Chemical states

The various spectroscopic methods do have in common that they typically allow analysis of the surface composition. Some also allow an estimation of the chemical state of the system and even of the location of nearest neighbors. 

ESR Electron spin (paramag- Chemical shift of splitting of Chemical state of adsorbed... 

NMR Nuclear magnetic resonance [223, 224] Chemical shift of splitting of nuclear spin states in a magnetic field H [225], C [226, 227], N [228], F [229], 2 Xe [230] Other Techniques Chemical state diffusion of adsorbed species... 

MS Mossbauer Spectroscopy [233-236] Chemical shift of nuclear energy states, usually of iron Chemical state of atoms... 

The Unction of this chapter is to summarize some of the general approaches to the determination of the physical and chemical state in both of the types of adsorption systems described. 

The composition and chemical state of the surface atoms or molecules are very important, especially in the field of heterogeneous catalysis, where mixed-surface compositions are common. This aspect is discussed in more detail in Chapter XVIII (but again see Refs. 55, 56). Since transition metals are widely used in catalysis, the determination of the valence state of surface atoms is important, such as by ESCA, EXAFS, or XPS (see Chapter VIII and note Refs. 59, 60). 

Electronic spectra of surfaces can give information about what species are present and their valence states. X-ray photoelectron spectroscopy (XPS) and its variant, ESC A, are commonly used. Figure VIII-11 shows the application to an A1 surface and Fig. XVIII-6, to the more complicated case of Mo supported on TiOi [37] Fig. XVIII-7 shows the detection of photochemically produced Br atoms on Pt(lll) [38]. Other spectroscopies that bear on the chemical state of adsorbed species include (see Table VIII-1) photoelectron spectroscopy (PES) [39-41], angle resolved PES or ARPES [42], and Auger electron spectroscopy (AES) [43-47]. Spectroscopic detection of adsorbed hydrogen is difficult, and... 

Elemental and chemical-state resolution affords the possibility of detecting only a monolayer or even a fraction of a monolayer. This approach is prevalent in PD and in metiiods based on x-ray fluorescence. 

Mass spectrometric investigations of the ionosphere show an abundance of molecular ions such as NO and watercluster ions [4T ]. This is an indication of the result of ion-molecule reactions which change the chemical state of the ions in this plasma ... 

Since an analyte and interferent are usually in the same phase, a separation often can be effected by inducing a change in one of their physical or chemical states. Changes in physical state that have been exploited for the purpose of a separation include liquid-to-gas and solid-to-gas phase transitions. Changes in chemical state involve one or more chemical reactions. 

These designations are popularly used to describe the basis of the laser but are not accurate descriptions of the chemical states. 

Although isotope-dilution analysis can be very accurate, a number of precautions need to be taken. Some of these are obvious ones that any analytical procedure demands. For example, analyte preparation for both spiked and unspiked sample must be as nearly identical as possible the spike also must be intimately mixed with the sample before analysis so there is no differential effect on the subsequent isotope ration measurements. The last requirement sometimes requires special chemical treatment to ensure that the spike element and the sample element are in the same chemical state before analysis. However, once procedures have been set in place, the highly sensitive isotope-dilution analysis gives excellent precision and accuracy for the estimation of several elements at the same time or just one element. 

AT the path length, and P (A) the mass absorption coefficient at wavelength A. Between absorption edges, P (A) is proportional to Z A and is nearly independent of physical or chemical state. An absorption measurement on each side of an absorption edge is required for each element analyzed. X-ray absorption is especially useful in determining heavy elements in mixed materials of lower Z, such as lead in gasoline and uranium in aqueous solution. 

Although x-rays probe inner rather than valence electrons, in light elements the chemical state of the emitting atom may affect inner-shell energies enough to be detected at high resolution. Thus the K d lines of sulfur at 0.537 nm shift by 0.3 pm between the oxidation states and. ... 

The toxicity of arsenic ranges from very low to extremely high depending on the chemical state. Metallic arsenic and arsenious sulfide [1303-33-9] AS2S2, have low toxicity. Arsine is extremely toxic. The toxicity of other organic and inorganic arsenic compounds varies (28). 

Triboelectricity. For development to occur, the toner particles must be reproducibly charged to the correct level and polarity for the specific photoreceptor. The phenomena of triboelectricity, which involves the transfer of charge from one soHd to another, are exceedingly complex, involving the surfaces of soHds and interaction of the surfaces with each other and with the ambient (52). Consequentiy, the specific experimental observations are highly sensitive to the nature and purity of the materials, the physical and chemical state of both surfaces, and the precise details of the experiments performed. 

Nano-chai acterization of materials trace metals, point defects, chemical states, and their distribution... 

SORPTION-CATALYTIC DETERMINATION OF MICRO-AMOUNT AND CHEMICAL STATE OF PALLADIUM ON SURFACE OF CARBON ADSORBENT... 

It was found that sorbed palladium might catalyse reaction of Mn(III) reduction by Cf not only after it s removing from coal, but AC with palladium, Pd/AC, has also his own catalytic effect. On the base of dependence between characteristics of AC, chemical state of palladium on AC surface and catalytic action of Pd/AC in indicator reaction it might establish, that catalytic action concerns only to non-reduced or partly reduced palladium ions connected with chloride ions on coal surface. The presence or absence of catalytic action of Pd/AC in above-mentioned reaction may be proposed for determination of chemical state of palladium on AC surface. Catalytic effect was also used for palladium micro-amounts determination by soi ption-catalytic method. 

For DTB films obtained by CVT inhomogenous distribution of out-of-framework cations and admixture capture ai e obseiwed. The aim of the present work is to use imaging X-ray photoelectron spectroscopy (i-XPS) for chemical state mapping which enable future optimization of the CVT technology. The P, O and Hg content in the DTB may be varied during the CVT. 

The diffraction mechanisms in XPD and AED are virtually identical this section will focus on only one of these techniques, with the understanding that any conclusions drawn apply equally to both methods, except where stated otherwise. XPD will be the technique discussed, given some of the advantages it has over AED, such as reduced sample degradation for ionic and organic materials, quantification of chemical states and, for conditions usually encountered at synchrotron radiation facilities, its dependence on the polarization of the X rays. For more details on the excitation process the reader is urged to review the relevant articles in the Encyclopedia and appropriate references in Fadley. ... 

---