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Abstract:
The complete kinematics of single- and double-electron capture from neon to Ar16+ was measured with a reaction microscope at a projectile energy of 3.2 keV/u (velocity vp=0.36 a.u.). Not only the change of the electronic binding energies (the Q value) and the projectile scattering angles, but also (in the case of auto-ionization) the three-dimensional momentum vectors of the emitted electrons were determined. For single-electron capture, the Q-value spectrum shows strong population of both n=7 and 8 states on the projectile, and weak contributions to n=6 and 9 are also observed. In the case of double-electron capture, auto-ionizing double capture (ADC) dominates and the populations of (n,n′)=(5,7),(6,6),(6,7) and (6,8) are observed, while true double capture (TDC) populates the (5,7) state and asymmetric states of (5,n′) with n′>10. The experimental cross sections for Auger decay with the electron energy Ee plotted as a function of the Q value suggest the occurrence of target excitation accompanying the population of configurations (5,7) and (6,6). No essential difference is found in the differential cross sections for ADC and TDC, and the angular distributions suggest that two-step processes dominate the double capture.
