Diatomic halides

Diatomic halides, uses for, 77 337 Diatomite, asbestos substitute, 3 314t Diazahemicyanine dyes, 9 257 Diazene reductions, 73 570 Diazepam, chloroacetyl chloride in production of, 7 142 Diazinon... 

Table 14. Unpaired electron distributions in diatomic halide radical anions. Sa, Pa indicate the spin population of the valence s and p orbitals of atom A, derived from the isotropic and anisotropic hyperfine coupling constants 67)...

The diatomic halides and oxides of the alkali and alkaline earth groups must, by definition, have a considerable ionic contribution to their bonding. These diatomics, together with those of Al, Ga and In, are in fact found to lie outside the predicted field for covalent bonds, as shown in Figure 5.6(d). Molecules with dative bonds are expected along the borderline between covalent and ionic types, including several fluorides (of Sb, Si, Sn, Pb, Be and Ag) and chlorides (Si, Sn). They are arbitrarily grouped with the more ionic bonds. 

This last and concluding remark is illustrated by the data for the diatomic halides in Fig. 2. Provided that it is not pushed too far and that time is not wasted in useless polemic, the Townes and Dailey method can be made to yield reliable information of value to the chemist along the lines which have been sketched above, and of which many examples are given in this monograph. 

Diatomic halides were first studied as HX by Lempka, Passmore and Price (211) showing slightly higher I than Eq. (24). It is possible by high-temperature equipment (212—214) to study diatomic alkaline halide molecules (or ion-pairs)... 

Examination of the electronic configurations and levels for diatomic halides having 12 valence electrons, such as PF (3) PCI (6), NCI, and NF (7) suggests that the ground state for SCl" is most likely e, and several low-lying excited states are expected. 

Table 24 Dissociation energies and absorption wavelengths for diatomic halides (MX) of the Group 13 elements. (Source K. Dittrich and B. Vorberg, Chemia Analityczna (Warsaw), 1983, 28, 539)...

An Xc2 excimer laser has been made to operate in this way, but of much greater importance are the noble gas halide lasers. These halides also have repulsive ground states and bound excited states they are examples of exciplexes. An exciplex is a complex consisting, in a diatomic molecule, of two different atoms, which is stable in an excited electronic state but dissociates readily in the ground state. In spite of this clear distinction between an excimer and an exciplex it is now common for all such lasers to be called excimer lasers. 

The lower halides of Bi are rather different. The diatomic species BiX (X = Cl, Br, I) occur in the equilibrium vapour above heated Bi-BiX3 mixtures. A black crystalline lower chloride of composition BiCli.iev is obtained by heating Bi-BiCls mixtures to 325° and cooling them during 1-2 weeks to 270° before removing excess BiC by sublimation or extraction into... 

The 4-4 oxidation state, which for Nb and Ta is best represented by their halides, is most notable for the uniquely stable VO + (vanadyl) ion which retains its identity throughout a wide variety of reactions and forms many complexes. Indeed it is probably the most stable diatomic ion known. The M ions have only slightly smaller radii... 

Oxidative UPD involves the oxidation of species to form an atomic layer where the precursor contains the element in a negative oxidation state. A classic example is the formation of oxide layers on Pt and Au, where water is oxidized to form atomic layers of oxygen. Halide adsorption can be thought of similarly, where a species such as I oxidatively adsorbs on a metal surface as the halide atom. In that case, a bulk film is not formed at more positive potentials, but the diatomic is generated and diffuses into solution. With respect to compound formation, oxidative UPD from a sulfide solution is a good example ... 

The validity of the method was rechecked with data from Herzberg s recent compilation on gaseous diatomics (121) (Table XI). Calculated heats of solid halides are in better agreement with experimental values. In some molecules the use of more than one value of fluorine bond energy is required to reproduce experimental heats. Thus PFS or AsFs require two fully weakened values and three unweakened values, which is sensible on chemical and structural grounds. 

More recently, a novel type of halogenating enzyme, named hydroperoxide halolyase, which generates halogenated aldehydes, has been described in the marine diatom Stephanopyxis turris (Wichard and Pohnert 2006). In other microalgae, halogenation of organic compounds was shown to mainly involve methyl halide transferases (Moore et al. 1996 Manley 2002), and no vHPO has yet been identified on genomic data obtained from diatoms (Scala et al. 2002 Armbrust et al. 2004). Clearly, these emissions are not directly associated with an oxidative burst. 

In this type of Laser, the active medium consists of an inert gas (X) or of a mixture of an inert gas and a halide gas (X + Y). The term excimer stands for excited dimmer which refers to a diatomic molecule of two inert gas atoms (XX) or a molecule of an inert gas atom and a halide gas atom (XY). ... 

Other enzymes capable of halogenation processes include a bacterial esterase from Pseudomonas fluorescens (2316), acid phosphatases from the bacteria Shigella flexneri and Salmonella enterica ser. typhimurium (2317), a lactonohydrolase from Acinetobacter calcoaceticus F46 (2318), and hydroperoxide halolyse from the marine diatom Stephanopyxis turris (2319). The biosynthesis of the ubiquitous methyl halides seems to involve methyl transferase enzymes, which have been isolated and purified in the plant Brassica oleracea (S -adenosyl-L-methionine ... 

Upper repulsive states exist for polyatomic molecules just as they do for diatomic molecules. The alkyl halides all show absorption which corresponds to dissociation into alkyl radicals and halogen atoms. Saturated hydrocarbons absorb only below 1800 A unless rings with considerable strain are present. The first absorption region for the simple alkanes is a continuum and dissociation must immediately follow the absorption act. The simple alcohols also show continua. 

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