Charge-exchange process

There are two basic physical phenomena which govern atomic collisions in the keV range. First, repulsive interatomic interactions, described by the laws of classical mechanics, control the scattering and recoiling trajectories. Second, electronic transition probabilities, described by the laws of quantum mechanics, control the ion-surface charge exchange process. 

Table II must be used with care in anomalous cases in which the transition probability for ionization of the molecule is very low in some energy ranges (e.g., acetylene, benzene, methylamine). In such cases higher RE s, not included in the table and normally of small importance, may be responsible for the charge exchange processes although with small cross-sections (cf. 9, 13).

If no transfer of translational energy occurs, then the charge exchange process probably takes place when the distance between the ion and the molecule is large. This means, however, that the ion and the molecule can be considered as isolated from each other, and therefore, the recombination process of the ion and the ionization process of the molecule must obey the spectroscopic transition laws. On the other hand, if a large transfer of translational energy takes place, then the process probably takes place when the distance is small, and possibly then all selection rules break down. 

If a charge exchange process, A + + B- A -f- B +, occurs when the distance between the two particles is large, we expect that no transfer of translational energy takes place in the reaction and that the same selection rules govern the ionization as in spectroscopic transitions. This means that if the molecule B is in a singlet state before the ionization, the ion B + will be formed in a doublet state after ionization of one electron without rearrangements of any other electrons, at least for small molecules. 

Two main processes—simple charge exchange and ion-molecule reactions—substantially alter the properties of the discharge. The simple charge exchange processes occur between the ionic species and... 

Vanleerdam GC, Lenssen KMH, Btongersma HH. 1990. Charge-exchange processes in low-energy He ion-scattering from Si and Pd2Si Surfaces. Nucl Instrum Meth B 45 390-393. 

In silane discharges several ions are observed to be involved in a charge exchange process, and therefore maxima in their ion energy distribution at distinct energies are observed. The charge carrier density and the plasma potential that result from the fit of the lED allow for the quantification of the related parameters sheath thickness and ion flux. This method has been be used to relate the material quality of a-Si H to the ion bombardment [301. 332] see also Section 1.6.2.3. 

Charge exchange processes as discussed above are important for a good understanding of LEIS, and of SIMS as well. Unfortunately, the subject is still not yet completely understood, which forms an impediment to quantitative analysis by both techniques. Quantitative interpretation of LEIS spectra is nevertheless perfectly possible if one uses appropriate calibration standards. 

Section 4 describes the atoms consisting of 7r+ and 7r mesons (A2v) and experiments involving their detection and lifetime measurement. The lifetime of A2jt is determined by the charge-exchange process... 

The lifetime t of A2v with the principal quantum number n and l = 0, is determined by the charge-exchange process 7r+7r- —> ir°n° and, at the leading order of isospin breaking, may be described through the 5-wave irir scattering lengths ap and a2 with isospin values 0 and 2 [13,14] ... 

Thus, besides the direct photoionization, the analytes in positive APPI mode are ionized either by charge exchange or by proton transfer. The direct ionization and the charge exchange processes allow the ionization of non-polar compounds. This is not possible either with APCI or ESI. 

The peak heat load to the divertor plate is supposed to be limited with the help of impurity radiation and charge exchange processes. Both, photons and charge exchange neutrals, are not affected by the magnetic field, thus allow to distribute the power on the whole vessel surface. 

The efficiency of equilibrium isothermal plants as shown in Figures A.l and A.2 is 100%. Such plants are reversible and free of losses, because of the use of charge exchange processes. 

Harvard University ber/November 2005 charge exchange processes and therefore isothermal oxidation. That is a major leap forward for the industry. See also the two documents by Weibel etal. (2005a, b) for a much more detailed description. 

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