H. Jouin

Total and partial cross sections of electron transfer processes with hydrogen gas targets: Be4+ + H2

We report the implementation of programs to treat electronic transitions in ion-molecule collisions and the calculation of vibrationally-resolved partial cross sections. This includes the ab initio calculation of non-adiabatic couplings, the implementation of a block-diagonalization procedure, and the evaluation of vibrational transition probabilities. Using a two-state basis, we present some preliminary results on the Be4+ + H2(v = 0, L = 0) Be3+(3l) + H2+(v, ΣLM) reaction. These show that for nuclear velocities v < 0.2 a.u. vibration cannot be ignored, even though anisotropy effects are small. The reason is the strong dependence of the electronic transition amplitudes on the H–H distance.

Screening models for laser–cluster interactions

We study the applicability of various screening approaches within the context of laser–cluster interactions. Comparisons between well-known screening models, such as the static screened Coulomb, Debye–Huckel, Thomas–Fermi and ion–sphere ones, and a more elaborated approach based on the Lindhard dielectric function within the linear response theory (Gupta and Rajagopal 1982 Phys. Rep. 87 261) show that none of the simpler classical models can be used through the complete range of plasma situations encountered in laser–cluster interactions. Therefore, we have clearly specified the validity domains of the various models as well as the regions of electronic temperature and density where Friedel oscillations appear.

Single- and double-electron capture in low-energy Ne10+-He collisions

We present a combined experimental/theoretical study of Ne10+-He collisions in the 50?E?150?keV impact energy range using improved-resolution recoil ion momentum spectroscopy. Total and differential cross sections for single-electron capture onto the levels n = 3,4,5 and 6 of Ne9+(nl) and double-electron capture onto series of doubly excited states 3, n and 4, n with n = 4, 5 and 6 of Ne8+ have been obtained. They are found to be in good agreement with close-coupling calculations. Population mechanisms for the dominantly populated double-capture channels have been deduced from this work. Special emphasis is brought to the analysis of the partial stabilization ratios to obtain a new insight into the velocity dependence of total stabilization ratios.

Atomic distortion effects for surface-plasmon-mediated proton neutralization

Abstract We obtain the energy shifts and perturbed wavefunctions for the ground state of a hydrogen atom near a Mg surface and apply them to analyze the effects of the atomic distortion on the process of proton neutralization at metallic surfaces by surface-plasmon emission. The distorted collective transition rates are noticeably larger than the unperturbed rates mainly due to the energy shifts of the atomic level. We also analyze the possibility of the appearance of a threshold surface–atom distance below which the collective rates might vanish as a consequence of the upward shift of the perturbed atomic energy level.

Quantal and semiclassical calculations of charge transfer cross sections in + H collisions for impact energies of

Total and n-partial cross sections for charge transfer in collisions are calculated for collision energies between and . A molecular expansion is employed, and semiclassical and quantal calculations are carried out including a common translation factor and a common reaction coordinate, respectively. The comparison between quantal and semiclassical cross sections and transition probabilities is discussed.

Plasmon dispersion effects for surface plasmon mediated proton neutralization at Mg surfaces

Abstract Transition rates for surface plasmon-assisted electron capture by H+ ions interacting with Mg surfaces have been calculated. We show that the plasmon dispersion and the representation of the initial metal state significantly change the transition rates with respect to previous calculations. In particular, the ion perturbation on the initial state greatly increases the transition rates at large ion–surface distances which is consistent with the results obtained by other authors for the Auger process.

Model potential treatment of C4+ + H2 collisions at low impact energies

We present cross sections for electron capture in C4+ + H2 collisions in the energy range 50 eV amu-1≤E≤ 6 keV amu-1, calculated using a model potential aproximation to treat the interaction of the active electron with C4+ and H2+ cores and an equivalent-electron bielectronic interpretation of the probabilities. The limitations of this method are analysed by comparison with the two-electron ab initio treatment. Double-electron-capture cross sections are also calculated using ab initio and model potential treatments. We propose a modified independent particle model to evaluate single-electron-capture cross sections.

Study of core effects for partial cross sections σnl in the keV energy range

Abstract We have calculated partial cross sections σnl for collisions between highly charged ions and atomic targets in the keV energy range. The corrected PSS approximation has been used with an appropiate form of the common translation factor. From the comparison between the results for bare and nonbare nuclei of the same charge on the same target, we have investigated the competition between the Stark effect and the core electron interaction. For instance at low energies (ν

Molecular treatment of H+ + H− collisions at intermediate energies

Abstract A one-electron model potential approach is used to evaluate total one electron-loss cross sections in H + + H − collisions. Results employing a minimal basis set shows an accumulation of population in the charge exchange channel similar to those obtained for the He 2+ + H collisions.

Molecular data for the hydrogen quasimolecule using a one-electron model

We test the validity of one-electron models for homonuclear diatomic systems by a study of the molecular energies and dynamical couplings that are relevant in the treatment of H++H- collisions. We also present the modifications introduced in the couplings by a common translation factor that has proved suitable at high impact energies.