Ionization and Electron Capture by OXYGEN(8+) from Aligned Molecular Deuterium

Velocity space distributions of deuterons from electron capture and ionization by bare oxygen ions of energies from 2 to 16 MeV in collision with molecular deuterium targets were measured. The experiment was performed by applying an extraction electric field perpendicular to the beam axis to project the whole velocity distribution of the recoil ions onto a two-dimensional position sensitive detector. By additional measurement of the time-of-flight of these recoil ions, we were able to reconstruct the three -dimensional velocity distribution. From the reconstructed results, the dependence of the cross sections on the alignment of the molecular axis with respect to the beam axis was determined. The results show that in the case of transfer ionization and transfer excitation, the deuterium molecules are more likely to be in the states of orientation perpendicular to the incident beam than parallel to the beam. This feature can be qualitatively interpreted by the theory as resulting from the interference of capture amplitudes from the two atomic centers. When the molecular orientation is perpendicular to the beam, the phase difference between amplitudes originating on the two scattering centers of the molecule is minimum resulting in constructive interference. In the case of double ionization and ionization excitation, little orientation dependence was observed.