Norbornane: An investigation into its valence electronic structure using electron momentum spectroscopy, and density functional and Green’s function theories

We report on the results of an exhaustive study of the valence electronic structure of norbornane $(C7H12),$ up to binding energies of 29 eV. Experimental electron momentum spectroscopy and theoretical Green’s function and density functional theory approaches were all utilized in this investigation. A stringent comparison between the electron momentum spectroscopy and theoretical orbital momentum distributions found that, among all the tested models, the combination of the Becke-Perdew functional and a polarized valence basis set of triple-ζ quality provides the best representation of the electron momentum distributions for all of the 20 valence orbitals of norbornane. This experimentally validated quantum chemistry model was then used to extract some chemically important properties of norbornane. When these calculated properties are compared to corresponding results from other independent measurements, generally good agreement is found. Green’s function calculations with the aid of the third-order algebraic diagrammatic construction scheme indicate that the orbital picture of ionization breaks down at binding energies larger than 22.5 eV. Despite this complication, they enable insights within 0.2 eV accuracy into the available ultraviolet photoemission and newly presented $(e,2e)$ ionization spectra, except for the band associated with the $1a2−1$ one-hole state, which is probably subject to rather significant vibronic coupling effects, and a band at ∼25 eV characterized by a momentum distribution of “s-type” symmetry, which Green’s function calculations fail to reproduce. We note the vicinity of the vertical double ionization threshold at ∼26 eV.