Interstitial light atom

George SJ, Igarashi RY, Xiao Y, et al. Extended X-ray absorption fine structure and nuclear resonance vibrational spectroscopy reveal that NifB-co, a FeMo-co precursor, comprises a 6Fe core with an interstitial light atom. J Am Chem Soc. 2008 130 5673-80. 

Metal Clusters Including an Interstitial light Atom Other than Hydrogen... 

We felt it worthwhile to provide some level of theoretical overview given the number of DFT studies that have appeared recently and here limit the discussion to theoretical studies that have included an interstitial light atom in consideration of the FeMoco structure. Three of the most recent and comprehensive... 

Fig. 10-1.—Structure of tetragonal boron as viewed in the direction of the c axis. One unit cell is shown. Two of the icosahedral groups (light lines) are centered at z , and the other two (heavy lines) at. The interstitial boron atoms (open circles) are at (0, 0, 0) and (j, ). Numbers identify...

A similar investigation 24> has shown that the annealing process consists in the recombination of a Ge vacancy and an interstitial Ge atom. The rate of this recombination may be strongly influenced by light absorption. 

For instance, Romero-Rossi and Stone (75) who studied the CO oxidation in the presence of ZnO, have shown CO not to be chemisorbed in the dark, whereas under the influence of ultraviolet light, CO forms a strong bond with the surface by capturing the created positive hole. They propose a reaction mechanism where one of the steps is the recombination COads" + Oada —>COa in this hypothesis the chemisorbed reactants behave like recombination centers for the excess free carriers. These authors have also observed that the irradiation does not exert any influence upon the catalytic activity of certain zinc oxides which contain a great excess of interstitial zinc atoms. They explain this fact, which has been experimentally confirmed by Barry and Roberts 20), by admitting a competition between CO molecules and interstitial zinc atoms, for the capture of the positive holes. 

Fig. 5. Vacancies (dark circles) and self-interstitials (light circles) produced by irradiation in Cu by a 20 keV Cu atom and W by a 30 keV W atom. Notice the lack of clustering in the W case.

Many metal carbonyl clusters have interstitial atoms or groups located in the eenter of the polyhedron. Such interstitial atoms may be a light atom sueh as boron, carbon, or nitrogen a post-transition element such as germanium, tin, or antimony or a transition metal. Interstitial atoms most frequently provide all of their valence electrons as skeletal electrons since all of their valence orbitals are neeessarily internal orbitals because of the location of the interstitial atom in the center of the polyhedron. Exceptions to this rule may occur when some of the valence electrons of the interstitial atom occupy orbitals of symmetries which cannot mix with any of the molecular orbitals arising from the polyhedral skeletal bonding. 

On the basis of recent electron-nuclear double resonance (ENDOR) studies, Hoffman and Seefeldt suggested that the interstitial X-atom is not exchanged during catalysis [20, 21]. This would seem to suggest that the X-atom, even if it is a nitride, is not derived from N2 during turnover. Most recently, Hoffman and Seefeldt have gone further in their analysis and have proposed that the central light atom is not an N-atom [21]. They noted a loss of electron... 

The electron can be trapped, for example by an interstitial which is converted to an H atom. The AlO is the hole color center which absorbs light and gives the color to smoky quart2. Bleaching is the result of thermal energy releasing the trapped electron, which then produces the reverse of reaction 1. The amethyst color center in quart2 is exactly like the smoky, except that Fe " replaces. ... 

The influence of light causes changes similar to that occurring in a photographic emulsion. The photons liberate electrons and these are trapped by interstitial silver ions, which exist as Frenkel defects, to form neutral silver atoms. Unlike the photographic process, the electrons are liberated by the Cu+ ions, which are converted to Cu2+ ions (CuAg) in the process ... 

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