Sticking probability molecules

If we now assume that this surface at temperature T is in equilibrium with a gas then the adsorption rate equals the desorption rate. Since the atoms/molecules are physisorbed in a weak adsorption potential there are no barriers and the sticking coefficient (the probability that a molecule adsorbs) is unity. This is not entirely consistent since there is an entropic barrier to direct adsorption on a specific site from the gas phase. Nevertheless, a lower sticking probability does not change the overall characteristics of the model. Hence, at equilibrium we have... 

Methane is a stable molecule and therefore hard to activate. As a result the sticking probability for dissociative chemisorption is small, of the order of 10 only, and ruthenium is more reactive than nickel. However, a stretched overlayer of nickel is significantly more active than nickel in its common form, in agreement with expectation. 

The primary process initiating dust surface chemistry is the collision of a molecule from the ISM with the surface. The sticking probability is a measure of how often molecules will stick to the dust surface but this depends on the collision energy, the temperature of the grain surface and the nature of the chemical surface itself. The silicate surface is highly polar, at least for a grain of sand on Earth, and should attract polar molecules as well as atoms. The adsorption process can also be reversed, resulting in thermal desorption, both as the reverse of adsorption and by new molecules as the product of surface reactions. 

The rate of adsorption of CO is equal to the product of the flux of CO molecules striking the surface, F, and their sticking probability, S. That is,... 

Despite the orientational dependence of the sticking probability, at low incident kinetic energies all molecules are reoriented into favorable binding orientations during the collision. However, they might not actually stick. 

In a subsequent study, Agrawal, Raff and Thompson showed that the sticking probability for the molecule was independent of the interactions used for the substrate atoms. The mobility of the H atoms and the rate of energy transfer between the H atoms and the substrate, however, were reported to depend somewhat on the lattice. Despite the small dependence on the substrate model, the major results of the initial study remained unchanged. 

Sticking is a process where a gas molecule collides with a surface and ends in an adsorbed state. There are two interesting aspects of this process, the probability that the molecule is adsorbed and the state of the adsorbed molecule. The probability that an atom or molecule hitting the surface will adsorp is known as the sticking coefficient. If the sticking coefficient is sigma, the adsorption rate is o. ... 

Before we can calculate the sticking probability s and the fraction of surface covered 9 we must derive quantitative expressions for the processes just described. Let L be the number of nitrogen molecules entering the system per second through the leak. The number of molecules leaving the system per second through the pump = 3.8 X W paj,. The number of molecules removed from the volume per second by the filament = 3.8 X 10 pa/s. Let ci = the number of molecules per second accumulating in the volume V. Then ci = 3.2 X lO Vdp/dt. Except in the... 

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