Binding Energy BE

The next property is referred to as binding energy (BE) and is defined for particle i for the configuration as follows  

Note that /ir , as defined in (5.12), coincides with the definition of the average CN given in Eq. (2,76), provided that we choose Rc of this section to coincide with Rm of Chapter 2. 

This is the work required to bring a particle from infinite distance, with respect to the other particles, to the position R. For a system of pairwise additive potentials, (5.16) reduces to 

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The films were characterized using x-ray powder diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The photoelectron spectroscopy utilized a Vacuum Generators ESCA Lab II system with Mg(Ka) radiation. Binding energies (BE) were measured with respect to the surface C(ls) peak (284.5 eV) which was always present In these films. Scanning electron microscopy was done with a JEOL JSM-35C system. 

The XPS spectra of the freshly sulfided Co-Mo/NaY catalysts were measured on an XPS-7000 photoelectron spectrometer (Rigaku, A1 anode 1486.6 eV). The sample mounted on a holder was transferred from a glove bag into a pretreatment chamber attached to the spectrometer as possible as carefully not to be contacted with air. The binding energies (BE) were referenced to the Si2p band at 103.0 eV for the NaY zeolite, which had teen determined by the Cls reference level at 285.0 eV due to adventitious carbon. 

As it can be observed in Table 13.1, Ir supported over pure oxides exhibited low acidity, but Ir supported on mixed Nb20s-Si02 displayed an important enhancement in the surface acidity with surface coverage by niobia increases. Binding energies (BE) of core-level electrons and metal surface composition were obtained from XP spectra. The BE values of Si 2p, Ti 2p3/2, Nb 3ds/2 were 103.4, 458.5 and 123 eV respectively, which are exactly the expected values considering the presence of oxides of Si (IV), Ti (IV) and Nb (V). With regard to Ir 4f7/2 core level, a... 

Measurement of the kinetic energy (KE) of the outgoing electron gives experimental information on its binding energy (BE) in the molecule M. 

The 5950A ESCA spectrometer is interfaced to a desktop computer for data collection and analysis. Six hundred watt monochromatic A1 Ka X-rays are used to excite the photoelectrons and an electron gun set at 2 eV and 0.3 mAmp is used to reduce sample charging. Peak areas are numerically integrated and then divided by the theoretical photoionization cross-sections (11) to obtain relative atomic compositions. For the supported catalyst samples, all binding energies (BE) are referenced to the A1 2p peak at 75.0 eV, the Si 2p peak at 103.0 eV, or the Ti 2p3/2 peak at 458.5 eV. 

Measuring physical-chemical properties of the clusters, such as ionization potential (IP), binding energy (BE), electron (EA) and proton affinity (PA), fragmentation channels, electronic structure and so on, provides a basis for the comprehension of the intrinsic forces acting in the clusters and governing their dynamics. Theoretical computation of these quantities may provide a feedback to evaluate the quality of the calculations and the accuracy of the experimental determinations. 

The XPS mechanism, which can be used for quantitative and qualitative chemical analysis of surfaces, is based on the photoelectric effect. A monochromatic soft Mg or Al anode X-ray source is used to irradiate the surface. The absorbed X-rays ionize die core shell, and in response, the atom creates a photoelectron that is transported to the surface and escapes. The ionization potential of a photoelectron that must be overcome to escape into vacuum is the binding energy (BE) plus the work function of the material. The emitted photoelectrons have a remaining kinetic energy (KE), which is measured by using an electron analyzer. Individual elements can be identified on the basis of their BE. The resulting XP spectrum is a characteristic set of peaks for a specific element, with BE as the abscissa and counts per unit time as... 

C Is XPS spectra for the treated surfaces are not well resolved. From the deconvoluted spectra, the decreases in the main contamination peak at 284.8 eV, and the other two peaks at 1.7 and 4.0 eV higher binding energy (BE) can be followed. The intensities of these peaks are notably much lower in the oxide samples as compared with those of Y58 wafers, consistent with the lower density of surface silanols or contamination adsorption sites between the two surfaces. After vapor-phase HMDS treatment, the contribution of these peaks is greatly reduced and a new main C Is peak centered at 284.6 eV appears, as for the Y58 samples, which is assigned to the —CH3 group, due to the HMDS stabilization reaction. 

A primitive approach to molecular speciation involves identification of the molecular functionalities through the binding energies (BE s) of their constituent elements. This approach has been used to identify electropolymerized poly-pyrrole (9) and N-(0-hydroxybenzyl)anillne/tyrosine (84) films. In the latter case the identification was confirmed with multi-reflection IR spectroscopy. Both examples used either monomers or model compounds as references to generate known comparison spectra. The BE s and peak shapes have also been used to identify the presence of the ferricinium ion on freshly prepared surfaces (85). In this way the identification is similar to fingerprinting. 

The nucleus of X consists of Z protons and A — Z neutrons. Then its binding energy, BE, is given by... 

Fig. 2. Binding energy (BE) of the Au(4f 1) level in compounds of different oxydation numbers (ON), from ESCA measurements (55, 89). (For compounds 3 and 4, see Section IV,5).

The lower panel of Fig. 4 reproduces angle-resolved photoemission spectra [43] showing the dispersion of the state, i.e. how its BE changes with the angle of emission with respect to the normal. The dotted line in Fig. 3 shows schematically the E(k ) upwards parabolic dispersion of the surface state. The Binding Energy (BE) of the Cu(lll) surface state at the center of the 2D Brillouin Zone (BZ) is —400 meV relative to the Fermi energy. The effective mass for the electrons in this state is obtained from the curvature... 

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