Physisorption: Difference between revisions

This [[Pauli exclusion]] and repulsion are particularly strong for atoms with closed valence shells that dominate the surface interaction. As a result, the minimum energy of physisorption must be found by the balance between the long-range van der Waals attraction and short-range [[Pauli repulsion]]. For instance, by separating the total interaction of physisorption into two contributions—a short-range term depicted by [[Hartree&ndash;Fock]] theory and a long-range van der Waals attraction—the equilibrium position of physisorption for rare gases adsorbed on [[jellium]] substrate can be determined.<ref name="Kohn">{{Citation | author=E. Zaremba and W. Kohn|title= Theory of helium adsorption on simple and noble-metal surfaces| journal= Phys. Rev. B| volume=15 | issue=4 | pages= 1769–1781| year=1977 | doi=10.1103/PhysRevB.15.1769|bibcode = 1977PhRvB..15.1769Z }}</ref> Fig. 2 shows the physisorption potential energy of He adsorbed on Ag, Cu, and Au substrates which are described by the [[jellium]] model with different densities of smear-out background positive charges. It can be found that the weak van der Waals interaction leads to shallow attractive energy wells (<10&nbsp;meV). One of the experimental methods for exploring physisorption potential energy is the scattering process, for instance, inert gas atoms scattered from metal surfaces. Certain specific features of the interaction potential between scattered atoms and surface can be extracted by analyzing the experimentally determined angular distribution and cross sections of the scattered particles.

 

 

<math>\theta=(\chi-\chi_\text{c})U(\chi-\chi_\text{c})</math>

* The elementary step in physisorption from a gas phase does not involve an [[activation energy]]. Chemisorption often involves an activation energy.

* For physisorption gas phase molecules, adsorbates, form multilayer adsorption unless physical barriers, such as porosity, interfere. In chemisorption, molecules are adsorbed on the surface by valence bonds and only form monolayer adsorption.

* Another way of looking at this is that chemisorption alters the <u>topology</u> of the electrons in the adsorbate molecule (by the process of chemical reaction) but physisorption does not.

==See also==

*[[Adsorption]]

==References==

{{reflist}}

 

[[Category:Surface science]]