[en] We investigate the orientation dependence for multiple electron transfer in collisions of slow highly charged ions with rare gas dimers. For this purpose, we modify the previous three-center Coulombic over-barrier model for the target of covalent bonding molecules, so as to take full account of three-center nature in electron dynamics during a collision. The model developed is applied to the collisions of A⁸⁺+Ne₂, where charge state distributions are derived for Coulomb explosion fragments. The distributions are predicted to be qualitatively different for parallel and perpendicular molecular orientations with respect to the ion beam; fragment ion pairs with symmetric charges are dominant when parallel, while asymmetric charges when perpendicular. This result is in sharp contrast to that for covalent molecules, reflecting electron localization at atomic centers in rare gas dimers

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[en] We investigate the excitation of a hydrogen-like ion from 1s state to 2s by simultaneous two-electron impact at subthreshold incident energies, as an example of three-body scattering, in which three particles enter and three emerge. The excitation rate is roughly estimated with the second-order Born approximation in terms of the long-range dipole interaction between an electron and an ion. In most cases, the rate for the ion is found to have the order of magnitude of < approx 10^-25n²/Z⁸ sec^-1, where n denotes the electron number density (in cm^-3) and Z, the nuclear charge of the ion. Those values may be too small to be detectable in ordinary beam experiment, though they are found to be comparable to the geometrical cross section introduced for three-body collision. We also discuss the effects of the double-scattering singularity of the transition amplitude. (author)

[en] Coupled channel analysis is performed for anomalous inelastic scatterings (₁₈O,sup(18)O* (2⁺,1.98MeV)) from sup(58,60,62,64)Ni and ₉₂Mo with the incident energy slightly above the Coulomb barrier. The coupling form factors are constructed by the sum of the valence and the core polarization part as was done by Landowne and Wolter. Inclusion of the valence part makes channel coupling effects appreciable. The reorientation effect and readjustment of the distorting potential are found to be very important. The theoretical results reasonably well reproduce the experiments from sup(58,62)Ni and ₉₂Mo, but strong isotope dependence remains unsolved. (author)

[en] A classical field-ionization model is developed for sequential multiple ionization of diatomic and linear triatomic molecules exposed to intense (∼ 10¹⁵W/cm²) laser fields. The distance R_ion of Coulomb explosion is calculated for a combination of fragment charges, by considering nonadiabatic excitation followed by field ionization associated with the inner and outer saddle points. For diatomic molecules (N₂, NO, and I₂), the model explains behaviors observed in experiments, as R_ion(21→31) < R_ion(21→22) between competing charge-asymmetric and symmetric channels, and even-odd fluctuation along a principal pathway. For a triatomic molecule CO₂, a comparison of the model with an experiment suggests that charge-symmetric (or nearly symmetric) channels are dominantly populated. (author)

[en] We develop a classical model of an ideally sudden character for vibrational and rotational excitations in collisions of an atom (or an ion) with a diatomic molecule at energies as high as 10-10² eV. The energy-loss spectra with vibrotational levels left unresolved are analytically expressed with a repulsive intermolecular potential in a hard potential limit (i.e., a vanishing range of force). It turns out to be an extension of the hard shell model for a rigid-rotor molecule developed by Beck et al. two decades ago. For a homonuclear molecule, the hard potential model generally derives spectra with double peaks at both edges, one nearly elastic and another deeply inelastic. They are analogous to rotational rainbows though their positions are affected by vibrational excitation. Classical trajectory calculations with a finite-range model potential are carried out for collision systems of H⁺+N₂ and Li⁺+N₂, and systematically compared with the model. It is found that the effect of vibrational excitation manifests itself the way the model predicts. It is also demonstrated that the spectra are virtually reduced to the hard potential model when the vibrational period is artificially taken much longer than a collision time, while reduced to the hard shell model when much shorter

[en] The energy-loss spectra in large-angle Li⁺+N₂ scatterings are analyzed with the hard-potential model recently proposed, along with the previous hard-shell model. The respective roles of rotational and vibrational excitations are revealed through systematic comparisons of experimental spectra with the models in a wide range of energies (8-100 eV) and angles (40 deg. -120 deg.). The effect of vibrational excitation is found to manifest itself in the shifts of double peaks. Their energy dependence is accounted for by the shape of the equipotential surface as well as by the vibrational suddenness in a collision. The peak position is shown to be sensitive to the curvature of the surface at the orientation angle of 90 deg., hence to the three-body potential. The unacceptable result of a previous semiclassical calculation is suggested to come from the inappropriate potential taken

[en] A theory of channel coupling array is developed for rearrangement reactions in Coulomb three-body systems. Inhomogeneous coupled differential equations for the three Faddeev components are derived and directly solved with the technique of complex rotation in the exterior region. This method is applied to slow antiproton collisions with hydrogen atoms. It is found for a collision energy of 6.8 eV that the antiproton is captured dominantly into protonium states with the principal quantum numbers around 40 and that the electron is released with energies around 2 eV. The electron velocity thereby obtained is much higher than the incident velocity of the antiproton. Time-dependent wave-packet propagation of the Faddeev components is also investigated to illustrate the peculiar dynamics

[en] A nontrivial electron stereodynamical effect recently found in Coulomb explosion of N₂ molecules with slow (20 - 200 eV/amu) Kr⁸⁺ ions is investigated. We analyze a population asymmetry observed in charge-asymmetric recoil ion pair distributions associated with the left and right projectile scatterings. The three-center Coulombic over-the-barrier model is developed so as to describe a whole collision process as formation of a triatomic quasi-molecule and its decay into three moving atomic ions. The asymmetry measured is well explained in the present model where two-step electron localization is crucial. (author)

[en] The three-center Coulombic over-the-barrier model is developed for Coulomb explosion of a homonuclear diatomic molecule in collisions with a slow (∼10 eV/amu) highly charged ion. A conventional two-step picture of multiple electron transfer followed by Coulomb explosion is far from appropriate because the molecule sets out to dissociate before the incident ion approaches the closest distance. We treat the formation of a quasi-molecule and its decay into the three moving atomic ions. Charge-asymmetric population between fragment ions observed in a triple-coincidence measurement is suggested to reflect the bond elongation during a collision. Collisions of Kr⁸⁺ + N₂ are analyzed. (author)