Cross sections Langevin

Intramolecular Isotope Effects. The data in Figure 2 clearly illustrate the failure of the experimental results in following the predicted velocity dependence of the Langevin cross-section. The remark has been frequently made that in the reactions of complex ions with molecules, hydrocarbon systems etc., experimental cross-sections correlate better with an E l than E 112 dependence on reactant ion kinetic energy (14, 24). This energy dependence of reaction presents a fundamental problem with respect to the nature of the ion-molecule interaction potential. So far no theory has been proposed which quantitatively predicts the E l dependence, and under these circumstances interpreting the experiment in these terms is questionable. 

Figure 11. Ratio of experimental values of formation cross-section of CH0 + to calculated Langevin cross-section for collision of CH + with CH as a function of average ion kinetic energy...

The Langevin cross section is a lower limit of computed cross sections. 

EFFECT OF PERMANENT DIPOLE ON LANGEVIN CROSS-SECTION... 

The calcnlated Langevin cross section is about 80 A, so the result appears to be in the correct ballpark. 

Fig. 18. Compilation of cross-section data for the reaction He (N2,He + N)N as a function of the He" ion energy, made by Maier, to which reference should be made for the sources of the data. The long-dashed line is beam data the short-dash/long-dashed line is obtained from stationary afterglow data the solid line refers to longitudinal tandem data and the short-dashed line is the Langevin cross section.

Accordingly, the term Langevin cross section or close-collision cross section is to be preferred over such alternatives as capture cross sec-tion or orbiting cross section/ The former, used correctly... 

Our own approach to this matter has been to avoid the difficulties inherent in making quantitative estimates of molecular size, but to formulate the problem in terms of energies, which are measurable experimentally. Consider a particular collision energy E for which the Langevin cross section cr( ) is given by the familiar expression... 

If the Langevin cross section or any other close-collision cross section is to be used to set an upper bound on the cross section of a charge-transfer reaction, it must be shown, by velocity analysis of the products, or from their angular distribution, that the trajectories responsible did indeed cross the centrifugal barrier. 

The reaction is very exothermic (1.8 eV) with a large Langevin cross section of, and therefore is the dominant ion in a pure hydrogen discharge. 

This is the so-called Langevin cross section, which is frequently used in the discussion of ion-molecule reactions (Dugan and Magee, 1971). 

Similar to the hard-sphere collision model, the capture colhsion cross section or the Langevin cross section is defined as ... 

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