(e,2e) ionization-excitation of H₂

Binary (e,2e) measurements are reported for ionization-excitation processes of H₂. 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 2sσ_g and 2pσ_u excited final ion states are presented as normalized intensities relative to the cross section of the primary ionization to the 1sσ_g 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 (e,2e) cross sections. Furthermore, the present results suggest that 2sσ_g and 2pσ_u cross sections approach their high-energy limits in different ways.