[en] Neutralization of low keV Ne⁺ ions at a LiF(001) surface is studied in a grazing incidence geometry. The combination of energy loss and electron spectroscopy in coincidence reveals two neutralization channels of comparable importance. Besides the Auger process, the Ne⁺ neutralization can proceed via peculiar target excitation, corresponding to the formation of an electron bihole complex termed trion

[en] We have recently shown that the large energy loss experienced by slow protons interacting with a LiF surface is primarily caused by the population of surface excitons [11]. These states are most probably populated by electron transfer from H^- ions formed at halogen sites, whereas secondary electron emission results from direct detachment of the negative ions in collisions with halogen sites. We report here on the impact energy dependence of the charge-state of the scattered projectile, its energy loss and the associated electron yield. From these complete measurements, the transfer probability to the surface excitons and its dependence upon impact energy is derived in the range 0.6-10 keV

[en] Measurement of the three dimensional anisotropic Auger electron emission from excited projectiles can provide the complex amplitudes (magnitudes and relative phases) for the magnetic substates, formed in double electron capture collisions. Done in coincidence with position sensitive detection of the scattered projectiles, one obtains the scattering angle dependences of the complex amplitudes. The first such measurements were reported recently for C⁵⁺ + He collisions; here the authors report on the similar system B⁴⁺ + He at 20 keV collision energy (v=0.27 au). Measurements of this kind are the most detailed available for slow, multiple electron capture collisions. Results will be presented for 1s2s²²S, 1s2s2p ²P and 1s2p²²D terms of B²⁺ in comparison with those for the same states of C³⁺ formed in the C⁵⁺ + He collision

[en] The grazing angle interaction of 2 keV Ne⁺ projectiles with a LiF(0 0 1) surface is studied with the combination, in coincidence, of projectile and electron time-of-flight spectroscopy. The measurements reveal that besides the standard Auger neutralization process that leads to electron ejection, there is another neutralization mechanism that does not result in electron emission. The latter process has been identified as the formation of an electron-bihole complex termed trion. We report here the detailed study of the scattering angle dependence of these two neutralization channels, with comparison with the process leading to population of surface excitons

[en] We have measured the production of low-energy (∼0-10 eV) electrons coincident with the final projectile charge states, O^q+, from 80 keV O⁸⁺ collisions with He and Ar targets. For the He target, we confirmed our earlier observation that virtually all low-energy electrons emitted in the direction of the projectile are associated with O⁷⁺ ions, i.e. no electrons are observed coincident with the O⁸⁺ final state. For the Ar target, the results are similar and more complex. Here the fraction of electrons coincident with the O^8,7,6,5+ final states are approximately 0, 30, 20, and 1%, respectively. Thus, the three-electron process yielding O⁶⁺ is nearly as strong as the two-electron one yielding O⁷⁺, and there is evidence for a four-electron mechanism (O⁵⁺ channel) as well

[en] We present high-resolution electron spectroscopy studies of the interaction of hydrogen-like nitrogen and oxygen ions with a thin-film covered Au(1 1 1) surface. As coverages LiF and C₆₀ are used to investigate the interplay between the projectile and the surface electronic structure. The results from LiF permit a definite conclusion on the respective role of the band gap and the binding energy in bulk LiF during the projectile neutralization and relaxation. Results from C₆₀ raise new questions on the actual nature of the processes responsible for the filling of the projectile L-shell

[en] The authors have used cold target recoil ion spectroscopy to study collisions of slow (v ∼ .40 au) He²⁺ and O⁶⁺ ions with He atoms. The results include differential scattering cross sections for state resolved electron capture channels and target ionization. With He²⁺ projectiles, single capture yielding He⁺ ions in their ground states, shows marked oscillatory structure in the angular scattering (the first such observation for this channel in the quasimolecular regime). With O⁶⁺ projectiles, longitudinal momentum spectra (energy open-quotes gainclose quotes) of He²⁺ recoil ions coincident with O^4,5+ products, show nonequivalent electron final states in the true, and autoionizing, double capture channels. The differential cross sections for these channels bear on the relative importance of single transfer at two vs double transfer at one avoided crossing in the transient quasimolecule

[en] Grazing interaction of low energy protons with LiF(1 0 0) is studied using a new coincidence technique combining energy loss, charge state analysis and electron spectroscopy. Correlation between the scattered projectile energy loss and the number of emitted electrons points to an energy loss mechanism not leading to electron emission. Detailed analysis of the energy loss spectra, which show well-resolved structures, suggests that this mechanism corresponds to the population of surface excitons. Moreover the correlation between the projectile final charge state and the number of emitted electrons sheds new light on the major role played by the negative ion at the surface. Electron removal from the valence band proceeds mainly through formation of H^- at halogen sites, whereas electron emission results from the detachment of these negative ions at subsequent F^- sites

No abstract available

[en] Fullerene ions, C₆₀^q+, with q up to 9, have been observed in a study of their production by slow (v<0.5 au) impact of the projectiles ⁴⁰Ar^{4,5,8,12,16,17+}, ¹³⁶Xe²⁷⁺, ⁸⁶Kr²⁸⁺, ²⁰⁹Bi^20,38,44,46+, and ²³⁸U⁴⁶⁺ on a neutral fullerene beam. The distribution of ion yields for each projectile is representable by a binomial form; variation of the biniomial fit parameters with projectile charge suggests the maximum positive charge for the fullerene ion. Correlations between the time of flight of first and second ions are shown to provide details of the fragmentation of fullerenes in close collisions. copyright 1996 The American Physical Society