Electronic structure of some pyridylacetylenes studied by he I photoelectron spectroscopy: A weak orbital interaction between the nonbonding electron pair on the nitrogen atom and the in-plane π orbital in the ethynyl group

Jun Okubo, Hiraku Shinozakia, Mari Kubota, Tsunetoshi Kobayashi

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The He I photoelectron spectra (PES) of 2- and 4-ethynylpyridine were measured, and the origin of each ionization band was clarified. For instance, 4-ethynylpyridine shows five PES bands at 9.58, 9.9, 10.0, 10.75 and 11.84 eV in the lower energy region, the 9.9 eV and 10.75 eV bands in particular being assigned to the ionizations from the atn orbital of the pyridyl group and the in-plane b2π orbital of the ethynyl group, respectively. Furthermore, with the aid of first order perturbation theory, the 10.59 eV band of 2-ethynylpyridine has been ascribed to the ionization from the a2-like π orbital, and the 10.8 eV band to that from the in-plane b2-like π one. Through the process of the band assignments for the ethynylpyridines, it has been revealed that there is a weak interaction between the n orbital on the ortho-substituted nitrogen atom and the in-plane π orbital localized on the ethynyl group of 2-ethynylpyridine. The photoelectron spectra of 1,4-bis(2-pyridyl)-1,3-butadiyne and 1,4-bis(4-pyridyl)-1,3-butadiyne, whose π-electron systems are regarded electronically as double ones of the corresponding ethynylpyridines, were also measured, and we have succeeded in making band assignments of these compounds on the ground of the correlation energy diagram with the ethynylpyridines.

Original languageEnglish
Pages (from-to)267-276
Number of pages10
JournalJournal of Electron Spectroscopy and Related Phenomena
Issue number3
Publication statusPublished - 1996 Apr 30



  • Bis(pyridyl)butadiyne
  • Ethynylpyridine
  • Non-bonding electron pair
  • Photoelectron spectroscopy

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Radiation
  • Atomic and Molecular Physics, and Optics
  • Condensed Matter Physics
  • Spectroscopy
  • Physical and Theoretical Chemistry

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