(e, 2e) spectroscopy of the CO molecule

The noncoplanar symmetric ($e, 2e$) reaction is applied to the CO molecule at 1200 and 400 eV. The valence-state structure of the ion extends from 14 to 63 eV. Momentum profiles are measured for different fixed separation energies and shown to correspond closely to the plane-wave off-shell impulse approximation for electron orbitals given by self-consistent field calculations. Much structure is observed outside the main peaks. It is shown to be due mostly to configuration interaction of the $3\sigma$ hole state with core-excited states. Qualitative features of a configuration-interaction calculation are confirmed in terms of both momentum profiles and the spectroscopic strengths of ion states. The spectroscopic sum rule is satisfied within experimental error, confirming the validity of the analysis.