STATE-SELECTIVE DIFFERENTIAL CROSS-SECTIONS FOR DOUBLE-ELECTRON CAPTURE IN 0.25-0.75-MEV HE2-HE COLLISIONS()

For 0.25-0.75-MeV He2+ on He collisions we have measured total state s elective double capture cross sections and cross sections differential in projectile scattering angle. For 0.25 MeV we present also state-se lective scattering-angle-dependent double-capture cross sections. The projectile energy loss (the final electronic state) as well as the tra nsverse momentum transfer (i.e., the projectile scattering angle) have been obtained by measuring the momentum vector of the recoil ion usin g cold target recoil ion momenum spectroscopy. The resonant transfer t o the ground state is found to be by far the dominant double-capture c hannel. Capture to nonautoionizing excited states is smaller by about a factor of 7, and results in larger scattering angles than the ground -state double capture. [S1050-2947(98)06801-2].