SIMULATION OF XPS OF POLY(VINYL ALCOHOL), POLY(ACRYLIC ACID), POLY(VINYL ACETATE), AND POLY(METHYL METHACRYLATE) POLYMERS BY AN AB-INITIO MO METHOD USING THE MODEL MOLECULES

The X-ray photoelectron spectra (XPS) of polymers [(CH2-CHR)(n) (R=OH, COOH, and OCOCH3) and (CH2-C(CH3)COOCH3)(n)] were simulated by an ab initio MO method using model molecules of [H-(CH2-CHR)(3)-H (R=OH, COOH, and OCOCH3) and H-(CH2-C(CH3)COOCH3)(2)-H, respectively. The calculated Al-K-alpha photoelectron spectra were obtained using Gaussian functions of a fixed linewidth of 2.1 and 1.3 eV for core O-1s and C-1s energy levels, respectively, and given using Gaussian functions of a fixed approximate linewidth (0.15E(k) for valence energy levels. E(k)=E'(k)-(E(DKT)+WD), where E'(k) is the eigenvalue of each MO and (E(DKT)+WD) is an approximate shift in the energy scale to account for sum of the difference due to the Koopmans' theorem and work function and other energy effects. We assumed that the sum corresponds to the shift we must apply before we can compare the calculated spectrum for the single model molecule with the observed spectrum for the solid. The theoretical spectra without considering the contraction factor in the energy scale showed fairly good agreement with the spectra of polymers as observed, although the shift values were used as 10, 26.5, and 21.5 eV for valence, core O-1s and C-1s core energy levels of the four polymers, respectively.