Core line spectra

To determine the BEs (Eq. 1) of different electrons in the atom by XPS, one measures the KE of the ejected electrons, knowing the excitation energy, hv, and the work function, electronic structure of the solid, consisting of both localized core states (core line spectra) and delocalized valence states (valence band spectra) can be mapped. The information is element-specific, quantitative, and chemically sensitive. Core line spectra consist of discrete peaks representing orbital BE values, which depend on the chemical environment of a particular element, and whose intensity depends on the concentration of the element. Valence band spectra consist of electronic states associated with bonding interactions between the... 

XPS and Synchrotron XPS at the sulfur edge have been used for investigating the sulfur atoms on chalcopyrite surface. Figure 10 shows synchrotron XPS sulfur 2p core-line spectra of a pristine vacuum fractured mineral and oxidized surfaces at pH 9 and The doublet in the spectra shown in Fig. 10a is a characteristic feature for pyrite, chalcopyrite and molybdenite, and it occurs due to the spin orbit coupling on sulfur. The fit... 

Fig. 4 Survey spectrum of sputter-cleaned Hf metal containing 3% Zr impurity, with all visible core-line peaks labelled, collected using a monochromatic A1 Ka X-ray source (1486.7 eV). The stepped background hatched), found in all XPS spectra, arises from photoelectrons that lose KE by inelastic electron scattering as they travel through the surface and into vacuum...

This result is actually valid far beyond the one-electron approximation because in the presence of interaction between the core hole and the surrounding electron cloud the spectral function Ai(e-co) will describe the full core level spectrum with shifted and broadened main lines, satellite lines and continua. 

The recent experimental core level spectrum by Cavell and Allison129 in Fig. 50 is very similar to that of N2 (Fig. 45), with a weak Is 3(1 jAr) satellite with 2% relative intensity at 7.2 eV above the main line, a strong 1 s 3(1 n 2 ri) satellite with 10% relative intensity at 12.2 eV, followed by a prominent discrete and continuous satellite spectrum at higher energies. The total relaxation shift is 16 eV, the MO HF ljs level lies well above the low-lying nn satellites and the limited range of the shake-up and shake-off spectrum shown in Fig. 50 only accounts for about one third of the relaxation shift (through Eq. (22)). 

Line spectrum, p. 250 Many-electron atom, p. 261 Noble gas core, p. 274 Node, p. 255 Paramagnetic, p. 269... 

The four main spectral features of XPS are best illustrated in the Cls core-level spectrum of poly-(ethylene terephthalate) film shown in Figure 3.2 [35]. The overall spectrum (solid line) is curve-fitted (deconvoluted) with four Gaussian peak components (dashed curves). The main Cls component at the BE of 285.0 eV is assigned to the six carbon atoms of the benzene ring, the peak component at 286.8 eV to the ester carbons, and the third peak at 289.0 eV to the two carboxyl carbons. The 6 2 2 stoichiometric ratio of carbon functionality is reflected approximately by the... 

Figure 1 shows a CV of a polycrystalline monoclinic WO3 electrode in 50 mM H2SO4, at a scan rate of 1 mV/s, obtained in the electrochemical preparation stage described above. There are two reduction peaks, at - 0.10 and - 0.34 V v. saturated calomel electrode (SCE), respectively. The two peaks are characteristic of polycrystalline WO3 [30-32]. The W 4f lines and the bandgap states for different electrochemical treatments are shown in Fig. 2a,b. Depending on electrochemical treatment the W 4f core level spectrum undergoes substantial changes. For a freshly prepared electrode, the spin-orbit split W 4fs/2, W 4f7/2 doublet of WO3 completely dominates... 

BE of 852.2 eV, spectrum not shown), except the core line was shifted 1 eV lower, to 851.2 eV. The negative BE shift, noted for Ni metal, may be a consequence of a strong interaction between metal clusters and the insulating support (26). Upon exposure to air (Figure 3C), peaks appeared at 853.8,855.3,and 860.9eV. These three lines match that of the NiO standard. After reoxidation at 600 C, the line for Ni° disappeared, and the remaining core envelope resembled a combination of Ni " and "Ni " states. 

X-ray photoelectron spectroscopic measurements of emeraldine base sul-fonated polyaniline (50 %) in comparison with chemically synthesized polyaniline base and its chloride salt. For polyaniline base a nearly symmetric N Is line centered close to 398.6 eV is observed, as expected from the idealized structure of the emeraldine base backbone. The deconvolution of the N Is core level spectrum shows two peaks with equal intensity, one centered at 398.9 eV due to amine nitrogen, the other located at 397.5 eV due to imine nitrogen atom. Both have an FWHM (full width at half maximum) of 1.6 eV. Similar results were obtained... 

The analysis of these materials by XPS included the use of valence band spectra. The use of valence band spectra has become more popular due to the ability to fingerprint polymer structure [21,34,35]. Spectra taken with monochromatic source XPS instruments allow analysis of the photoelectron emission from the molecular orbitals. The valence electrons are involved only in chemical bonding and not core level ionization. They give rise to valence band spectra (0-50 eV). This type of spectrum is more sensitive to changes in molecular structure than the core lines because it reflects only changes in the valence electron distribution. The valence band spectrum can act as the fingerprint of a particular valence electron arrangement in a polymer surface. The valence band spectra for the dry plasma-... 

