Longitudinal and transverse recoil electron capture processes in 0.5-50 keV/u C5+-He collisions

A high resolution cold target recoil-ion momentum spectroscopy (COLTRIMS), capable of measuring simultaneously the longitudinal and the transverse rec oil momenta, has been used for the study of state-selective single- and dou ble-electron capture by C5+ ions from He at laboratory impact energies betw een 0.5 and 50 keV/u. The longitudinal momentum spectra for single-electron capture indicate that the dominant reaction channel observed is due to cap ture into the n = 3 state of the product C4+ ions. This reaction channel co ntributes mainly to the total cross section for single-electron capture, in agreement with the close-coupling calculations. At a collision energy of 3 5 keV/u, the spectrum for the autoionizing double-electron capture illustra tes that capture into the asymmetrical C3+(2l, n'l') states (n' = 3 to infi nity) dominates, while capture into the symmetrical C3+(2l, 2l') and C3+(3l , 3l') states show less contributions. True double-electron capture occurs predominantly into the asymmetrical C3+(2l, n'/l') states with n' = 3 to in finity.