SPECTRA ANALYSIS OF THE XPS CORE AND VALENCE ENERGY-LEVELS OF POLYMERS BY AN AB-INITIO MO METHOD USING SIMPLE-MODEL MOLECULES

The X-ray photoelectron spectra (XPS) of polyacrylic acid (PAA), polyvinyl acetate (PVAc), and polymethyl methacrylate (PMMA) were analyzed by an ab initio MO method using molecules of 1,3,5-hexanetricarboxylic acid (HCA), 1,3,5-triacetoxy hexane (TAH), and dimethyl 2-methylpentane 2,4-dicarboxylate (MMPC), respectively. The theoretical spectral patterns derived from the Gelius-Siegbahn model showed good agreement with the spectra observed between 0-30 eV. The present results suggest several new assignments for the XPS spectra. The valence-level O2s spectra of the polymers at around 27 eV correspond to ssigma (O2s-C2s)-bonding and psigma (O2s-C2p)-bonding orbitals arising from the -O- and O=C< groups. For PMMA, the broader core-level C1s spectra at around 285.0 eV were found to be due to four components, -O-CH3, > C <, -CH2 and -CH3, respectively.