$\mathrm{}(e,2e)\mathrm{}$ ionization-excitation of ${\mathrm{H}}_2$

Binary $\mathrm{}(e,2e)\mathrm{}$ measurements are reported for ionization-excitation processes of ${\mathrm{H}}_2.$ 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 $2s{\sigma }_g$ and $2p{\sigma }_u$ excited final ion states are presented as normalized intensities relative to the cross section of the primary ionization to the $1s{\sigma }_g$ 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 $\mathrm{}(e,2e)\mathrm{}$ cross sections. Furthermore, the present results suggest that $2s{\sigma }_g$ and $2p{\sigma }_u$ cross sections approach their high-energy limits in different ways.