[en] Hydrogen ionization in soft collisions with relativistic charged projectiles is considered for the ranges of parameters: (a) v < or approx. Z<< v^2γ, v₀<< v< c; (b) Z<< v, v₀<< v< c (here Z is the projectile charge, v the collision velocity, v₀ the Bohr velocity in the hydrogen ground state, γ the Lorentz factor and c=137 is the speed of light). Analytical expressions have been obtained for differential cross sections of hydrogen ionization accompanied by the emission of soft electrons. It is found that the electric-dipole interaction contributes most to the soft emission. An asymmetry in the angular distribution of soft electrons is found which can be interpreted as a result of two effects: (i) an absorption of virtual photon momenta by the atomic system, (ii) so-called 'post-collision interaction'. These results are generalized to describe analytically soft-electron emission from helium colliding with relativistic projectiles. This generalization gives a simple fit to experimental data on both differential and total cross sections for helium single ionization in a wide range of projectile charges and velocities. (author)

[en] Photoionization of an atom via interatomic correlations to N neighboring atoms may be strongly enhanced due to constructive interference of quantum pathways. The ionization proceeds via resonant photoexcitation of a neighbor atom and subsequent interatomic Coulombic decay. The enhancement can scale with N², leading to ''superenhanced photoionization.''

No abstract available

No abstract available

[en] The neutralization of negative hydrogen ions in collisions with fast (including relativistic velocities) highly charged projectiles is considered by using a simple approach resulting in analytical cross sections for the range of parameters where the Born approximation is invalid. A formula has been derived for the cross section of H^- neutralization. (author)

[en] We have measured the dependence on the molecular orientation of the cross section for two-electron transfer from hydrogen molecules to fast (1.2 and 2.0 MeV kinetic energy) He''2''+ ions. A very strong angular dependence is found, where the maximum and minimum cross sections differ by more than a factor of three. Further the angular dependencies are markedly different for the two different projectile energies. The variations are explained as resulting from the interference of two waves describing projectiles neutralized in the proximity of either of the two target protons. The molecular axis orientation determines the phase difference of these two waves and thereby affects the cross section.