Experimental evidence of transfer excitation in Ar6+-He collisions

High-resolution cold-target recoil-ion momentum spectroscopy (COLTRIMS) has been used to study single-electron capture processes in collisions of Ar 6+ ions with He at an impact energy of 9 keV and scattering angles between 0 and 3 mrad. The energy-gain spectra show that the capture occurs mainly into the 4s state with a significant contribution involving capture into the 4p state. Reaction channels associated with transfer excitation into the 3s3p3d states of Ar 5+ are also observed for the first time, accounting for 6 .0:4/% of the total cross sections for single- electron capture. Experimental results are found to be in good agreement with the two-electron atomic orbital close-coupling calculations.