Collision frequency ternary

Summarizing, it may be said that virial expansions of spectral line shapes of induced spectra exist for frequencies much greater than the reciprocal mean free time between collisions. The coefficients of the density squared and density cubed terms represent the effects of purely binary and ternary collisions, respectively. At the present time, computations of the spectral component do not exist except in the form of the spectral moments see the previous Section for details. 

The relative values of the constants a, b, and c can be calculated with some measure of success from the kinetic theory on the assumption that they correspond to the frequencies of ternary collisions. 

Although radiative association has been occasionally studied in the laboratory (e.g., in ion traps ), most experiments are imdertaken at densities high enough that ternary association, in which collision with the background gas stabihses the complex, dominates. A variety of statistical treatments, such as the phase-space theory, have been used to study both radiative and ternary association. These approximate theories are often quite reliable in their estimation of the rate coefficients of association reactions. In the more detailed treatments, microscopic reversibility has been applied to the formation and re-dissociation of the complex. Enough experimental and theoretical studies have been undertaken on radiative association reactions to know that rate coefficients range downward from a collisional value to one lower than lO cm s and depend strongly on the lifetime of the complex and the frequency of photon emitted. The... 

A reaction that involves only one molecular species, such as the dissociation reaction in equation (3.1.3) is referred to as a first order reaction. It is clear from inspection of equation (3.1.3) that in such a case the rate constant, k 2, must have the dimensions of reciprocal time (s ) (i.e. of frequency). A reaction that involves the encounter of two reactant molecules, such as the association reaction in equation (3.1.2), is referred to as a second order reaction. Inspection of (3.1.2) shows that the rate constant in this case must have the dimensions of 1/(concentration x time), e.g. it will be measured in units of M s when concentration is expressed in molar (M) units. Genuine reactions with order greater than two are rare and will not be dealt with here they would require ternary collisions, which are likely to have very low probabilities. 

The frequency of trimolecular (ternary) collisions also may be estimated for an ideal gas, subject to the restrictions mentioned earlier." For the simultaneous collision of A, B, and C, the result is... 

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