S. E. Corchs

Electron capture from H2 targets by H+ and He2+ ions. Dependence of the cross sections on the orientation of the molecular axis

We study the electron capture process from molecular hydrogen targets by proton and alpha particle impact at high collision velocities. The dependence of the differential cross sections on the orientation of the internuclear axis of H2 is evaluated within a two effective center approximation for capture to selective final states of the projectile. In particular, the molecular B1B model is applied in the calculations. The molecular orientation effects observed are due to the interference between the scattering amplitudes from the two centers of the target.

Importance of the multicenter character of molecular aggregates in the theoretical description of the charge transfer process

Abstract In the present work we focus our interest on the electron capture process from H2+ by proton impact at high impact energies. The molecular-continuum distorted wave (M-CDW) and the corresponding two effective center (TEC-CDW) approximations are used to compute single differential (as a function of the molecular alignment) and total electron capture cross sections. In the M-CDW approximation the field created by both nuclei of the target is considered to act simultaneously on the electron in the exit channel. On the contrary, in the TEC-CDW approximation each one of these nuclei is considered to affect separately the captured electron. Then, the importance of the effects due to this multicenter character of molecular aggregates in the charge transfer process is studied through the comparison of theoretical cross sections obtained with both approximations for the H++H2+ system. It is found that multicenter effects are important for the study of differential cross sections as a function of the molecular orientation but they do not modify significantly the total cross sections. The origin of this behavior is interpreted in terms of the impact parameter dependence of the capture probability.

INTERFERENCE EFFECTS IN COLLISIONS BETWEEN HEAVY IONS AND MOLECULAR TARGETS

Abstract The transfer-excitation process in O8++H2 collisions is studied at high impact energies using an independent event model. The transfer-excitation probability is expressed as a product of a capture probability from H2 (PC), leaving the H2+ in its ground state, and an excitation probability (PE) of the residual target to a dissociative state. PC is evaluated in the Continuum Distorted Wave-Eikonal Final State (CDW-EFS) model and PE is calculated in the first Born approximation (FBA). The differential cross-sections are studied as a function of the molecular orientation and the interference patterns obtained are compared with the available experimental data.

Influence of the molecular alignment on electron capture from H2 by O8+ projectiles

Abstract The single electron capture process by impact of O8+ on H2 targets is studied. The Continuum Distorted Wave-Eikonal Final State (CDW-EFS) model, is used within a two independent center approximation. The influence of the molecular orientation on the single electron capture process is analyzed. Differential and total cross sections are calculated and compared with previous Oppenheimer-Brinkman-Kramers (OBK) results and experimental data.

Single electron capture by impact of multicharged ions

Single electron capture for intermediate and high collision energies is analyzed. Theoretical total cross sections for B5+, C6+, N7+, O8+ and F9+ projectiles impinging on H, He and H2 targets are presented. The Continuum Distorted Wave-Eikonal Final State approximation is employed in the calculations. The theoretical results are compared with available experimental data.

Total cross-sections for single electron capture from H, He and H2 targets by impact of Be4+ and B5+ ions

Single electron capture from H, He and H2 targets by impact of Be4+ and B5+ projectiles is studied for intermediate and high collision energies. Total cross-sections are calculated using the Continuum Distorted Wave-Eikonal Final State model. Theoretical results corresponding to capture to selective final bound states and to all final states are presented for impact energies ranging from 50 keV/amu to 3 MeV/amu. A comparison with available experimental data is also shown.

Independent center, independent electron approximation for dynamics of molecules and clusters

A formalism is developed for evaluating probabilities and cross sections for multiple‐electron transitions in scattering of molecules and clusters by charged collision partners. First, the molecule is divided into subclusters each made up of identical centers (atoms). Within each subcluster coherent scattering from identical centers may lead to observable phase terms and a geometrical structure factor. Then, using a mean field approximation to describe the interactions between centers we obtain AI∼∑k∏keiδkIAIk. Second, the independent electron approximation for each center may be obtained by neglecting the correlation between electrons in each center. The probability amplitude for each center is then a product of single electron transition probability amplitudes, aIki, i.e. AIk≊∏iaiki. Finally, the independent subcluster approximation is introduced by neglecting the interactions between different subclusters in the molecule or cluster. The total probability amplitude then reduces to a simple product of am...

Uniqueness of the minimal form of Coulomb asymptotic behaviour in atomic collisions

The authors study the formulation of atomic scattering in the impact parameter approximation. They first note that the asymptotic conditions for the case of Coulomb interactions are not defined unequivocally within the impact parameter approximation. They then show that any ambiguity can be waived when the impact parameter approximation is derived as the eikonal limit of the quantum equations. Finally, in showing the uniqueness of a minimal form of asymptotic conditions, they provide a proof of the celebrated prescription presented by Cheshire (1964).

Electron capture to selective excited states in ion–H2 collisions

Abstract Single electron capture by impact of protons and alpha particles on H2 targets is studied. The intermediate and high collision energies regimes are considered. The work is focussed on non-dissociative charge exchange reactions where the H2+ residual target stays in a molecular bound state after the collision. Cross sections are calculated using different distorted wave models related to the continuum distorted wave approximation. These cross sections are compared with Classical Trajectory Monte Carlo results and experimental data. Total cross sections for capture into selective final states (for proton impact) and also into any final bound state of the projectile are presented.