Electron distributions metal surface energy

Fig. 3. Vibrational population distributions of N2 formed in associative desorption of N-atoms from ruthenium, (a) Predictions of a classical trajectory based theory adhering to the Born-Oppenheimer approximation, (b) Predictions of a molecular dynamics with electron friction theory taking into account interactions of the reacting molecule with the electron bath, (c) Born—Oppenheimer potential energy surface, (d) Experimentally-observed distribution. The qualitative failure of the electronically adiabatic approach provides some of the best available evidence that chemical reactions at metal surfaces are subject to strong electronically nonadiabatic influences. (See Refs. 44 and 45.)...

Solvent and other contributions to the surface energy that are independent of x2 need not be considered, since the surface energy is used only to find x2 by minimization. It is assumed that no change in the electronic structure of the metal-ion cores or in their distribution occurs during charging. 

Based on the first-principles study of helium adsorption on metals (Zaremba and Kohn, 1977), Esbjerg and Nprskov (1980) made an important observation. Because the He atom is very tight (with a radius about 1 A), the surface electron density of the sample does not vary much within the volume of the He atom. Therefore, the interaction energy should be determined by the electron density of the sample at the location of the He nucleus. A calculation of the interaction of a He atom with a homogeneous electron distribution results in an explicit relation between the He scattering potential V r) and the local electron density p(r). For He atoms with kinetic energy smaller than 0.1 eV, Esbjerg and Nprskov (1980) obtained... 

Mercury is not a typical electrode material it is liquid, and there is constant movement of atoms on the surface in contact with solution. A solid electrode has a well-defined structure, probably polycrystalline and in some cases monocrystalline. In a solid metallic electrode conduction is predominantly electronic owing to the free movement of valence electrons, the energy of the electrons that traverse the interface being that of the Fermi level, EF (Section 3.6), giving rise to effects from the electronic distribution of the atoms in the metallic lattice already mentioned. 

Three other observations from the work of Brill and Tauster (241) are noteworthy. The loss of activity of both catalysts after exposure to a pulse of poison was very slow (on the order of 10-100 hr), suggesting that the sulfur was preferentially adsorbed at the entrance to the bed and then diffused slowly through the bed until the poison was uniformly distributed. The activation energy for unpoisoned and partially poisoned catalysts (both promoted and unpromoted) was the same (96 kJ/mol), suggesting that the poisoning involves a blocking of iron sites, rather than a modification of the electronic properties or Fermi level of the metal. Moreover, a linear dependence between the rate constant and the square of the concentration of unpoisoned surface was observed (Fig. 36), suggesting that two iron sites were poisoned by each adsorbed sulfur in the promoted catalyst. 

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