Valence XPS

Several quantum-chemical studies have been performed on Hg(CN)2 and related species, applying different approaches with consideration of relativistic effects in order to get MO schemes and energies as a basis for discussion of bonding, valence XPS,105 UPS,106 XANES and EXAFS spectra.41 The latter study also showed Hg(CN)2 to be dissolved in H20 in molecular form (/-(Hg—C) 202, r(C—N) 114 pm), and obviously not to be hydrated, a remarkable finding insofar as solvates of Hg(CN)2 with various donor molecules are well known.2 However, in contrast to Cd(CN)2 (see above), Hg(CN)2 as such does not form clathrates. 

Figure 10 Theoretical and experimental valence XPS, and XES of PES (a) valence XPS with S 1-2,3 XES (b) C Ka XES and (c) O Ka XES. Reprinted from Endo et al. [85], Figure 5, with permission from Elsevier. Copyright (2001).

FIGURE 22. Valence XPS of (a) PDMS, (b) PMPS, and (c) PDHS with the simulated spectra of the model molecule using deMon. (Reprinted from Ref. 99.)... 

To our knowledge, the first published valence XPS spectrum of a macromolecule goes back to 1972 with the work of Wood et al. (12) where an experimental spectrum of was compared to a... 

Valence XPS, m, and Solution NMR Spectral Analysis of Representative Polymers by Quantum Chemical Calculations... 

In this decade, the hardware capacity of the computer rapidly progressed with remarkable development of the software performance of the quantum chemical calculation, and we are, then, able to perform the precise calculation about the electronic state of the substances. In the present work, we, thus, intend to predict valence XPS (VXPS), IR, and NMR spectra of representative polymers (polyethylene (PE), polystyrene (PS), polymethyl methacrylate (PMMA), and polyvinyl chloride (PVC)) from the latest quantum chemical calculation using the polymer model molecules. Definitely, such spectral simulations of the polymers are performed by B3LYP/6-3lH-G(d,p) basis calculations in GAUSSIAN 09 [1], and we compare the simulated spectra with the experimental results in order to discuss the electronic states of the polymers. 

The intensity of valence XPS was estimated from the relative photoionization cross section for A1 Ka radiation using the Gelius intensity model [7]. For the relative atomic photoionization cross-section, we used the theoretical values from Yeh [8]. In the intensity calculations, we used the LCAO coefficients of eigenvectors for the ground state of the model molecules derived by using a minimal basis set. 

To simulate the valence XPS, we started with a superposition of peaks centered on each VIP. As described previously [6], each peak is represented by a Gaussian-line-shaped curve. In the case of the line width ( WH(k)), we used WH(k)=0.l0 h (proportional to the ionization energy) for valence XPS. 

We already performed the detailed analysis for valence XPS of more than 60 polymers by DFT calculations using the model molecules [14]. In this section, we aim to simulate valence XPS, IR, and solution NMR spectra of PE, PS, PMMA, and PVC polymers using the model oligomers by B3LYP/6-31+G(d, p) basis calculations and to secondly clarify the electronic states of valence XPS, IR spectra, and solution NMR chemical shifts for the polymers. 

In Fig. 21. la-d, valence photoelectron spectra refiect the differences in the chemical structures between four polymers (PE, PS, PMMA, PVC). For the valence band XPS spectra in Fig. 21.la-d, the calculated spectra correspond well to the experimental ones. It can be predicted from the present MO results that valence XPS spectra of the polymers reflect the electronic state at the ground state of each polymer due to the good accordance of simulated spectra with the experimental results. 

Fig. 21.1 Valence XPS of four polymers (upper, experimental, lower simulated) (a) PE, (b) PS, (c) PMMA, and (d) PVC...

Table 21.1 Observed peak, VIP, main AO photoionization cross-section, orbital nature, and functional group for valence XPS of PS...

We have analyzed valence XPS, IR spectra, and NMR shifts of four polymers (PE, PS, PMMA, PVC) by quantum chemical calculations (B3LYP/6-31+G(d,p) basis calculations in GAUSSIAN 09) using the model oligomers (H-(CH2-CH2)io-H, H- CH2-CH(C6H5) 3-H, H- CH2-C(CH3)C00CH3 3-H,... 

From these results, we should be able to identify new polymers in the future from the valence XPS shifts, IR spectra, and NMR shifts using quantum chemical calculations. 

In the case of valence XPS simulation, the second geometry optimization was performed with ADF program. We simulated valence XPS of four substances (Chito, DLC, AC, and GP) by using the SAOP method to obtain reliable vertical ionization potentials (VIP)s in the ADF program. The potential is a statistically weighted interpolation scheme connecting the GLLB potential [13,14] to the modified LB potential [15,16]. The potential is an excellent... 

Bureau C, Chong DP, Endo K, Delhalle J, Eecayon G, Le Moel A (1997) Recent advances in the practical and accurate calculation of core and valence XPS spectra of polymers from interpretation to simulation Nucl Instr Meth Phys Res B 131 1-12... 

Figure 15 shows theoretical and experimental results for the valence XPS and the... 

Fig. 15. Calculated and measured valence XPS and BIS spectra (Schneider et al. 1985, or references therein). To the left the assumed shape of V e) and the position of the f-level (the dashed line denoted f ) are shown. The values of Wf and A are also shown, where A is the maximum of A Gaussian...

THEORETICAL INTERPRETATION OF VALENCE XPS SPECTRA OF STEREOREGULAR ORGANIC POLYMERS... 

Such successful comparisons between theory and experiment in the case of polyethylene raised questions as to how sensitive a valence XPS spectrum could be on the structure of polymers. 

In 1975 theoretical calculations on four conformations of polyethylene, T,G, TG and TGTG revealed differences in the shape of their density of states that should be observable through XPS measurements provided these conformations could actually be isolated, which is not the case. However it was an incentive to reconsider this previous calculation on polypropylene erroneously assumed in an all-trans conformation. As a result of this simple modification in the model geometry, 2/3i-helix, the theoretical spectrum came in close agreement with experiment. This suggested also that very mild structural changes can influence the shape of the valence XPS spectra and thereby become observable. 

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