No abstract available

No abstract available

[en] A new type of multicoincidence technique, that simultaneously handles 64 channels is used to carry out a detailed investigation of the He(n = 2) excitation in He-He collisions. Processes leading to formation of metastables are studied using recoil-scattered-particle coincidence measurements, while He(2¹P) excitation processes are investigated by photon-scattered-particle coincidences. The magnetic sublevel population for the He(2¹P) excitation is determined from the angular correlation between the photon and the scattered particle. The data are discussed in the framework of the independent-electron quasi-molecular model. One-electron excitation is consistent with the model but for two-electron excitation, effects are found which cannot be accounted for within the independent-electron picture. (author)

[en] The ''multicoincidence technique'' results from the combination of two experimental methods which are widely developed in atomic physics, namely the ''position sensitive detection'' and the coincidence technique. This new technique which actually consists in taking coincidence data in several channels, simultaneously, combines the advantage of both methods reduction of data acquisition time and more accurate identification of the various processes occurring in a collision. The purpose of this paper is to describe the electronic devices developed by various authors and to compare their relative performances and limitations. Applications to atomic collisions are exemplified. (Auth.)

[en] An experimental and theoretical investigation of the He⁺-H collision is performed. Identification of the elastic process and direct excitation of the H atom is obtained by measuring the characteristic energy losses undergone by the scattered He⁺ whereas time-of-flight (TOF) technique is used to study the electron capture processes. Differential cross sections are measured in the 750 to 2500 eV energy range. The interpretation makes use of a simple independent electron model. All excitation processes are seen to be induced by a common primary 2psigma-2pπ rotational coupling. The sharing of the excitation between H(2p) and He(1s2p) is induced by a long-range coupling. Using this model and previously calculated potentials, the differential and total cross sections are calculated with a semi-classical method. In particular structures in the total cross sections are discussed. A reasonable agreement is found between theory and experiment. (author)

No abstract available

[en] The production of H₂ neutral molecules in collisions between H₂⁺(X) and Na(3s, 3p) has been investigated in the 0.25-2 keV energy range using the time-of-flight spectroscopy. In the collision with the ground-state target the population of the H₂ states B¹Σ _u⁺ and c ³Π_u^- has been observed. In the charge exchange with laser-excited sodium the states C¹Π_u and E, F ¹Σ_g⁺ are found to be populated. The investigated electron transfer process is strongly forward scattered and the relative total cross sections σ_3p/σ_3s for the production of H₂ bound states are found to vary between five and two in the explored energy range. (author)

[en] Recent progress in the experimental investigation of atomic collisions at keV energies involving a polarized excited target is reported. The role of initial orbital alignment and orientation in electron capture and electron detachment processes is addressed. The H⁺-Na(3p) collision is chosen as a prototype for non resonant charge transfer in a quasi-one-electron system, as is the H^--Na(3p) collision for electron detachment from a state of controlled symmetry. Strong alignment and orientation effects observed in total and double differential cross sections are reported and discussed. (Author)

[en] We have performed an experimental study of the electron transfer processes in Li⁺-Na(3s) collisions leading to Li(2s) and Li(2p), using ⁶Li⁺ beam at a collision energy of 1 keV. Neutral particles scattered in a narrow forward cone were detected in coincidence with polarization-analysed photons emitted from the Li(2p) state. This technique enabled determination of the complete Li(2p) transition matrix as a function of scattering angle, which is typically a fraction of a degree. The experimental results for the complete set of differential cross sections and coherence parameters are in excellent agreement with the predictions of recent molecular basis coupled-channel calculations of Machholm and Courbin. (author)

[en] This paper reports experimental and theoretical P-state-to-P-state results for the electron transfer process Li⁺+Na(3p)→Li(2p)+Na⁺ at an impact energy of 1 keV. By a systematic combination of the optical preparation of specific Na(3p) states with Stokes parameter analysis of the resulting Li(2p) state, we extract detailed information on scattering amplitudes and the underlying collision dynamics of the electron transfer process. Eight out of the nine independent parameters characterizing a 'complete scattering experiment' have been extracted. Coupled channel results for the state-to-state transfer probabilities and differential cross sections have been derived using a two-centre atomic orbital basis. The overall agreement is good between the experimental observations and theoretical predictions, as well as with the molecular orbital basis results of Machholm et al (Machholm M, Lewartowski E and Courbin C 1994 J. Phys. B: At. Mol. Opt. Phys. 27 4681). Based on this agreement and our theoretical results for the velocity dependence, we address the general concepts of propensity rules for alignment and orientation effects in P-state-to-P-state electron transfer. (author)