An electron momentum spectroscopy study on through-space and through-bond interactions in 1,4-diazabicyclo[2.2.2]octane

Electron momentum spectroscopy is applied to study the two outermost orbitals of 1,4-diazabicyclo[2.2.2]octane. From the experimental momentum profiles, it has been unambiguously concluded that through-bond interaction dominates in this molecule and that the highest occupied molecular orbital is totally symmetric while the next highest occupied molecular orbital is anti-symmetric. The importance of diffuse functions in elucidating the electronic structure of molecules is confirmed.