Experimental Investigation of Two-Electron Processes in Ion-Atom Collisions

Abstract

This paper will cover two separate mechanisms currently being investigated in collisional atomic physics. The first mechanism, which is the main focus of this paper, is a double electron process investigated for the collisions of iron (26FeQ+, q=23-25) ion projectiles and molecular hydrogen (H2). This double electron process, which rises from one ion-atom collision, involves single electron capture by the projectile accompanied by simultaneous electron excitation. This combined capture and excitation results from electron correlation, meaning that it is a process resulting from the interaction between the two participating electrons. The simultaneous occurrence of these events is equivalent to an inverse Auger transition. The Auger process is a nonradiative atomic deexcitation mechanism which comes about due to the energy degeneracy of excited states. The correlated two-electron process discussed, like the Auger process, is resonant for certain relative electron energies and has been given the name of resonant transfer and excitation (RTE)4. The second mechanism to be discussed has been given the name of transfer ionization (TI). While the RTE process was concerned with collision events in respect to the projectile ion, the TI process is investigated by observing the events pertaining to the target atom. TI involves a combination of electron capture with an additional target ionization. In other words, the target atom loses two electrons, only one of which is transferred to the projectile. This process will be investigated through collisions between ionized helium (He+) and neutral helium (He). Therefore, in this case, the TI process only occurs when the helium atom target loses both of its electrons.