Electronic spectroscopy compounds

X-ray photoelectron spectroscopy (XPS), also called electron spectroscopy for chemical analysis (ESCA), is described in section Bl.25,2.1. The most connnonly employed x-rays are the Mg Ka (1253.6 eV) and the A1 Ka (1486.6 eV) lines, which are produced from a standard x-ray tube. Peaks are seen in XPS spectra that correspond to the bound core-level electrons in the material. The intensity of each peak is proportional to the abundance of the emitting atoms in the near-surface region, while the precise binding energy of each peak depends on the chemical oxidation state and local enviromnent of the emitting atoms. The Perkin-Elmer XPS handbook contains sample spectra of each element and bindmg energies for certain compounds [58]. 

Time-of-flight mass spectrometers have been used as detectors in a wider variety of experiments tlian any other mass spectrometer. This is especially true of spectroscopic applications, many of which are discussed in this encyclopedia. Unlike the other instruments described in this chapter, the TOP mass spectrometer is usually used for one purpose, to acquire the mass spectrum of a compound. They caimot generally be used for the kinds of ion-molecule chemistry discussed in this chapter, or structural characterization experiments such as collision-induced dissociation. Plowever, they are easily used as detectors for spectroscopic applications such as multi-photoionization (for the spectroscopy of molecular excited states) [38], zero kinetic energy electron spectroscopy [39] (ZEKE, for the precise measurement of ionization energies) and comcidence measurements (such as photoelectron-photoion coincidence spectroscopy [40] for the measurement of ion fragmentation breakdown diagrams). 

Lithium foil is commercially available. Its surface is covered with a "native film" consisting of various lithium compounds [Li0H,Li20,Li3N, (Li20-C02) adduct, or Li2C03], These compounds are produced by the reaction of lithium with 02, H20, C02, or N2. These compounds can be detected by electron spectroscopy for chemical analysis (ESCA) [2], As mentioned below, the surface film is closely related to the cycling efficiency. 

A number of radical anions of sulfur-containing aromatic compounds have been studied essentially by means of ESR spectroscopy and sometimes by electronic spectroscopy. The studied compounds include aromatic rings separated by the oxidized sulfur functionality. The effects caused by the latter depend on the geometry and topology of the aromatic systems as well as on the electron-withdrawing ability of the other substituents. 

Unpaired electrons and magnetism - One of the consequences of the open (incompletely filled) d" configuration of transition-metal ions may be the presence of one or more unpaired electrons. Such compounds could be described as radicals, and they are detected by techniques such as electron spin resonance spectroscopy. 

Solomon, E. I., and Lever, A. B. P., Eds. (2006). Inorganic Electronic Spectroscopy and Structure, Vols. I and II. Wiley New York. Perhaps the ultimate resource on spectroscopy of coordination compounds. Two volumes total 1424 pages on the subject. 

These experiments also show the value of NEXAFS as a technique for following the kinetics of surface processes. We have shown that experiments can be tailored so a specific reaction can be studied, even if gas evolution is not involved. This represents an advantage over thermal desorption experiments, where several steps may be required in order to desorb the products to be detected. Another advantage of NEXAFS is that rates are measured isothermally, so the kinetic parameters can be determined with accuracy. Finally, NEXAFS is not a destructive technique, so we need not to worry about modifying the surface compounds while probing the system, as would be the case with other techniques such as Auger electron spectroscopy. 

Electronic spectroscopy has been employed to study substitution reactions of sulfoxide complexes. An interesting example (104) is the reaction of [Fe(0-Me2S0) P+ with chloride ion. Addition of one equivalent of chloride ion to a Me2SO solution of [Fe(0-Me2S0)6P+ causes a change in spectrum, but further additions have no effect. Comparisons with known compounds indicate that [Fe(0-Me2S0)5Cip+ is the major species in solution. 

In ultraviolet and visible region, electronic transition of atoms and molecules are observed. This is why it is called electronic spectroscopy. In infrared region the absorption of radiation by an organic compound causes molecular vibrations and so it is called vibrational spectroscopy. 

Chalcogenation of a divalent germanium compound with styrene sulfide has been examined as an alternative route to the first free germanethione Tbt(Tip)Ge = S 165142 (Scheme 32) and later on allowed the synthesis of new base-stabilized germanethiones 187 and 188156 [Eq. (37)]. Phenyl isocyanate also may serve as a sulfur source leading to 165, which was evidenced by electronic spectroscopy and underwent a subsequent [2 + 2] cycloaddition with phenyl isocyanate157 (Scheme 36). 

Surface Chemical Analysis. Electron spectroscopy of chemical analysis (ESCA) has been the most useful technique for the identification of chemical compounds present on the surface of a composite sample of atmospheric particles. The most prominent examples Include the determination of the surface chemical states of S and N in aerosols, and the investigation of the catalytic role of soot in heterogeneous reactions involving gaseous SO2, NO, or NH3 (15, 39-41). It is apparent from these and other studies that most aerosol sulfur is in the form of sulfate, while most nitrogen is present as the ammonium ion. A substantial quantity of amine nitrogen also has been observed using ESCA (15, 39, 41). 

The performance of the V-Mg oxide catalyst was found to depend on its composition and the method of preparation. As to the composition, it was found that catalysts containing very small or very large amounts of vanadium were not selective. The better catalysts in terms of both activity and selectivity consisted of from about 10 to 60 wt% V2O5 (35). Analyses of these catalysts by X-ray diffraction, Auger electron spectroscopy, and infrared spectroscopy showed that they contained only two identifiable phases Mg orthovanadate (Mg3(V04)2) and MgO. Since MgO had low activity and poor selectivity under the reaction conditions employed, it was concluded that the active phase was Mg orthovanadate (Mg3(V04)2). Indeed, it was later shown that this compound was a selective catalyst (26). 

The behavior toward Lewis bases was studied. The compound [R2A10CR NPh]2 did not form a stable complex with Lewis bases such as pyridine, tetrahydrofuran and triethylamine, as evidenced by IR spectroscopy, but did form with a strong bases such as trimethyl-amine oxide, Me3NO and hexamethylphosphoramide (Me2N)3PO. This fact means that the Lewis acidity of this organoaluminum is rather weak, because A1R3 forms the stable complex with a relatively weak electron donor compound such as diethyl ether and tetrahydrofuran, and R2A1NR2 with an electron donor such as triethylamine. 

The energy of a single photon is obviously insufficient to ionize an organic compound. As early as the nineteen forties (3, 4), however, it -was observed that Wurster blue cation radical is produced by photoirradiation of 3-methylpentane glass containing N,N-tetramethyl p-phenylenediamine (TMPD) at 77° K. The recent detailed study of this system by electric conductivity measurement (5, 6) and electronic spectroscopy (7) provided conclusive evidence that the ionization is brought about via excitation to the triplet state followed by successive photoabsorption at the triplet state. This mechanism is supported by the facts that the life-time of the photochemical intermediate is identical with that of phosphorescence and the formation of Wurster blue, and that phosphorescence is inhibited in the presence of triplet scavengers. 

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