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The HAM/3 method was used to provide a better assignment of the valence X-ray photoelectron spectra of 16 polymers involving nitrogen, oxygen, fluorine, a glucose unit, and a benzene nucleus using the monomer, dimer or trimer model molecules without consideration of the contraction factor of the energy scale. The calculated Al Kα photoelectron spectra were obtained using Gaussian functions of a fixed approximate linewidth, 0.10 Ik and Ik = I′k − WD, where I′k is the vertical ionization potential of each MO and WD is an approximate shift to account for the work function of the sample and other energy (polarization energy and so on) effects. We assumed that WD corresponds to the shift that we must apply before we can compare the calculated spectrum for the single model molecule with the observed spectrum for the solid. The approximate linewidth corresponds to the experimental result that the inner valence spectra are broader. The theoretical spectra showed good agreement with the spectra of the polymers observed between 0—40 eV.

ABSTRACT:Cls spectra of molecules [CH2 =CH(COOH), CH2 =CH---COOCH 3 , CH 2 =C(CH 3 )COOCH 3 , CH 3 -CH-(CH3)COOCH3] in gas and fifteen polymers . (R = H, CH3, OH, OCH 3, COCH3, COOH, OCOCH 3 , COOCH 3 ), ((CHh-O). (k = 1---4), (CHRCO-O). (R= H, CH3), and (CH 2-C(CH 3)COOCH3).] in X-ray photoelectron spectroscopy (XPS) were simulated from Koopmans' theorem by ah initio MO calculations of HONDO7 program using the model oligomers. The calculated Cls spectra were obtained using Gaussian lineshape functions of each fixed linewidth of 0.54 and 1.3 eV for the gas molecules and the oligomers, respectively. The theoretical spectra showed fairly good accordance with the experimental spectra, although the shifted values were used as 14.4 and 21.0 eV for core Cls energy levels of the gas molecules and the model oligomers, respectively. The difference between the shifted values (21.0 and 14.4eV) approaches to the WD (5.2~6.4eV) often polymers as obtained by deMon density-functional calculations using model molecules with scaled-pVTZ basis set. This is due to the relation of solid effects between the experimental core-electron binding energies of polymers and theoretical MO eigenvalues of the oligomer models, as stated in the previous work.KEY WORDS X-Ray Photoelectron Spectroscopy/ Cls Spectra/ Ab Jnitio MO/ Spectral Simulation/ Koopmans' Theorem / O-Containing Polymer/ Work Function/ We have currently reported on the simulation of Xray photoelectron spectra of polymers by MO calculations using the model molecules. 1 -10 The theorem of the MO calculations can be classified into three typical cases: (a) the Koopmans' theorem, (b) delta-SCF, and (c) Slaters' concept 11 of the transition-state. In the case (a), we offered a good analysis 2 -4 of Cls spectra with Koopmans' values for four polymers [(CH2-CHR)n (R=OH, COOH, OCOCH 3 ) and (CH 2 -C(CH 3 )COO-CH3)nJ, although the shifted value was used as 21.0 eV for core Cls energy levels of the model oligomers. The reason relies on it that the differences between core energy levels as obtained using calculations of the neutral parent molecules approximate the ones as observed for the ionized molecules in XPS, although the nuclear positive charges strongly attract the core electrons in the deep potential of the ionized state. However, in the case of valence electron spectra, the energy scale of the simulated spectra 12 -14 using the Koopmans' theorem had to be contracted and shifted for a good fit with the observed spectra. This means that the energy levels in valence electron region of a ionized molecule are narrowed more than the Koopmans' values in the range of the neutral parent molecule, since there are valence electrons in the shallow potential.The method of delta-SCF (case (b)) gave quite reliable values 15 • 16 of the core-electron binding energies (CEBEs), but suffers from occasional failures. In recent papers, 5 -10 we have performed the theoretical better assignment of valence-band spectra for 60 polymers due to Slater's idea of the transition-state (case (c)) by semiemp...