Adsorption complexes, geometry

Figure 11. Fully optimized 3-21G donor adsorption complex geometry.

Figure 12. (a) f ully optimized 3-21G acceptor adsorption complex geometry, (b) Fully optimized M P2/6-31G acceptor adsorption complex geometry. 

The geometry of the ensembles of A atoms in the surface can, however, influence the adsorption complexes not only by changing the number of single bonds to different atoms of the adsorbed molecule, as illustrated above a second type of ensemble effect can be visualized for any given atom of the adsorbate. Taking the adsorption complexes of CO on a transition metal as an example, we can discern linear, bridged, and multisite complexes ... 

In this chapter, recent results are discussed In which the adsorption of nitric oxide and its Interaction with co-adsorbed carbon monoxide, hydrogen, and Its own dissociation products on the hexagonally close-packed (001) surface of Ru have been characterized using EELS (13,14, 15). The data are interpreted In terms of a site-dependent model for adsorption of molecular NO at 150 K. Competition between co-adsorbed species can be observed directly, and this supports and clarifies the models of adsorption site geometries proposed for the individual adsorbates. Dissociation of one of the molecular states of NO occurs preferentially at temperatures above 150 K, with a coverage-dependent activation barrier. The data are discussed in terms of their relevance to heterogeneous catalytic reduction of NO, and in terms of their relationship to the metal-nitrosyl chemistry of metallic complexes. 

In a weakly bonded (by 4.5 kcal/mol) adsorption complex neither the geometry of the methane molecule nor the conformation of the center undergo any significant relaxation. Since the adsorption of methane has been found very weak the stability of the complex has been confirmed by independent semiempirical calculations. The adsorption distance... 

The theoretical results obtained in the present work, strongly support the conclusions of Sheppard [46] and of Lehwald et al [67]. The results in Table 10 show that the molecule binds strongly on a Ni(lOO) surface, the geometry and the electronic structure of the molecule are highly perturbed by the adsorption process, and the di-CT adsorption mode is more stable than the 7t mode, by approximately 91 kJmoT. The calculated CC bond length for the di-a mode, 1.46 A, is identical to the experimental value determined by NEXAFS [68]. An analysis of the electronic structure shows that on both adsorption complexes the degree of the [Pg.236]

The geometry of the adsorption complex formed by Na ion and propene is shown in Figure 7. The distances between the carbon atoms involved in the double bond and the sodium ion are 2.623 and 2.531 A. The out-of-plane angle of the sodium ion from the plane of three O3 atoms was 30.8°. It is worth comparing the total energies of these two adsorption... 

Figure 6. The optimized geometry of the cyclopropane adsorption complex.

Figure 2. (a) A typical representative dimer cluster model showing the bridging oxygen site, 04. (b) The geometry of the dimer cluster-ammonia adsorption complex. 

Boese and Foerster [596] found pronounced similarities in the adsorption behavior and IR spectroscopic features of isoelectronic molecules such as N2 and CO (or CO2 and N2O, vide infra). For calculations, an electrostatic interaction model was used. As mentioned above, the cations were identified as the centers of adsorption, since the main potential wells were found in front of them. Also, the geometry of the adsorption complexes was shown to be similar (cf. Fig. 34). 

A variety of methods have also been used to relate the observed bond strengths of cation-adsorbate interactions to the locations of cations within the pore space, the structure of the adsorption complex and its relation to the geometry of the pores. IR, NMR and diffraction are the most important experimental methods. Computational approaches have also been successful, although these have the added difficulty of modelling the location of the framework charge and cation locations. 

The successes enjoyed by nanosciences in many fields [2-10] have resulted in a need for adequate theory and large-scale numerical simulations in order to understand what the various roles are played by surface effects, edge effects, or bulk effects in nanomaterials. The dynamics of colloidal particle transport calls not only for passive transport, but also for additional processes such as agglomeration/dispersion, driven interfaces, adsorption to pore wall grains, and biofihn interactions [4,11-14]. In many cases, there is a dire need to investigate these multi-scale structures, ranging from nanometers to micrometers in complex geometries, such as in vascular and porous systems [4,15-17]. 

The structure of the adsorbate systems formed by mercaptobenzothiazole and analogue molecules on CdS (1010) surface was studied quantum chemically using density functional theory [57]. Preliminary calculations of the free adsorptive molecules indicate an energetic preference of their thione form compared to the thiol form. For the anions of the adsorptive molecules, the role of the endocyclic nitrogen and the exocychc sulfur as possible donor atoms was examined by means of known chelate complexes. Geometry optimizations showed that the structure of the adsorbate systems is dominated by the formation of two coordinative bonds from the donor atoms of the adsorptive anions to two adjacent Cd atoms of the surface. It showed that the molecular plane of the adsorptives is tilted with respect to the normal of the crystal face. They have shown that the tilt angle is mainly determined by the tendency of the surface Cd atoms to continue the tetrahedral coordination from the bulk [57]. 

NMR spectroscopy allows the determination of the geometry of adsorption complexes and of the mobility of the probe molecules. This will be demonstrated for CO molecules adsorbed on bridging hydroxyl groups. 

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