Halides, alkali

Using a surface ionization detector and a tunable dye laser, Van Veen and his colleagues (202) studied the photolysis of KI between 265 and 335 nm using the TOF technique. They were able to show from the TOF spectra that only ground state were 

FIGURE 13. The dashed curve is part of a repulsive potential curve for IC1 constructed from experimental data (201). The solid line is taken from Child and Bernstein (216). Re denotes the ground state equilibrium distance and the horizontal line is the Franck-Condon region probed in the experiment. The figure was reproduced from reference (201) with permission of Elsevier Science Publishers. 

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Rasaiah J C 1970 Equilibrium properties of ionic solutions the primitive model and its modification for aqueous solutions of the alkali halides at 25°C J. Chem. Phys. 52 704... 

Miller T M, Leopold D G, Murray K K and Lineberger W C 1986 Electron affinities of the alkali halides and the structure of their negative ions J. Chem. Phys. 85 2368-75... 

Meng J, Pandey R, Vail J M and Kunz A B 1989 Impurity potentials derived from embedded quantum olusters Ag" and Cu" transport In alkali halides J. Phys. Condens Matter 1 6049-58... 

Zuo J, Pandey R and Kunz A B 1992 Embedded-oluster study of Cu -lnduoed lattloe relaxation In alkali halides Phys. Rev. B 45 2709-11... 

Cortona P 1992 Direct determination of self-consistent total energies and charge densities of solids A study of the cohesive properties of the alkali halides Phys. Rev. B 46 2008... 

Three-body and higher terms are sometimes incorporated into solid-state potentials. The Axilrod-Teller term is the most obvious way to achieve this. For systems such as the alkali halides this makes a small contribution to the total energy. Other approaches involve the use of terms equivalent to the harmonic angle-bending terms in valence force fields these have the advantage of simplicity but, as we have already discussed, are only really appropriate for small deviations from the equilibrium bond angle. Nevertheless, it can make a significant difference to the quality of the results in some cases. 

Dick B G and A W Overhauser 1958. Theory of the Dielectric Constants of Alkali Halide Crj stals. Physical Review 112 90-103. 

Materials that contain defects and impurities can exhibit some of the most scientifically interesting and economically important phenomena known. The nature of disorder in solids is a vast subject and so our discussion will necessarily be limited. The smallest degree of disorder that can be introduced into a perfect crystal is a point defect. Three common types of point defect are vacancies, interstitials and substitutionals. Vacancies form when an atom is missing from its expected lattice site. A common example is the Schottky defect, which is typically formed when one cation and one anion are removed from fhe bulk and placed on the surface. Schottky defects are common in the alkali halides. Interstitials are due to the presence of an atom in a location that is usually unoccupied. A... 

The summation is over the different types of ion in the unit cell. The summation ca written as an analytical expression, depending upon the lattice structure (the orij Mott-Littleton paper considered the alkali halides, which form simple cubic lattices) evaluated in a manner similar to the Ewald summation this typically involves a summc over the complete lattice from which the explicit sum for the inner region is subtractec... 

The reaction of BF with alkali halides yields the respective alkali fluoroborates (34) ... 

The mobilities of ions in molten salts, as reflected in their electrical conductivities, are an order of magnitude larger than Arose in Are conesponding solids. A typical value for diffusion coefficient of cations in molten salts is about 5 X lO cm s which is about one hundred times higher Aran in the solid near the melting point. The diffusion coefficients of cation and anion appear to be about the same in Are alkali halides, wiAr the cation being about 30% higher tlrair Are anion in the carbonates and nitrates. 

The ionic bond is the most obvious sort of electrostatic attraction between positive and negative charges. It is typified by cohesion in sodium chloride. Other alkali halides (such as lithium fluoride), oxides (magnesia, alumina) and components of cement (hydrated carbonates and oxides) are wholly or partly held together by ionic bonds. 

Slides Plastic cavitation around inclusions in metals (e.g. metallographic section through neck in tensile specimen) SEM pictures of fracture surfaces in ductile metals, glass, alkali halide crystals. 

Many inorganic solids lend themselves to study by PL, to probe their intrinsic properties and to look at impurities and defects. Such materials include alkali-halides, semiconductors, crystalline ceramics, and glasses. In opaque materials PL is particularly surface sensitive, being restricted by the optical penetration depth and carrier diffusion length to a region of 0.05 to several pm beneath the surface. 

The transport of charged ions in alkali halides and, later on, in (insulating) ceramics is a distinct parepisteme, because electric fields play a key role. This large field is discussed in Schmalzried s 1995 book, already mentioned, and also in a review by one of the pioneers (Nowick 1984). This kind of study in turn led on to the developments of superionic conductors, in which ions and not electrons carry substantial currents (touched on again in Chapter 11, Section 11.3.1.1). 

A problem with studies on inert gas is that the interactions are so weak. Alkali halides are important commercial compounds because of their role in extractive metallurgy. A deal of effort has gone into corresponding calculations on alkali halides such as LiCl, with a view to understanding the structure and properties of ionic melts. Experience suggests that calculations at the Hartree-Fock level of theory are adequate, provided that a reasonable basis set is chosen. Figure 17.7 shows the variation of the anisotropy and incremental mean pair polarizability as a function of distance. 

With primary alkyl halides 1 the Finkelstein reaction proceeds by a Sn2-mechanism. An alkali halide is used to deliver the nucleophilic halide anion ... 

Alkali-gehalt, m. alkali content. gelb, n. alkali yellow. -gestein, n. alkali rock, -halogenid, n. alkali halide, alkalihaltig, a. containing alkali. 

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