Mean collision frequency

The number of molecules escaping per second is equal to this quantity multiplied by the mean collision frequency, that is the mean velocity v divided by the mean free path s. But = JVg s, hence the number of solute molecules reaching the surface per second is ... 

This concludes the theory of collision-induced line shapes of binary systems, that is the line shape that one might observe at gas densities that are not too high - with one exception near zero frequency the intercollisional dip will always be present, no matter how low the pressure may be. The absorption dip is a many-body effect and is not obtainable from a binary theory (Poll 1980). At low gas densities, the intercollisional process appears only over a very small frequency interval near zero, of the order of the mean collision frequency, and it can in general be readily distinguished from the binary profile which extends over a much greater range of frequencies. 

Here, is the mean collision frequency of molecules of the type A with B vc(u) is the collision frequency of molecule A with A s initial speed being v P(v) is the probability density for AB collisions with A s initial speed being v K(v) is the intracollisional spectrum at zero frequency, per collision, with initial speed v A(v) is the mean projection of the integrated dipole moment induced by collisions with initial speeds v on the velocity... 

In looking at plasmas in the most general way, we can categorize phenomena in terms of characteristic parameters. For example, a simple gas can be dealt with in terms of a mean-free path, mean collision frequency, or mean thermal energy. If the mean-free path is less than the dimensions of the vessel holding the gas, it can be treated as a continuum. Otherwise, we would have to look at free molecular flow. In contrast, a plasma has many more characteristic parameters than a simple gas. 

Collision frequencies, mean free paths, and cross sections. Collision processes are central to the description of chemical reactions in the plasma. The mean free path /Ia/b of particle A is the mean distance this particle travels before encountering particle B. AA/b is related to the mean velocity of particle A and to the mean collision frequency between A and B. 

This expression shows that apart from loss of momentum a change in direction may also result from collisions. The mean collision cross section is denoted as collision frequency is described as (o v) r) and a mean collision frequency as [Pg.8]

Thus the transition probability is taken to be local in space and is characterized by a mean collision frequency It follows that the BGK kinetic equation is... 

Z — Height (geometric) above mean sea level in meters T — Temperature in kelvins P — Pressure in pascals (1 Pa = 0.01 millibars) p — Density in kilograms per cubic meter (1 kg/m = 1 g/L) n — Number density in molecules per cubic meter V — Mean collision frequency in collisions per second / — Mean free path in meters... 

Finally, the mean collision frequency v"(z, t) and the corresponding rate coefficient it"(z, i) of the /th excitation or dissociation process are represented by the averages... 

FlO. 6. Mean collision frequencies in the neon and nitrogen plasmas. 

With respect to the application of electron kinetic quantities in an extended quantitative plasma description, the mean collision frequencies v (or the corresponding rate coefficients kf) related to the various inelastic electron collision processes are of particular importance. According to Eq. (29), these mean collision frequencies are determined by the isotropic distribution. The evolution of the various mean collision frequencies with growing field strength is presented in Fig. 6 for the neon (left) and nitrogen (right) plasmas. 

The mean collision frequency for an A molecule in a binary mixture is thus... 

Here E and co denote the strength and frequency of the electric field, respectively. v is the mean collision frequency between electrons and molecules or atoms. For optical frequencies, the relation... 

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