State-selective electron capture by 18-keV Kr8+ ions from laser-excited Rb*(15p-25p) Rydberg atoms.

Abstract

State-selective single electron capture, in collisions of multicharged ions ${\mathrm{Kr}}^{8+}$ at 18 keV with laser-excited Rydberg ${\mathrm{Rb}}^{\mathrm{*}}$(${\mathit{n}}_{\mathit{ip}}$) atoms, is investigated by use of a field ionizing lens system (FILS), in a three-crossed-beam experiment. By scanning the laser over a wide range of wavelengths (303--298 nm), this investigation covers the 15p--25p Rydberg series, showing the influence of the initial state of Rb. For every well-defined ${\mathrm{Rb}}^{\mathrm{*}}$(${\mathit{n}}_{\mathit{ip}}$) state, (i) very high Rydberg states of the ${\mathrm{Kr}}^{7+\mathrm{*}}$(n) product ions are detected as a consequence of the high degree of excitation of the target and of the high charge of the projectile, and (ii) the n distribution of the capture cross section is obtained in the domain 67\ensuremath{\le}n\ensuremath{\le}95, by measuring the energy spectrum of the ${\mathrm{Kr}}^{8+}$ ions produced by field ionization in the FILS of the excited product ions ${\mathrm{Kr}}^{7+\mathrm{*}}$. These n distributions become wider and are systematically shifted towards higher n values as ${\mathit{n}}_{\mathit{i}}$ increases. By using the classical trajectory Monte Carlo method, the n distributions are calculated for the ${\mathit{n}}_{\mathit{ip}}$ series. Although the calculated n distributions are systematically wider, the behavior of their widths and of their relative positions is in agreement with the experiment. On the other hand, the extended classical over-the-barrier model yields n distributions significantly narrower than the experimental ones. \textcopyright{} 1996 The American Physical Society.