Bond information probes

X-Ray photoelectron spectroscopy (XPS) involves core ionization which shows chemical shifts used to determine oxidation state and bonding information probes exchange interactions between metal d and core electrons which directly relate to Fermi contact contribution to hyperflne metal-ligand bonding information from satellite structure... 

Keywords Bond information probes Bond localization Chemical bonds Chemical reactivity Contra-gradience criterion Covalent/ionic bond components Direct/indirect bond multiplicities Entropic bond indices Fisher information Information theory Molecular information channels Orbital... 

EXAFS is a nondestructive, element-specific spectroscopic technique with application to all elements from lithium to uranium. It is employed as a direct probe of the atomic environment of an X-ray absorbing element and provides chemical bonding information. Although EXAFS is primarily used to determine the local structure of bulk solids (e.g., crystalline and amorphous materials), solid surfaces, and interfaces, its use is not limited to the solid state. As a structural tool, EXAFS complements the familiar X-ray diffraction technique, which is applicable only to crystalline solids. EXAFS provides an atomic-scale perspective about the X-ray absorbing element in terms of the numbers, types, and interatomic distances of neighboring atoms. 

In the FIM the ions are generated at the surface from incident neutrals. In other ion-probe methods the incident beam is already ionized and three major features may be distinguished when it interacts with a surface sputtering and desorption, ion neutralization, and ion scattering. Detection of secondary ions forms the basis of secondary-ion mass spectrometry (SIMS) which is well established as a technique for surface analysis (see ref 208 for a previous review in this series) while ion-neutralization spectroscopy (INS) yields both structural and bonding information on surface species (see ref 209). 

Polymers and biopolymers often show only small and unspecific absorption. Then the use of special chromophores offers an alternative way to get additional information. Probes for, for example, pH (indicator molecules) or polarity (e.g., pyridinium betaine dyes) might be attached by chemical bonds (label) or physical interactions on the systems under investigation. 

Figure 4 Representation of the surface of a Lee and Meisei coiioidai particie. The citrate is beiieved to be bonded to the siiver, which is present as Ag, with negativeiy charged carboxyiate groups. (Rodger C, Smith WE, Dent G, and Edmondson M (1996) Surface-enhanced resonance-Raman scattering An informative probe of surfaces. Journal of Chemical Society, Dalton Transaction 79t-799 reproduced by permission of The Royai Society of Chemistry.)...

Entropic probes of molecular electronic structure have provided attractive tools for describing the chemical bond phenomenon in information terms. It is the main purpose of this survey to summarize alternative local entropy/information probes of molecular electronic structure, explore the information origins of chemical bonds, and present recent developments in orbital communication theory (OCT) [11,12,46,54-57]. The importance of nonadditive effects in the chemical bond phenomenon will be emphasized, and the information cascade (bridge) propagation of electronic probabilities in molecular information systems, which generate indirect bond contributions due to orbital intermediaries [58-62], will be examined. 

In this chapter, three methods for measuring the frequencies of the vibrations of chemical bonds between atoms in solids are discussed. Two of them, Fourier Transform Infrared Spectroscopy, FTIR, and Raman Spectroscopy, use infrared (IR) radiation as the probe. The third, High-Resolution Electron Enetgy-Loss Spectroscopy, HREELS, uses electron impact. The fourth technique. Nuclear Magnetic Resonance, NMR, is physically unrelated to the other three, involving transitions between different spin states of the atomic nucleus instead of bond vibrational states, but is included here because it provides somewhat similar information on the local bonding arrangement around an atom. 

For thin-film samples, abrupt changes in refractive indices at interfrees give rise to several complicated multiple reflection effects. Baselines become distorted into complex, sinusoidal, fringing patterns, and the intensities of absorption bands can be distorted by multiple reflections of the probe beam. These artifacts are difficult to model realistically and at present are probably the greatest limiters for quantitative work in thin films. Note, however, that these interferences are functions of the complex refractive index, thickness, and morphology of the layers. Thus, properly analyzed, useful information beyond that of chemical bonding potentially may be extracted from the FTIR speara. 

The principles of infrared spectroscopy can be exploited to extract information on the chemical bonding of an extremely wide variety of materials. The greatest strength of the technique is as a nondestructive, bulk probe of glassy and amor-... 

Finally, a fourth motivation for exploring gas solubilities in ILs is that they can act as probes of the molecular interactions with the ILs. Information can be discerned on the importance of specific chemical interactions such as hydrogen bonding, as well as dipole-dipole, dipole-induced dipole, and dispersion forces. Of course, this information can be determined from the solubility of a series of carefully chosen liquids, as well. FLowever, gases tend to be of the smallest size, and therefore the simplest molecules with which to probe molecular interactions. 

IR spectroscopy of adsorbed carbon monoxide has been used extensively to characterize the diluted, reduced Cr/silica system [48-54,60,76,77]. CO is an excellent probe molecule for Cr(ll) sites because its interaction is normally rather strong. The interaction of CO with a transition metal ion can be separated into electrostatic, covalent a-dative, and 7r-back donation contributions. The first two cause a blue shift of the vco (with respect to that of the molecule in the gas phase, 2143 cm ), while the last causes a red shift [83-89]. From a measurement of the vco of a given Cr(II) carbonyl complex, information is thus obtained on the nature of the Cr(II)- CO bond. 

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