Contribution of edge-carbon atoms and non-benzenoid rings in graphitic carbons to π* peak profiles in CK-XANES spectra

Abstract

In order to analyze the local structure of graphitic carbons by soft X-ray absorption spectroscopy, CK-XANES spectra of polycyclic aromatic compounds having 5-membered pentagonal or 7-membered heptagonal rings were theoretically analyzed by first-principles calculations. Pentagonal rings in the bent graphitic structure take different π* orbital states. Hence, pentagonal rings split the π* peak into two peaks in CK-XANES spectra. Heptagonal rings create electrostatic potential holes in graphitic structures, and the carbon atoms in the heptagonal ring can be regarded as conjugated edge carbon atoms. Hence, heptagonal rings also split the π* peak into two peaks. Edge-carbon atoms split the π* peak into two peaks in CK- XANES spectra. Consequently, carbon atoms in non-benzenoid rings and the edge-carbon atoms in graphitic structures make the π* peak profile wider when compared to graphite.