A comparative study of interference effects in (e, 2e) electron momentum profiles of CO₂, ethylene and 1,3-butadiene

We report a comparative (e, 2e) study of intereference effects in the spherically-averaged electron momentum density distributions of the outermost orbitals of CO₂, ethylene and 1,3-butadiene. The experiments on the three molecular orbitals, being each composed of 2p atomic orbitals, were performed in the symmetric noncoplanar geometry and at an incident electron energy of 1.2 keV. Interference patterns have then been obtained for each molecular orbital by dividing the experimental data by (e, 2e) cross section of a 2p atomic orbital calculated by using distorted wave impulse approximation. It is clearly demonstrated that interference patterns tell about constructive or destructive nature of the overlap between the constituent 2p atomic orbitals. Furthermore, it is shown that higher instrumental momentum resolution would be required for detailed studies on interference effects in cases when two of the constituent atomic orbitals with larger spatial separation are both oriented perpendicular to the molecular axis or plane.