Atomic chemisorption, cluster

Sellers H 1991 On modeling chemisorption processes with metal cluster systems. II. Model atomic potentials and site specificity of N atom chemisorption on Pd(111) Chem. Phys. Lett. 178 351-7... 

Wang L S, Wu FI and Desai S R 1996 Sequential oxygen atom chemisorption on surfaces of small iron clusters Phys. Rev. Lett. 76 4853... 

Table IV. Changes in the Mulliken populations of the valence orbitals (relative to the bare Nii7 cluster) and resulting atomic charges due to the formation of the chemisorption clusters NiirNa and Ni K...

Figure 5. Chemisorption reactivity of (a) V and (b) Nb clusters toward Dj as a function of number of atoms in cluster. (From Kaldor et al. )... 

In the final section, we will survey the different theoretical approaches for the treatment of adsorbed molecules on surfaces, taking the chemisorption on transition metal surfaces, a particularly difficult to treat yet extremely relevant surface problem [1], as an example. Wliile solid state approaches such as DFT are often used, hybrid methods are also advantageous. Of particular importance in this area is the idea of embedding, where a small cluster of surface atoms around the adsorbate is treated with more care than the surroundmg region. The advantages and disadvantages of the approaches are discussed. 

Figure 2.14. The molecular orbitals of gas phase carbon monoxide, (a) Energy diagram indicating how the molecular orbitals arise from the combination of atomic orbitals of carbon (C) and oxygen (O). Conventional arrows are used to indicate the spin orientations of electrons in the occupied orbitals. Asterisks denote antibonding molecular orbitals, (b) Spatial distributions of key orbitals involved in the chemisorption of carbon monoxide. Barring indicates empty orbitals.5 (c) Electronic configurations of CO and NO in vacuum as compared to the density of states of a Pt(lll) cluster.11 Reprinted from ref. 11 with permission from Elsevier Science.

One of the m jor attractions in the metal-atom synthesis of dimer and cluster species is the ability to isolate highly unsaturated species, M Lm, that may then be considered to be models for chemisorption of the ligand, L, on either a bare, or a supported, metal surface (,100). It is quite informative to compare the spectral properties of these finite cluster-complexes to those of the corresponding, adsorbed surface-layers (100), in an effort to test localized-bonding aspects of chemisorption, and for deciphering UPS data and vibrational-energy-loss data for the chemisorbed state. At times, the similarities are quite striking. 

The Characterization and Properties of Small Metal Particles. Y. Takasu and A. M. Bradshaw, Surf. Defect. Prop. Solids p. 401 1978). 2. Cluster Model Theory. R. P. Messmer, in "The Nature of the Chemisorption Bond G. Ertl and T. Rhodin, eds. North-Holland Publ., Amsterdam, 1978. 3. Clusters and Surfaces. E. L. Muetterties, T. N. Rhodin, E. Band, C. F. Brucker, and W. R. Pretzer, Cornell National Science Center, Ithaca, New York, 1978. 4. Determination of the Properties of Single Atom and Multiple Atom Clusters. J. F. Hamilton, in "Chemical Experimentation Under Extreme Conditions (B. W. Rossiter, ed.) (Series, "Physical Methods of Organic Chemistry ), Wiley (Interscience), New York (1978). 

Gas phase experiments show that the reactivity of small clusters varies greatly with cluster size (H), and experimental work with small clusters on supports has shown (12) that adsorbed molecules or atoms affect the metal-metal bond length. In both experiments the adsorption site is not known. Also the reactions proceed to completion so that only the high coverage case has been measured. We have considered the chemisorption of several atoms on Be 13 and AI13 clusters. For both clusters trigonal symmetry is maintained, and only the metal-metal... 

Figure 2. The BeisXe D3/1 cluster used to model chemisorption into the four-fold hollows. The Be 13X3 cluster used to model chemisorption into the three-fold hollows is generated by a 60° rotation of the six adsorbate atoms about the vertical axis. The D3d metal cluster is formed by rotating the bottom three metal atoms by 180° about the vertical axis.

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