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The langmuir (symbol: L) is a unit of exposure (or dosage) to a surface (e.g. of a crystal) and is used in ultra-high vacuum (UHV) surface physics to study the adsorption of gases. It is a practical unit, and is not dimensionally homogeneous, and so is used only in this field. It is named after American physicist Irving Langmuir.
The adsorption sites (heavy dots) are equivalent and can have unit occupancy. Also, the adsorbates are immobile on the surface. The Langmuir adsorption model explains adsorption by assuming an adsorbate behaves as an ideal gas at isothermal conditions. According to the model, adsorption and desorption are reversible processes.
Plasma oscillations, also known as Langmuir waves (after Irving Langmuir), are rapid oscillations of the electron density in conducting media such as plasmas or metals in the ultraviolet region. The oscillations can be described as an instability in the dielectric function of a free electron gas .
The Hertz–Knudsen equation describes the non-dissociative adsorption of a gas molecule on a surface by expressing the variation of the number of molecules impacting on the surfaces per unit of time as a function of the pressure of the gas and other parameters which characterise both the gas phase molecule and the surface: [1] [2]
Langmuir suggested that adsorption takes place through this mechanism: +, where A is a gas molecule, and S is an adsorption site. The direct and inverse rate constants are k and k −1 . If we define surface coverage, θ {\\displaystyle \\theta } , as the fraction of the adsorption sites occupied, in the equilibrium we have:
The Langmuir-Rideal mechanism is often, incorrectly, attributed to Dan Eley as the Eley-Rideal mechanism. [5] The actual Eley-Rideal mechanism, studied in the thesis of Dan Eley and proposed by Eric Rideal in 1939, was the reaction between a chemisorbed and a physisorbed molecule. [ 6 ]
Langmuir, an academic journal on colloids, surfaces and interfaces, published by the American Chemical Society; Langmuir (unit), a unit of exposure of an adsorbate/gas to a substrate used in surface science to study adsorption; Langmuir Cove, a cove in the north end of Arrowsmith Peninsula, Graham Land, Antarctica
The equation is also known as the "three-halves-power law" or the Child–Langmuir law. Child originally derived this equation for the case of atomic ions, which have much smaller ratios of their charge to their mass. Irving Langmuir published the application to electron currents in 1913, and extended it to the case of cylindrical cathodes and ...
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