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Bridge site

Figure 5 shows the utility of HREELS in establishing the presence of both bridge-bonded and atop CO chemisorbed on Pt(l 11) and two SnPt alloy surfaces, and also serves to emphasize that HREELS is very useful in studies of metal alloys. The v o pc ks for CO bonded in bridge sites appear at 1865, 1790, and 1845 cm on the Pt(lll), (2 x 2) and 3 surfaces, respectively. The VCO peaks for CO... [Pg.452]

The associative part of the adsorbing potential, Eq. (116), generates a highly localized adsorption which corresponds to the onefold, to the twofold bridging site, and to the fourfold hollow site adsorption dependence of the length L. Note that in the absence of the associative part, Eq. (119), and in the limit 0 the pore walls reduce to an array of hard spheres. [Pg.208]

FIG. 5 Schematic of site parameters and interactions employed for the hollow-bridge site model of Te on W(IOO). Also depicted are the six hollow sites (squares) and adjacent bridge sites (small open circles) allowed in one strip in the construction of the transfer matrix. (Reprinted from Ref. 37 with permission from Elsevier Science.)... [Pg.457]

Figure 2 Models for the carbon-terminated 3C-SiC(001)c(2x2) surface (a) staggered C=C-dimer model, (b) C2 groups in Si bridge sites. Cf. text. Figure 2 Models for the carbon-terminated 3C-SiC(001)c(2x2) surface (a) staggered C=C-dimer model, (b) C2 groups in Si bridge sites. Cf. text.
Definitions of the most common adsorption sites are shown in Fig. 5.5. They are named on-top site, bridge sites (long or short bridge), and hollow sites, which may be three-fold or four-fold in character. In case of three-fold adsorption on the fcc(lll) surface it is also necessary to distinguish between hep and fee sites, having an atom just below the site or not. [Pg.171]

In calculating the metallic surface area, one has to take proper care of the reaction stoichiometry. In the ideal case, a molecule occupies one site, as shown for terminal adsorbed CO in Fig. 3.46.a. Alternatively, a molecule may chemisorb on more than one metal atom, as shown in Fig. 3.46.b and c for bridged-site adsorbed CO and in Fig. 3.46.d for valley-site adsorbed CO, respectively. In some specific cases of really big molecules, one can imagine that a molecule adsorbs on only one site, while simultaneously blocking adjacent sites for geometric reasons. In case an adsorbate molecule adsorbs dissociatively, it will occupy more than one site as shown in Fig. 3.46.e. [Pg.102]

Zhang CJ, Hu P. 2000. Why must oxygen atoms be activated from hohow sites to bridge sites in catalytic CO oxidation J Am Chem Soc 122 2134-2135. [Pg.128]

Figure 5.4 Coadsorption of a 30 1 ammonia-oxygen mixture at a Cu(110) surface at 290 K with the formation of well ordered c(2 x 4) imide chains running in the < 110 > direction. The separation between the rows is 7.2 A and within the rows 5.1 A, the NH species occupying the bridge sites. (Reproduced from Ref. 11,39). Figure 5.4 Coadsorption of a 30 1 ammonia-oxygen mixture at a Cu(110) surface at 290 K with the formation of well ordered c(2 x 4) imide chains running in the < 110 > direction. The separation between the rows is 7.2 A and within the rows 5.1 A, the NH species occupying the bridge sites. (Reproduced from Ref. 11,39).
Any proposed mechanism for the unprecedented transformation described by Equation 18 must account for the promotion of this photoisomerization by CO, although CO is not required by the stoichiometry. A possible initial step would be similar to that for the Ru3(CO)i2 fragmentation (Scheme 1). In this a Ru-Ru bond is broken concomitant with the movement of a CO from a terminal to a bridging site to form an unsaturated intermediate analogous to I. A speculative proposal along these lines is presented in Figure 5. The key feature of this proposal would be the formation of III with one unsaturated ruthenium, which could be captured by CO to promote the subsequent steps leading from the /1-methylidyne to the acyl... [Pg.137]

The staining of germinated pollen of Hippeastrum hybridum with colchicine demonstrates green-yellow emission of microtubules (better vision in black-white image) around nuclei of pollen grain (threads at the division of the nucleus) and spermium on the tip of the pollen tube, where spermium moves, as well as in some bridge sites of the tube (Fig. 10). The similar fluorescent allelochemicals may be also used as fluorescent dyes at the cellular diagnostics (Roshchina, 2005 b). [Pg.121]

For an fee lattice a particularly simple surface structure is obtained by cutting the lattice parallel to the sides of a cube that forms a unit cell (see Fig. 4.6a). The resulting surface plane is perpendicular to the vector (1,0,0) so this is called a (100) surface, and one speaks of Ag(100), Au(100), etc., surfaces, and (100) is called the Miller index. Obviously, (100), (010), (001) surfaces have the same structure, a simple square lattice (see Fig. 4.7a), whose lattice constant is a/ /2. Adsorption of particles often takes place at particular surface sites, and some of them are indicated in the figure The position on top of a lattice site is the atop position, fourfold hollow sites are in the center between the surface atoms, and bridge sites (or twofold hollow sites) are in the center of a line joining two neighboring surface atoms. [Pg.43]


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See also in sourсe #XX -- [ Pg.43 , Pg.45 ]

See also in sourсe #XX -- [ Pg.62 ]




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