[Formula Presented] ionization-excitation of [Formula Presented]

Binary [Formula Presented] measurements are reported for ionization-excitation processes of [Formula Presented] The experiments were performed at impact energies of 1200, 1600, and 2000 eV using an energy- and momentum-dispersive spectrometer. Momentum profiles for transitions to the [Formula Presented] and [Formula Presented] excited final ion states are presented as normalized intensities relative to the cross section of the primary ionization to the [Formula Presented] ground ion state. The results are compared with theoretical calculations of Lermer et al. [Phys. Rev. A 56, 1393 (1997)] using the first-order plane-wave impulse approximation. Certain features of the discrepancies between experiment and theory can be explained by incorporating contributions from the second-order two-step mechanisms into the [Formula Presented] cross sections. Furthermore, the present results suggest that [Formula Presented] and [Formula Presented] cross sections approach their high-energy limits in different ways.