Electron momentum spectroscopy of H-2 and D-2: Ionization to ground and excited final states

The symmetric noncoplanar (e,2e) cross sections (momentum profiles) of H-2 and D-2 for the transitions to the 2p sigma(u) and 2s sigma(g) excited ion states have been measured, relative to the ground-state ion transition, using a high-sensitivity multichannel momentum-dispersive electron momentum spectrometer (EMS) at an impact energy of 1200 eV. Newly calculated plane-wave impulse approximation (PWIA) cross sections, based on a full-configuration-interaction H-2 wave function, are compared to the experimental results. These calculations are in better agreement with the experimental results for the transition to the 2s sigma(g) ion state than the earlier theoretical work of Liu and Smith, Jr. {[}Phys. Rev. A 31, 3003 (1985)] which has been found to be in error. Nevertheless, significant discrepancies between the relative experimental and theoretical cross sections are observed for the transitions to excited ion states, suggesting a failure of the PWIA description of these processes. The results an supported by additional measurements obtained using an energy-dispersive EMS spectrometer.