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Physisorption, also called physical adsorption, is a process in which the electronic structure of the atom or molecule is barely perturbed upon adsorption. [ 1 ] [ 2 ] [ 3 ] Overview
BET model of multilayer adsorption, that is, a random distribution of sites covered by one, two, three, etc., adsorbate molecules. The concept of the theory is an extension of the Langmuir theory, which is a theory for monolayer molecular adsorption, to multilayer adsorption with the following hypotheses:
The terms in the bracket give the total partition function of the adsorbed molecules by taking a product of the individual partition functions (refer to Partition function of subsystems). The 1 / N A ! {\displaystyle 1/N_{A}!} factor accounts for the overcounting arising due to the indistinguishable nature of the adsorbates.
Two types of adsorption are recognized: physisorption, weakly bound adsorption, and chemisorption, strongly bound adsorption. Many processes in heterogeneous catalysis lie between the two extremes. The Lennard-Jones model provides a basic framework for predicting molecular interactions as a function of atomic separation. [6]
The function is not adequate at very high pressure because in reality / has an asymptotic maximum as pressure increases without bound. As the temperature increases, the constants k {\displaystyle k} and n {\displaystyle n} change to reflect the empirical observation that the quantity adsorbed rises more slowly and higher pressures are required ...
The freshly sputtered chemically active cathode material acts as a getter that then evacuates the gas by both chemisorption and physisorption resulting in a net pumping action. Inert and lighter gases, such as He and H 2 tend not to sputter and are absorbed by physisorption. Some fraction of the energetic gas ions (including gas that is not ...
Adsorption may occur via physisorption and chemisorption. Ions and molecules can adsorb to many types of surfaces including polymer surfaces. A polymer is a large molecule composed of repeating subunits bound together by covalent bonds. In dilute solution, polymers form globule structures.
Physisorption is characterized by weak van der Waals interactions, and bond enthalpies typically less than 20 kJ/mol. Chemisorption, alternatively, is defined by stronger covalent and ionic bonds, with bond enthalpies between 250 and 500 kJ/mol.