Soft X-ray absorption spectra in the CK region of carbon black and spectral analysis using the discrete variational Xα method

Abstract

To investigate the local structure of carbon black (CB) crystallites, soft X-ray absorption spectra (XAS) in the CK region of CB were measured using synchrotron radiation, and the π^* peak profile in the CK-XAS was analyzed by the discrete variational (DV) Xα method. Compared to highly oriented pyrolytic graphite (HOPG), CB exhibits a broader π^* peak profile where the intensity of the broad portion in CB is proportional to the hydrogen occluded in the CB. However, the broad portion cannot be reduced even in H₂-degassed CB by thermal desorption. These findings on the broad π^* peak profile can be simulated by the unoccupied C2p density of states (DOS) of the carbon atoms that form the nonbenzenoid rings and hydrogenated edge carbon atoms. Therefore, plausible origins for the broad π^* peak in the CK-XAS of CB are the nonbenzenoid structure and/or hydrogenated edge carbon atoms in the graphitic crystallites.