Orbital hybridization at surfaces

Atomic Orbital Hybridization at Surfaces Hydration Energies 

The hybridization of the Ir d- states with the Cu sp- states yields in tilted pd- orbitals located at the neighbored Cu atoms. Because of the tilt, the charge density maximum, which is for pure Cu( 100) right above the Cu surface atom, shifts to the position above the Cu sub-surface atom. As a consequence, in case of a fcc(lOO) surface, the charge density depletion above buried Ir atoms in combination with a higher intensity aside of the first layer Cu atoms results in the star-like pattern obtained in the experiment (Fig. 13a) and theory (Fig. 15) 

This part has verified up two concepts that should be of immediate application. One is the rp-orbit hybridization of the electronegative adsorbate as a charge acceptor and the other is the bond contraction of the host surface. Table 8.1 features functionalities and potential applications of the bonding events. The bond contraction is not limited to an oxide surface, but it happens at any site, where the atomic CN is lower than the bulk standard. 

For each of the two resonance forms, the central O atom is sp2 hybridized with one unhybridized p atomic orbital. The sp2 hybrid orbitals are used to form the two ar bonds to the centra) atom. The LE view of the 77 bond uses unhybridized p atomic orbitals. The 77 bond resonates between the two positions in the Lewis structures. In the MO picture of the tt bond, all three unhybridized p orbitals overlap at the same time, resulting in 77 electrons that are delocalized over the entire surface of the molecule. 

It can be imagined that the bonds can be broken at any location, that is, with an oxygen, hydroxy, silicon, or aluminum exposed. In this case, it could further be imagined that s-, p-, and sp3-hybridized orbitals would be on the surface. This 

As is seen in Fig. 33 c, the maximum in LDOS of the asymmetric LDOS (dye) is at higher energy than that of the symmetric part (dcr). After hybridization, the surface orbitals can be represented as sketched in Fig. 33 b. 

We have emphasized the importance of open d-orbitals and a proper atomic state if should dissociate with a low barrier on a transition metal surface. For clusters, however, the same type of dissociation puts up another requirement, which will turn out to be even more significant in the present context There must be at least one open shell valence orbital (of s-character) on the cluster, otherwise the sd-hybridization will not take place (8). For an infinite surface, this requirement can always be satisfied since states with open valence orbitals must at least be reachable by a low energy excitation. For clusters, the same type of excitation may be much more expensive. Since all nickel clusters dissociate it seems clear that a dissociative state is reachable in all cases for nickel. The question that has worried us for the past years is why the same type of states do not always seem reachable for iron and cobalt clusters. The answer to this question is discussed in section VI. 

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