In ion atom collisions, transfer ionization is such a process in which the ionization of the target (ejection of one or more electrons) is accompanied by the transfer of an additional electron (or several electrons), often viewed as the best candidate to study electron-electron correlation, electron-outgoing projectile interaction especially for the study of the cusp shaped electron emission for the case of outgoing projectile. In IMP study, electron emissions are studied for the case of neutral outgoing projectile via selecting double-electron capture with simultaneous single ionization process (DCI) in 30 keV/u He²⁺ -Ar atom collision.

For the present DCI reaction channel, using the traditional electron spectrometer applied with double coincidence detecting measurement, D. Fregenal et al found that there was a cusp-shaped peak DDCS of electron emitted in the forward direction results [D. Fregenal, J. Fiol, G. Bernardi, S. Suarez, P. Focke, A. D. Gonzalez, A. Muthig, T. Jalowy, K. O. Groeneveld, and H. Luna, Phys. Rev. A62, 012703 (2000)].

Using the advanced Reaction Microscope using the reaction microscope technique mounted at 320-kV high voltage platform at Institute of Modern Physics, Chinese Academy of Sciences (IMP).  And triple coincidence detection measurement, the researchers found that there is no cusp shaped peak, which is contrary to the D. Fregenal’s result. Furthermore, combined with potential curve of He^2+-Ar and final state interaction prediction based on the s-wave scattering theory, a qualitative explanation has been provided. Finally, it is concluded that the cusp shaped peak does not exist in the current reaction channel.

The results have been published in Physical Review A. 89. 032708 (2014).

Fig. Double differential cross sections of electron emission in the DCI process of 30 keV/u He²⁺ on argon collision. The red dots and the black dots represent the results of D. Fregenal et al. and our results (Image by IMP).