CARBON AROMATICITY BASED ON XPS-II TO XPS-II-ASTERISK SIGNAL INTENSITY

The X-ray photoelectron spectroscopy (XPS) C(1s) spectra from heavy petroleum samples and model compounds were collected and the general intensity variation of electron emission in the energy region anticipated for II to II* shake-up peaks was recorded. The XPS results were compared with the carbon aromaticity data obtained on the same samples using solution-state 13C NMR spectroscopy. For model compounds, the aromaticity was based on the known structure. A linear relationship was found between the relative XPS intensity in the II to II* region and the carbon aromaticity. Using this calibration the XPS-derived values of carbon aromaticity for Argonne premium coals were determined and compared to recent literature results from solid-state 13C NMR spectroscopy. The advantages and limitations of the XPS approach for estimation of carbon aromaticity are discussed.