Alkali + halogen systems

The high selectivity of RLH-catalysts to olefins is a result of a definite combination of surface oxygen state, oxygen / metal cations ratio, redox properties of metal cations and acidity-basicity balance. Further studies are needed in order to understand the role of the support and the proper functioning of RE-Alkali-Halogen systems in oxidation of low paraffins. 

At the origin of modem reaction dynamics are the scattering experiments on alkali-halogen systems which Herschbach and his school pioneered. Very rich chemical branching was observed in reactions of alkali dimer molecules with halogens [1,2], e.g. 

These reactions are certairily, like the triatomic alkali-halogen systems (e.g, K + Br2), initiated by an electron jump ( harpooning ) ... 

The harpoon model has been used on a large variety of systems, far beyond the alkali metal-halogen systems for which it was proposed originally. It is therefore necessary to describe the model on a more general basis by considering the reaction... 

Hashimoto and Grossman (1987) and Keller and Buseck (1991), for example, have argued that these phases formed by reaction of individual CAIs with a nebular gas, that also caused iron-alkali-halogen metasomatism (see below). The heterogeneous distribution of alteration phases can then be attributed to the fact that some CAIs interacted with the gas, but others did not. The interrelationship between aqueous alteration of the CV chondrites and metasomatism/oxidation will be discussed in detail below. The variable bulk compositions of the oxidized CV chondrites may be the result of nebular aqueous alteration, but could also be the result of open-system parent-body alteration as well. 

Of the systems treated in this paper, potential energy surfaces of only the simplest alkali-halogen molecule combination Li + F2 have been calculated with a corrected ab initio method yielding a wealth of information which will be discussed later in connection with the experimental information concerning related systems (Balint-Kurti, 1973, and this volume,... 

The alkali-oxygen molecule system is the most thoroughly investigated non-halogen system. Nevertheless large experimental discrepancies still exist and the interpretation is often ambiguous. Moutinho et al. (1970) report total ionization cross sections (Fig. 26) of about 5 A2 at 10 eV, but... 

Platinum is a beautiful silvery-white metal, when pure, and is malleable and ductile. It has a coefficient of expansion almost equal to that of soda-lime-silica glass, and is therefore used to make sealed electrodes in glass systems. The metal does not oxidize in air at any temperature, but is corroded by halogens, cyanides, sulfur, and caustic alkalis. 

Some of the investigations carried out in the first half of the twentieth century were related to CL associated with thermal decomposition of aromatic cyclic peroxides [75, 76] and the extremely low-level ultraviolet emission produced in different reaction systems such as neutralization and redox reactions involving oxidants (permanganate, halogens, and chromic acid in combination with oxalates, glucose, or bisulfite) [77], In this period some papers appeared in which the bright luminescence emitted when alkali metals were exposed to oxygen was reported. The phenomenon was described for derivatives of zinc [78], boron [79], and sodium, potassium, and aluminum [80]. 

Pascal s work (11—13)) electron cloud radii also seem to be transferable. We begin therefore by comparing directly the structural distances D and the diamagnetic susceptibihties xm (the direct data of experiment) for the inert gases, their isoelectronic alkali halides, and their (almost) iso-electronic halogen molecules — three systems of very different bond-types. 

In general, the salts, esters, and halogen derivatives of nitric acid represent a poor compromise between performance and stability, and their future use in liquid systems appears limited. Several salts or esters of nitric acid have, however, achieved some prominence as oxidizers or monopropellants. The most important are the nitrates of alkali metals,... 

Several theories have been proposed to explain the mechanisms involved in an AFID system (31). In general, thermal energy is required to atomize a particular alkali metal salt. The alkali metal atoms formed ionize and are subjected to an electric field. This produces a current proportional to the number of ions. The presence of halogen, phosphorus, and even nitrogen enhance the signal. The system is complex and does not lend itself to a complete theory as intricate surface phenomena are possible. In addition, there is speculation that photochemical processes occur and realization that combustion products formed in the flame can interact to form a multitude of species compound the difficulty. It has been proven that the process does depend on thermal energy and not strictly speaking on the products of combustion. For this reason many researchers prefer the term thermionic ionization. 

The (3-diketonate chelate complexes are very stable and exhibit properties which are rather typical of aromatic systems. Many of their reactions such as halogenation, alkylation and acylation can be compared with those of the P-diketonate anions associated with alkali metal cations. However, complexes of transition and other metals add to the stability of the system, so that quite vigorous reaction conditions can be employed. In most of the work carried out on P-diketonate chelates, the modified ligand has not been removed from the metal ion, but this can usually be effected if desired. 

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