Production of autoionizing states by double-electron capture in intermediate-energy C4++ He collisions

We have performed a kinematically complete experiment for state-selective double-electron capture occurring in 15-keV/u C4+ + He collisions by means of cold-target recoil-ion momentum spectroscopy. It was shown that capture into ground and low excited states of the C2+ ions is overwhelmingly dominant. Besides, a small fraction of autoionization decays from doubly excited states of symmetric as well as asymmetric electron configurations following endothermic double-electron capture were clearly observed. Emphasis was given to the population mechanisms of the different electron configurations. Our analysis indicates that electron-electron correlation effects may play a major role in the double-electron capture process. In addition, the large transverse recoil ion momentum of symmetric configurations as compared to asymmetric configurations for the doubly excited autoionizing states may be attributed to the different number of steps involved in the primary capture process, with the former likely produced by a two-step mechanism and the latter by a one-step mechanism.

Automated summary

We have conducted a kinematically complete experiment on state-selective double-electron capture in 15-keV/u C4+ + He collisions using cold-target recoil-ion momentum spectroscopy. Our results reveal that capture into ground and low excited states of C2+ ions is the dominant process. Additionally, we clearly observed autoionization decays from doubly excited states with both symmetric and asymmetric electron configurations after endothermic double-electron capture. Our analysis suggests that electron-electron correlation effects play a significant role in the double-electron capture process. Moreover, the larger transverse recoil ion momentum observed in symmetric configurations compared to asymmetric configurations for the doubly excited autoionizing states may be attributed to the different number of steps involved in the primary capture process, with the former likely produced by a two-step mechanism and the latter by a one-step mechanism.