THE INTERPRETATION OF X-RAY PHOTOELECTRON-SPECTRA OF PYROLIZED S-CONTAINING CARBONACEOUS MATERIALS

Theoretical models and ab initio Hartree-Fock wavefunctions have been used to investigate the S(2p) core level binding energies (BE), of pyr olized S-containing, carbonaceous materials. Comparison between experi mental and calculated data for thiophene permits the accuracy of the p resent approach to be established. A systematic study of different sit uations demonstrates that, in these materials, non-oxidized S atoms ca n show peaks at very high BE relative to the C(ls) peak at 285.0 eV. T his study confirms that the peak at 164.1 eV corresponds to 'thiopheni c' S atoms. On the other hand, it shows that the peaks at higher BE co uld correspond to S atoms replacing C atoms in three-coordinated struc tures of graphene layers, in agreement with the arguments suggested in the experimental works. The energetic similarity between the two peak s at very high BE makes it difficult to differentiate between them, al though the results of the present study seem to suggest that the peak at experimental BE approximate to 166 eV could correspond to S atoms c oordinated to two C and one H atoms at the edge of graphene layers, wh ile the peak at approximate to 169 eV would correspond to S atoms repl acing C atoms in inner positions of the graphene layers, and it is bon ded to three C atoms. (C) 1997 Elsevier Science Ltd.