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[en] Recently it was pointed out that electron capture occurring in fast ion-atom collisions can proceed via a mechanism which earlier was not considered. In the present paper we study this mechanism in more detail. Similarly as in radiative capture, where the electron transfer occurs due to the interaction with the radiation field and proceeds via emission of a photon, within this mechanism the electron capture is caused by the interaction with another atomic electron leading mainly to the emission of the latter. In contrast to the electron-electron Thomas capture, this electron-electron (E-E) mechanism is basically a first-order one having similarities to the kinematic and radiative capture channels. It also possesses important differences with the latter two. Leading to transfer ionization, this first-order capture mechanism results in the electron emission mainly in the direction opposite to the motion of the projectile ion. The same, although less pronounced, feature is also characteristic for the momenta of the target recoil ions produced via this mechanism. It is also shown that the action of the E-E mechanism is clearly seen in recent experimental data on the transfer ionization in fast proton-helium collisions.

[en] Resonant two-photon single ionization in a system consisting of two spatially well-separated identical atoms is studied. Because of two-center electron-electron correlations, the ionization may also proceed through photoexcitation of both atoms with subsequent interatomic Coulombic decay. We show that this channel may qualitatively change the dependence of the photoionization on the field intensity as well as the spectra of emitted electrons.

[en] The theory of electron loss from projectile-ions in relativistic ion-atom collisions is extended to the case of collisions with excited atoms. The main feature of such collisions is a resonance which can emerge between electron transitions in the ion and atom. The resonance becomes possible due to the Doppler effect and has a well-defined impact energy threshold. In the resonance case, the ion-atom interaction is transmitted by the radiation field and the range of this interaction becomes extremely long. Because of this the presence of other atoms in the target medium and the size of the space occupied by the medium have to be taken into account and it turns out that microscopic loss cross sections may be strongly dependent on such macroscopic parameters as the target density, temperature and size. We consider both the total and differential loss cross sections and show that the resonance can have a strong impact on the angular and energy distributions of electrons emitted from the projectiles and the total number of electron loss events

[en] We show that the derivation of the approximate solution for the motion of an unbound electron in the simultaneous presence of the Coulomb field and a circularly polarized plane wave given in Reiss and Krainov Phys. Rev. A 50, 910(R) (1994) contains an error caused by confusing the space coordinates before and after the Kramers-Henneberger transformation

[en] We consider radiative recombination and photoionization in an atomic system, which consists of two subsystems A and B. These subsystems are well separated in space and it is supposed that A has a lower ionization potential. In such a case photoionization of A and recombination of an incident electron with A⁺ can be strongly influenced, via two-center electron-electron correlations, by resonant electron dipole transitions induced in B. A theoretical description of these two-center resonant dielectronic processes is presented.

[en] We consider two-centre dielectronic transitions occurring in collisions of fast highly charged hydrogen-like projectiles with neutral atomic targets. In such collisions, in addition to the reaction channel due to the two-centre electron-electron interaction, the reaction channel induced by the two-centre electron-nucleus interactions becomes important. We show that the account of distortions of initial and final states of the target caused by the field of the projectile nucleus (which can also be viewed as imposing the Coulomb boundary conditions on these states) leads to an approach in which both these reaction channels are combined in a natural and relatively simple way. As a result, this approach enables one to extend calculations of different cross sections for two-centre dielectronic transitions from the high-velocity to the intermediate-to-high collision velocity regime

[en] We consider ionization of helium targets by impact of highly charged projectile ions in collisions at relativistic energies. The overwhelming majority of electrons emitted in such collisions have velocities in the target frame, which are much less than the speed of light. Therefore, considering the collisions in this frame we treat the electron dynamics nonrelativistically. The projectile-target coupling in the collision is described within the symmetric eikonal approximation taking explicitly into account the interaction between the projectile and all the target constituents. The relation between the symmetric eikonal and the first Born approximation is discussed in detail. Helium single ionization is considered by developing an effective three-body (projectile, 'active' electron, target core) model of this process in which (undistorted) initial and final states of the 'active' electron are described in a Hartree-Fock approximation. Using a four-body model we also briefly discuss the contribution to single ionization from simultaneous ionization-excitation. A good agreement with available experimental data has been found

[en] We present an eikonal model for electron excitation and loss from highly charged ionic projectiles colliding with atomic targets at relativistic collision energies. In this model the distortion of the target transition four-current by the strong field of the projectile nucleus is taken into account using the symmetric eikonal approximation. General expressions are derived for the eikonal transition amplitude in the case of collisions with one- and two-electron targets. The correspondence between the eikonal and first-order transition amplitudes is discussed. Relativistic features and the nonrelativistic limit of the eikonal transition amplitude are considered. It is shown that the higher-order terms in the projectile-target interaction, which are not accounted for by the first-order amplitude, may be of importance even for quite small values of ν=Z_p/v, where Z_p is the charge of the projectile nucleus and v the collision velocity

[en] We consider one-photon ionization in a system consisting of two different atoms, A and B, which are well separated in space. In such a case, photoionization of the atom with a lower ionization potential can be very strongly influenced, via two-center electron-electron correlations, by resonant electron dipole transitions induced in the other atom. We present a detailed consideration of this resonant photoionization process and discuss a number of effects that are inherent to it.