2-ELECTRON CAPTURE BY C3- COMPETITION BETWEEN SINGLE AND DOUBLE-ELECTRON PROCESSES( IONS )

State-selective translational energy spectroscopy has been used to stu dy two-electron capture processes for 6 keV C3+ ions in collision with He, Ne and Ar atoms. The spectrum for the formation of C+ from the He target reveals only features resulting from double-collision single-e lectron capture processes while the spectrum for C+ from the Ne target reveals both single-collision double-electron capture and double-coll ision successive single-electron capture processes. The spectrum for t he Ar target consists entirely of double-electron capture channels in which the target product Ar2+ ion is left in the ground state with som e indication of double capture into autoionizing states of the C+ ion.