Promoter site Quantum mechanics

A massive electron transfer between the metal particles and the supports (or promoters) and the penetration of an electric field into the metal are thus not realistic ideas on the through-the-metal interaction. However, there is one mechanism for such an interaction which is well supported by the quantum theory of chemisorption when a covalent chemisorption bond is formed, it causes periodic variation (with the distance) in the chemisorption bond strength in its environment. At the nearest site a repulsion is felt, on the next-nearest an attraction, etc. [46a]. However, it is important to realize how strong this interaction is. A realistic estimate, based on observations of the field ion emission images, shows that these interactions are comparable in their strength to the physical (condensation) van der Waals forces [46b]. 

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