On the detection of two electrons in low-lying continuum states of a single projectile ion resulting from the collision of a 10.7 MeV AG4+ ion with an AR gas target

An important problem in atomic dynamics which may require treatment beyond the independent particle model is the structure of high energy doubly-excited states, in which two electrons are simultaneously excited away from the rest of the electrons in the ionic core, making their mutual interaction as important as their individual interaction with the remaining core. This thesis reports on an atomic collision experiment which investigates the feasibility of using a large 30° parallel plate electrostatic analyzer to detect two electrons in low lying continuum states of a projectile ion. The two electrons are excited just above the double ionization threshold of a Ag^q+ projectile ion in a collision of a 0.1 MeV/u Ag⁴⁺ ion with an Ar atom. The analyzer is used to deflect the free electrons which move with approximately the projectile velocity into a detector. The electron detector consists of electrically isolated anode segments located behind a microchannel plate electron multiplier. We have measured the cross sections for producing states with one electron moving with a kinetic energy less than 0.13 eV in the projectile frame and the other moving with somewhat higher kinetic energy. To the best of our knowledge the present work describes the first sucessful measurement of this kind. The results of our measurements may signal electron-electron correlation effects. We have shown that electrons moving with kinetic energies between 0.18 eV and 0.35 eV in the projectile frame are more likely to move perpendicular than antiparallel to the beam direction if another very low energy continuum electron is present. Otherwise the angular distribution of the electrons, in this energy range, is more isotropic.