[en] Total double- and single-charge transfer cross sections are calculated for the collisions of C⁶⁺ ion with He atom in the impact energy region 0.1 ≤ E ≤ 10 keV/amu. The perturbed-stationary-state method in the impact parameter approximation is used with a basis set of SCF-CI molecular orbitals. There are many curve crossings among the adiabatic potential curves. A diabatic treatment is, however, found to be useful for the most of curve crossings. The single-charge transfer mainly occurs through the avoided crossing near 5 au, while the double-charge transfer takes place via a two-step one-electron transfer or a direct process. Hence the double-charge transfer cross section obtained (∼ 10^-16 cm²) is about a tenth of the single-charge transfer cross section in these impact energies. (author)

[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

[en] Total charge transfer cross sections are calculated for the collisions of Li³⁺ and Be⁴⁺ ions with H(1s) atoms in the low energy region (E lt 25 keV/amu). The perturbed-stationaly-state method in the impact parameter approximation is used with a basis set of adiabatic one-electron two-center molecular orbitals. For the Li³⁺-H system, a reasonable agreement is found between the present calculation and the recent experiment. (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] 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] Multiple ionization dynamics of rare gas dimers by slow highly charged ions is investigated with the three-center Coulombic over-barrier model. Quasi-molecule formation of an electron at the distant atomic site from the projectile is shown sensitive to partial screening of ion-core charged at the near atomic site due to electrons already forming quasi-molecules. It is found that the screening effect suppresses simultaneous chained electron removal from both sites and hence enhances charge-asymmetric ion pair formation. The ion pair distribution measured in Ar"9"+ + Ar_2 collisions is well reproduced by taking a screening factor of s = 0.4 in the model. (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)

[en] The three-center Coulombic over-the-barrier model is developed for the 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 BC sets out to dissociate before the ion A approaches the closest distance. We treat the formation of a quasimolecule ABC and its decay into the three moving atomic ions, where two possible processes are considered for population in an atomic site B as ABC → BC → B and ABC → AB → B. It is shown that the contribution from the second process is crucial in a slow collision. Charge-asymmetric fragmentation between sites B and C observed in a triple-coincidence measurement is suggested to re.ect the bond elongation during a collision. Collisions of Kr⁸⁺ +N₂are analyzed

[en] Multiple ionization dynamics of rare gas dimers by slow highly charged ions has been investigated using the three-center Coulombic over-barrier model. The outermost electrons at two atomic sites in the dimer are sequentially removed by forming a quasi-molecule with a projectile, where partial screening is taken into account in the non-active site ionized during a collision. It is found that the fragment ion pair (Q,Q′) distribution is remarkably sensitive to the screening effect, which enhances the population of highly charge-asymmetric pairs such as (2,0) and (3,1). Recent measurement of the ion pair distribution in Ar⁹⁺ + Ar₂ collisions is best reproduced with the present model by taking a screening parameter of s = 0.4. (paper)

[en] We investigate a nontrivial asymmetric population observed in a triple-coincidence measurement for charge-asymmetric Coulomb explosion of N₂ molecules in collisions with a slow (10 - 100 eV/amu) Kr⁸⁺ ions. The three-center over-the-barrier model is developed to describe collision dynamics including many active electrons as the formation of a triatomic quasi-molecule and its decay into three moving atomic ions. The present model predicts an asymmetry effect consistent with the measurement, where molecular bond elongation during a collision is crucial. Electron localization processes in the quasi-molecular decay are examined in detail in relation to two saddle points in the three-center Coulomb potential.