Resonant transfer excitation: Interference effects

Interference effects in RTE (Resonant Transfer Excitation) can be studied for low Z projectiles via Auger electrons emitted from highly ionized fast moving projectile ions following collisions with low Z targets. RTE in ion-atom collisions is closely related to dielectronic recombination. In the latter case which is of practical interest to the fusion power program an electron with the proper velocity incident on a highly charged ion is resonantly captured and simultaneously interacts with an inner shell electron to excite it, thus forming a doubly excited state which may decay predominantly by X-ray emission for higher Z ions or by Auger electron decay for lower Z ions. The resonant velocity is that of the Auger electron emitted by the ion in the doubly excited state in RTE the electrons to be captured are in low Z atomic (typically He) or Molecular (typically H2) targets and the ions are produced by accelerators in highly charged states with the appropriate resonant velocity. The resonance is much broadened by the velocity distribution of the target electrons. Thus the resonance width as a function of projectile energy is determined by folding the Compton profile of the target electrons with the dielectronic recombination cross sections. A weaker effect and more speculative is Two Electron Transfer Excitation. Here one target electron excites the projectile 1s electron to the 2p shell for example and the other target electron is captured to an excited state of the projectile. This effect becomes more important at projectile energies higher than the energy where the RTE cross section has its maximum value. The electron--electron interaction has been beautifully demonstrated by Zouros et al. Finally, there might be interference with shakeup. This paper will present angular distribution measurements of Auger lines so that the effects of interference between these various processes can be studied