Single electron capture involving multielectron atomic targets

P. N. ABUFAGER, A. E. MARTÍNEZ, P. D. FAINSTEIN AND R. D. RIVAROLA

Donostia-San Sebastian España

Workshop; Workshop in honor of Antoine Salin: Recent advances on the dynamic of atomic and molecular particles interacting with gas and solid targets; 2005

 The dynamics of many-particle collisions is a very complex problem which involves the description of bound and continuum states of atoms and the possibility of many open channels. Although one active electron processes are most often the most important, nowadays it is possible to observe experimentally processes like multiple capture and ionization, transfer-ionization, capture-excitation and so on. The theoretical description of these reactions is very complicated. However, different applications require the accurate knowledge of the cross sections for all of them in a large range of impact energies and for different combinations of projectiles and targets. Most often the cross sections are just the seed for large scale simulations of the  penetration of ions in solids or biological matter. Therefore what is needed at some stage is the availability of accurate models which at the same time give rise to fast codes for the computation.   Generally, the theoretical studies of single electron capture involving many electron targets  have been performed within the framework of IEM.  In this approach, a  given active electron evolves independently of the  others (the passive ones) in an effective  target  potential due to the Coulomb field of the nucleus  screened by a static potential originated by them.  The use of IEM requires an accurate single particle model  potential to represent the interaction between the active electron  and the  residual target.   Different distorted wave models  have been developed to study single electron capture  in ion-atom collisions at intermediate and high impact energies, where perturbatives  models  provide a good description of the process. In order to study K-shell vacancy production in asymmetric collisions, the Continuum Distorted Wave-Eikonal Initial State (hereafter refer to as CDW-EIS) approximation was introduced by Martínez et al. [1].  In this approximation, the final electronic bound wavefunction is distorted by an effective coulomb continuum factor associated to the active electron-residual target interaction. In the initial channel, infinite multiple scattering terms associated with the active electron-projectile potential are considered through an eikonal phase which multiplies the target bound state, represented by a Rothaan-Hartree-Fock wavefunction.   Recently, Abufager et al. [2] presented an improved version  of the three-body CDW-EIS model, obtained by  considering an  active electron-residual target Hartree-Fock-Slater model potential in both the initial and final channels, as it was done previously for CDW approximation [3] . In this new model (hereafter refer to as GCDW-EIS),  the initial bound state wavefunctions and final continuum factors were obtained from the numerical resolution of the corresponding Schrödinger equations.   In this work we present  theoretical results obtained by using the generalized GCDW-EIS   approximation, for the  single electron capture reaction corresponding to impact of bare ions on He, Ne and Ar targets. We focus our attention on the contributions to the total cross sections coming from the different  shells of the target.  Differential cross sections for single electron  capture in H+ + He collisions at  high impact energies are also analyzed. GCDW-EIS results are compared with  theoretical calculations obtained using  the CDW-EIS model,  in order to determine the importance of the description of the bound and continuum target states in the  entrance and exit channels, respectively. Other theoretical results  and  experimental data are also presented.   References 1- Martínez A E, Deco G R, Rivarola  R D and Fainstein P D  1988  Nucl. Instrum. Methods B  34  32. 2- Abufager P N, Martinez A E, Rivarola R D and Fainstein P D 2004   J. Phys. B  37 817. 3- Gulyás  L, Fainstein P  and Shira  T  2002  Phys. Rev. A   65  052270.