  Fully Differential Cross Sections (FDCS) for single electron capture from
helium by heavy ion impact are calculated using a frozen core 3-Body model and
an active electron 4-Body model within the first Born approximation. FDCS are
presented for H+, He2+, Li3+, and C6+ projectiles with velocities of 100
keV/amu, 1 MeV/amu, and 10 MeV/amu. In general, the FDCS from the two models
are found to differ by about one order of magnitude with the active electron
4-Body model showing better agreement with experiment. Comparison of the models
reveals two possible sources of the magnitude difference: the inactive
electron's change of state and the projectile-target Coulomb interaction used
in the different models. Detailed analysis indicates that the uncaptured
electron's change of state can safely be neglected in the frozen core
approximation, but that care must be used in modeling the projectile-target
interaction.
