ELECTRON EMISSION FROM DRESSED PROJECTILES IN COLLISION WITH ATOMS AND MOLECULES AT INTERMEDIATE ENERGIES

D. FREGENAL; J.M. MONTI; J. FIOL; G. BERNARDI; S.G. SUÁREZ; R. SCHUCH; L.M. RODRÍGUEZ; P.D. FAINSTEIN; R.D. RIVAROLA

San Carlos de Bariloche

Conferencia; 17th International Conference on the Physics of Highly Charged Ions; 2014

Electron distributions from collisions between dressed projectiles and atoms or molecules are determined by the emission from both collision partners. In the forward direction in particular, at electron velocities matching the projectile incident velocity, exists a noticeable peak structure (electron loss peak, ELP) which is superimposed to the target electron emission [1]. This structure may be produced either in direct ionization or as a result of simultaneous projectile and target ionization. Modelling ELP requires the calculation of the contributions of each of these processes, considering all possible electronic states involved.In this work we present theoretical and experimental results for angular and energy distributions of electrons emitted in the ELP energy region in collisions of dressed projectiles with atoms and molecules. In order to study the dependence of the ELP on the electronic initial state, different initial charge states (q = -1, 0, 1, 2) were selected according to the projectile species (B, C, Li, Na and F). The influence of the target on the ELP dynamics was analyzed by using H2, He, Ne and Ar gases. Projectile incident energies varied between 50 keV/u and 450 keV/u.For charged projectiles the ELP shows a single cusp at the corresponding projectile velocity as expected. However data taken for incident neutral atoms show also a second structure at lower energies, with a position that depends on the target species.The experimental data are compared with theoretical calculations based on a 4-body Classical Trajectory Monte Carlo (CTMC) approximation and three-body Continuum Distorted Wave (CDW) and Continuum-Distorted-Wave-Eikonal-Initial-State models (CDW-EIS). These results include the contributions to the ELP from target ionization, projectile ionization and simultaneous ionization channels. Quantum calculations also discriminate the emission from the different projectile shells. The models describe qualitatively well the data for ion impact but fail to reproduce the observed double structure. We discuss the possible origin of the double structure in terms of target ionization induced by electron-electron interaction.