probabilities in the multiphotonic regime

We present a detailed study of the ionization probability of H and H induced by a short intense laser pulse. Starting from a Coulomb–Volkov description of the process we derive a multipole-like expansion where each term is factored into two contributions: one that accounts for the effect of the electromagnetic field on the free-electron final state and a second factor that depends only on the target structure. Such a separation may be valuable to solve complex atomic or molecular systems as well as to interpret the dynamics of the process in simpler terms. We show that the series expansion converges rapidly, and thus the inclusion of the first few terms is sufficient to produce accurate results.

Momentum-transfer dependence of ionization cross sections for C6++He collisions

In this work we study the dependence of the fully differential cross sections (FDCS) for single ionization of He by 100 MeV/amu C6+ on the momentum transferred by the projectile to the target. Three dimensional plots of the FDCS are used to illustrate how the different configurations contribute when the theoretical results are convoluted over the experimental uncertainties. This convolution is shown to be essential in order to properly reproduce the measured data.

Fully differential ionization cross sections in fast ion-atom collisions

Fully differential cross sections for helium ionization by fast ion collisions are analyzed. The emitted-electron angular distributions for fixed momentum transfer and electron energies are described theoretically and compared to the experiment. The effect of uncertainties in the determination of the momentum is considered within the theoretical model. The cross sections are found to be extremely sensitive to the inclusion of the uncertainties. Important quantitative and qualitative modifications of the calculated cross sections are obtained by including small uncertainties in the determination of the momentum transferred by the projectile to the target.

Electron emission in collisions of dressed ions with He atoms

We present theoretical and experimental results for angular and energy distributions of electrons emitted in collisions of B2+ with He atoms. In particular, we analyze the cusp formed by projectile Electron Loss to Continuum (ELC) and Electron Capture to Continuum (ECC). The cusp shape dependence on the electronic initial state is discussed and compared with our previous measurements on Li+ + He. The projectile incident energy was about 414 keV/u and the electron detection angle was varied between 0° and 150°. The experimental data is compared with three-body quantum Continuum-Distorted-Wave calculations.