Bonding surface group orbital

The fact that or + is not a discrete level but the maximum local density distribution of the surface group orbital reduces the coupling between adsorbate orbital ao and surface orbital a + n. In order to compute the bond strength we have to return to Eq.(2.229b) ... 

In contrast to the preference for high coordination of adsorption of atoms as C, O, or N, the CO molecule generally prefers low-coordination sites. This is due to the different preferences of the HOMO and LUMO interactions for low and high coordination, respectively. The chemical bonding aspects that are basic to this phenomenon are discussed in detail in the next part of this subsection and also the following section on surface group orbitals. 

A similar process occurs on the ensemble of surface atoms that activates dissociation of a molecular k bond. Then, the antibonding unoccupied orbital of the molecule has to interact with surface group orbitals of similar symmetry on the ensemble of surface atoms. When the unoccupied molecular orbital becomes... 

The situation is different for the ir-symmetry interaction. With respect to the unoccupied CO 2x orbitals, the surface metal orbitals behave as bonding orbitab. Since the shift downward is larger in bridge coordination (the asymmetric group orbital has a maximum at higher energy) than atop, the 2ir orbitals prefer bridge coordination. 

For NH3 adsorption to Cu in two-fold coordination (Fig. 3.4) an analysis of the surface chemical bonds has been made with the surface orbital densities decomposed according the corresponding group orbitals. One notes the density of states at lower energies as well as the lower energy position of bonding and antibonding interactions for two-fold coordination compared to one-fold coordination. 

The bond energy does not relate to the bandwidths of the broadened levels, but to the group orbital local density of states at the Fermi level projected out from the surface eigenfunctions by the adsorbate orbitals. 

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