title: Probing weak molecular orbital interactions in non-conjugated diene molecules by means of near-edge X-ray absorption spectroscopy.
abstract: Carbon and oxygen near-edge X-ray absorption fine structure (NEXAFS) spectra of 1,4-cyclohexadiene, p-benzoquinone, norbornadiene, norbornadienone, and cis-cis-[4,4,2]propella-3,8-diene-11,12-dione were calculated by means of Hartree-Fock and hybrid density functional theory using the static-exchange (STEX) approximation. The NEXAFS spectra are used as a probe to identify weak molecular interactions between the two non-conjugated ethylenic pi* orbitals present in these molecules. We show that the X-ray absorption spectrum of 1,4-cyclohexadiene exhibits some particular spectral structures in the discrete energy region that evidence diene through-bond orbital interaction, whereas absorption peaks are identified in the norbornadiene and norbornadienone spectra that indicate effective through-space orbital interactions. The molecular structure of the cis-cis-[4,4,2]propella-3,8-diene-11,12-dione isomer is such that the indirect through-bond or through-space diene orbital interactions are too weak to be assigned by its C1s NEXAFS spectrum.
authors.affiliation: Theoretical Chemistry, Roslagstullsbacken 15, Royal Institute of Technology, S-106 91 Stockholm, Sweden. viviane@theochem.kth.se
authors.forename: V C
authors.initials: VC
authors.lastname: Felicíssimo
authors.forename: A
authors.initials: A
authors.lastname: Cesar
authors.forename: Y
authors.initials: Y
authors.lastname: Luo
authors.forename: F
authors.initials: F
authors.lastname: Gel'mukhanov
authors.forename: H
authors.initials: H
authors.lastname: Agren