G Bernardi

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.

Electron emission for transfer ionization in 70 keV H+ on He

We present experimental results for doubly differential electron emission in transfer ionization produced by H+ projectiles on a He target at 70 keV impact energy. Energy spectra were obtained at emission angles of = 0°, 20° and 50°, and compared with spectra of total electron emission, these being dominated by single ionization. A cusp-shaped emission of electrons at the velocity of the emerging H0 projectiles, and an enhanced electron emission from binary-encounter collisions are observed in the transfer ionization spectra.

Coincidence study of electron transfer to the continuum process in collisions at intermediate energies

Energy distributions of electrons ejected into the forward direction in 15-214 keV collisions were measured in coincidence with charge-state analysed outgoing projectiles. All spectra show a cusp-shaped peak centred at an electron velocity equal to that of the projectile. The peaks observed in coincidence with are associated with the electron-projectile Coulomb final-state interaction. On the other hand, the physical origin of the cusp-like structure observed in coincidence with neutral outgoing projectiles is still unknown. Here we present some new evidence that seems to indicate that this peak can be attributed to the dipole interaction between the emitted electron and an excited state of the outgoing projectile. The fractions of the cusp yields show that the electron transfer into the continuum process associated with emerging becomes more important for decreasing projectile energies.

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.

CDW and CDW-EIS calculations of simultaneous ionization in collisions between dressed projectiles and atomic targets

The role of simultaneous electron emission in collision between dressed ions and atoms is discussed. Methods of calculations within quantum-mechanical Continuum-Distorted- Wave (CDW) and Continuum-distorted Wave-Eikonal-Initial-State (CDW-EIS) models are revisited and improved within a semiclassical probabilistic approach.

Electron loss in collisions of dressed projectiles with atoms and molecules

Energy distributions of electrons emitted with energies corresponding to the region of the electron-loss-cusp (ELP) were measured for collisions of several neutral projectiles with atoms and small molecules. Besides the well known projectile ELP cusp, a second structure is observed for Li and Na projectiles. Comparing the experimental data with four-body CTMC calculations we analise the origin of these structures in terms of nuclear-electron and electron-electron interactions.

Electron emission in collisions between dressed Alq+ ions with He targets

Experimental and theoretical results are presented for electron emission in collisions between dressed Alq+ ions and atomic He targets. The experimental data are compared with a four-body CTMC model and two distorted wave models, namely the CDW and CDW-EIS. The contribution to total electron emission spectra from the ionisation of each collision center and as well as the simultaneous ionisation can be assessed separately.

Electron emission from dressed projectiles in collision with atoms and molecules at intermediate energies

Angular and energy distributions of electron emitted from dressed ions and neutral atoms in collisions with atoms and molecules were measured for intermediate incident energies. Effects of the initial state of the projectile electron were studied using distorted wave and CTMC calculations. Experiments carried out on collisions with He, Li, H, Ne, and Ar show that the electron loss distributions depend very strongly on the target.

Diffraction effects in electron loss from incident on Ar at 78 keV

We present an experimental study and a model calculation of the double differential electron-loss cross section produced by 78 keV colliding with Ar. At this low energy we find a structure in the measured angular and energy distributions that can be interpreted in terms of diffraction of the emitted electrons scattered by the field of the target. Comparison of the observed structure is made with known electron-Ar collision measurements. Our theoretical discussion is based on a quasifree electron scattering model including a partial wave expansion of the active electron. This model is capable of describing the essential features of the experimentally measured distributions.