Simulation of C1s Spectra of C- and O-Containing Polymers in XPS by ab initio MO Calculations Using Model Oligomers

Abstract

C1s spectra of molecules [CH2=CH(COOH), CH2=CH-COOCH3, CH2=C(CH3)COOCH3, CH3-CH(CH3)COOCH3] in gas and fifteen polymers [(CH2-CHR)n (R=H, CH3, OH, OCH3, COCH3, COOH, OCOCH3, COOCH3), ((CH)k-O)n (k=1–4), (CHR-CO-O)n (R=H, CH3), and (CH2-C(CH3)COOCH3)n] in X-ray photoelectron spectroscopy (XPS) were simulated from Koopmans’ theorem by ab initio MO calculations of HONDO7 program using the model oligomers. The calculated C1s 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 C1s energy levels of the gas molecules and the model oligomers, respectively. The difference between the shifted values (21.0 and 14.4 eV) approaches to the WD (5.2–6.4 eV) of ten 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.