Bonding electrons are also photoemitted and these appear in the valence band between, say 0-30 eV BE. Emission from many closely spaced levels with different cross-sections gives rise to a complex spectrum, often rich in structure, which in principle contains more direct structural information than the core level peaks. The spectrum is rather low in intensity (typically only a few percent that of major core lines) but with higher power instruments it is routinely accessible. The fingerprint utility of the valence band is increasingly being augmented by full interpretations based on theoretical calculations. 

Fig. 8. A 3d core level spectrum of CeOj showing the three different final states for each of the 3d lines. As in the case of CcjOj the 4f > and 4F> final states are strongly mixed (Allen 1985a).

The unoccupied states in the lanthanides can be reached by transitions from deep or shallow core levels. Following Wendin (1983), deep core levels are states in completely filled main shells, i.e. in the K, L and M levels. Levels in the incompletely filled main shells (N, O) are labelled as shallow core levels (except 5d, which is a valence electron level). The impact of this classification becomes clear by inspection of the strongly different types of absorption spectra, observed upon excitation of M and N core levels (fig. 6c). N,y yand M,y y spectra turn out to be completely different, although the d electrons from the shallow Nw.v levels (4d nf,n >4) reach 4f states as the photoelectrons from deep core Miy y levels (3d - nf,n > 4). Each of the M y y spectra exhibits a set of discrete narrow lines. The N,y y spectra on the other hand are dominated by a broad giant resonance above threshold (cf the strong line in fig. 6c). It exhibits only a weak and extended discrete line spectrum at threshold. 

It is useful to treat the atomic absorption below the ionization (discrete line spectrum) and the continuum absorption above the ionization threshold separately. The arctan expression in eq. (1), experimentally confirmed through the K spectra, is a good approximation for the continuum absorption. The atomic absorption lines may be interpreted through optical multiplets using the Z + 1 approximation. The validity of this approximation has been successfully demonstrated in numerous cases of K and L spectra, first by Parrat (1939) in the K absorption of gaseous Ar. Here the optically determined wp Rydberg series ( > 4) of K (Z = 19 Z + 1 ) nicely fits the atomic absorption lines of 2s - 4p (K) X-ray excitation of Ar ( Z ). The Z -I-1 potential accounts for the creation of the deep core hole. The inflection point of the arctan shaped continuum absorption is located at the series limit, i.e. the first ionization potential. 

As a recent example, where the surface and bulk core lines can be completely resolved we show in Fig.7 the As3d electron spectrum from UAs(lOO) excited by synchrotron radiation at hv=80 eV. The two spin doublets, each with a spin-orbit splitting of 0.66 eV, are shifted from each other by 0,3 eV. By exposing the surface to 0.5 L O2 one can observe that only the Surface doublet is affected. In most cases the bulk-surface shift is smaller and requires both high resolving power and a careful line profile investigation to enable one to extract the above surface information. A comprehensive study of these problems with recommended procedures have been published recently by Citrin, Wertheim and Baer . ... 

Figure Bl.4.3. (a) A schematic illustration of the THz emission spectrum of a dense molecular cloud core at 30 K and the atmospheric transmission from ground and airborne altitudes (adapted, with pennission, from [17]). (b) The results of 345 GHz molecular line surveys of tlu-ee cores in the W3 molecular cloud the graphics at left depict tire evolutionary state of the dense cores inferred from the molecular line data [21],...

The evolution of the XPS C(ls), S(2p), and Al(2p) core level lines, upon A1 deposition onto poly(3-octylthiophene) films (P30T), is shown in Figure 5-15 [84. The S(2p) spectrum for the pristine polymer consists of two components, S(2p 1/2) and S(2p.v2), due to spin-orbit coupling. 

Figure 8. TEM and optical absorption of the sample implanted with 5 x 10 Au /cm (a) TEM cross-sectional micrograph (dashed lines represent the free surface and film-substrate interface) (b) nanoparticles size distribution (c) simulated optical spectra (1) Au cluster in a non-absorbing medium with n = 1.6 (2) Au cluster in polyimide (absorbing) (3) Au(core)-C(shell) cluster in a nonabsorbing medium with n = 1.6 (4) the experimental spectrum of Au-implanted polyimide sample, (d) X-ray diffraction patterns as a function of the implantation fiuence.

However, it was pointed out that two other observations are out of line with the iron(I) formulation and more consistent with an iron(II)-porphyrin radical anion [290] (1) the low-intensity red-shifted Soret band in the UV-VIS spectrum with broad maxima in the a,(3-region compared to, for instance, Fe(TPP) in THF, is typical of a porphyrin radical, and (2) the bond lengths of the porphyrin core indicate population of the (antibonding) LUMO of the ligand (i.e., the presence of an extra electron in the re-system). The presence of porphyrin radical character in the electronic ground state was also inferred from the paramagnetic NMR-shifts of the pyrrole protons at the meso and p-carbon atoms [291]. 

FIGURE 2.1 Energy of the 0-0 vibrational transition in the principal electronic absorption spectrum of violaxanthin (l Ag-—>1 BU+), recorded in different organic solvents, versus the polarizability term, dependent on the refraction index of the solvent (n). The dashed line corresponds to the position of the absorption band for violaxanthin embedded into the liposomes formed with DMPC (Gruszecki and Sielewiesiuk, 1990) and the arrow corresponds to the polarizability term of the hydrophobic core of the membrane (n = 1.44). 

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