The cross section for projectile impact excitation±ionization of helium is calculated, including spatial correlation, time-ordering, and interference between autoionizing and continuum states. The computational load is greatly reduced by using con®guration-interaction (CI) helium wave functions and continuum pseudostates, yielding a scattering amplitude that is a sum of analytical terms for the ®rst-order and energy-conserving second- and third-order contributions, and a one-dimensional integral for the energy-nonconserving second-order contributions. Comparison is made with experiment
