Three body recombination

Electron thermalization Thermal electron capture Reaction of rare gas excited states Cation dimerization Two body ion-ion recombination Three body ion-ion recombination Exciplex fluorescence... 

Keck J 1960 Variational theory of chemical reaction rates applied to three-body recombinations J. Chem. Phys. 32 1035 Anderson J B 1973 Statistical theories of chemical reactions. Distributions in the transition region J. Chem. Phys. 58 4684... 

Heibst, E. In Atomic, Molecular, Optical Physics Handbook Drake, G., Ed. AIP Press New Yoik, 1996, p 429 Adams, N. G. In Atomic, Molecular, Optical Physics Handbook Drake, G., Ed. AIP Press New Yoik, 1996, p 441. For three-body systems, a slightly more complex temperature dependence is observed. For saturated systems, more complex treatments are needed —see Gilbert, R. G. Smith, S. C. Theory erf Unimolecular and Recombination Reactions Blackwell Oxford, 1990. 

B. Three-Body Recombination Involving Long-Lived Complexes.53... 

V. Three-Body Effects in Early Recombination Measurements.73... 

The experiment, however, does not provide conclusive proof for three-body recombination. Perhaps, spectroscopic studies of emissions in recombining plasmas may shed further light on the mechanism. Two interesting observations were made by Amano 56 57 and by Miderski and Gellene.58 They found that H3 (or... 

V. THREE-BODY EFFECTS IN EARLY RECOMBINATION MEASUREMENTS... 

The recombination of He is a special case. We include it here because of the similarities with H3 and because it is the only known example where three-body recombination of a diatomic molecular ion dominates over the binary process. The literature on the helium afterglow is quite large and we will not be able to do justice to all aspects of this problem. Mulliken71 had predicted that fast dissociative recombination of Hej should not occur due to a lack of a suitable curve crossing between the ionic potential curve and repulsive curves of He. Afterglow experiments in pure helium, at sufficient pressure to enable formation of Hej ions, have confirmed this expectation. It does not appear that the true binary recombination... 

C. Three-Body Effects in Recombination of Polyatomic Ions... 

Our discussion of complex formation in electron-ion recombination, field effects, and three-body recombination has perhaps posed more questions than it has answered. In the case of H3 recombination, the experimental observations suggest but do not prove that complex formation is an important mechanism. Three-body recombination involving complex formation is not likely to have much effect on the total recombination coefficients of diatomic ions, but it may alter the yield of minor product channels. Complex formation may be most prevalent in the case of large polyatomic ions, but there is a serious lack of experimental data and theoretical calculations that can be adduced for or against complex formation. 

Our lack of knowledge concerning the mechanisms of molecular recombination has serious consequences for plasma modeling. If the measured data are subject to three-body and field effects, then their application to low-density plasmas (e.g. space plasmas) is questionable. For this reason, studies that focus on recombination... 

However, 03 does not appear to react with CO below 523 K. Since CO is apparently oxidized by the oxygen atoms formed by the decomposition of ozone [the reverse of reaction (3.37)], the reaction must have a high activation energy (>120kJ/mol). This oxidation of CO by O atoms was thought to be rapid in the high-temperature range, but one must recall that it is a three-body recombination reaction. 

Using laser fluorescence measurements on fuel-rich H2/02/N2 flames seeded with H2S, Muller et al. [43] determined the concentrations of SH, S2, SO, S02, and OH in the post-flame gases. From their results and an evaluation of rate constants, they postulated that the flame chemistry of sulfur under rich conditions could be described by the eight fast bimolecular reactions and the two three-body recombination reactions given in Table 8.4. 

The three-body recombination reactions listed in Table 8.4 are significant in sulfur-containing flames because one provides the homogeneous catalytic recombination of the important H2—02 chain carriers H and OH via H + S02 + M HS02 + M... 

Reaction 2-6 is sufficiently fast to be important in the atmosphere. For a carbon monoxide concentration of 5 ppm, the average lifetime of a hydroxyl radical is about 0.01 s (see Reaction 2-6 other reactions may decrease the lifetime even further). Reaction 2-7 is a three-body recombination and is known to be fast at atmospheric pressures. The rate constant for Reaction 2-8 is not well established, although several experimental studies support its occurrence. On the basis of the most recently reported value for the rate constant of Reaction 2-8, which is an indirect determination, the average lifetime of a hydroperoxy radical is about 2 s for a nitric oxide concentration of 0.05 ppm. Reaction 2-8 is the pivotal reaction for this cycle, and it deserves more direct experimental study. 

Step V describes the three-body radical recombination. Finally, step VI includes the three mechanisms of NO production, as well as reburn. 

After the rapid oxidation that typically occurs in a flame sheet, the temperature is high and the concentration of the O and H radicals may be significant. In the postflame region these radicals react in three-body recombination reactions, mainly... 

Beyond a distance of approximately 0.9 mm, the chain-branching reactions achieve a partial-equilibrium condition, in which the forward and reverse rates are essentially equal. At this point the slower three-body recombination reactions can begin to dominate the chemistry, since the fast reactions are nearly equilibrated. 

The only likely source of excitation is the three-body recombination of atomic oxygen in reaction (12), but even if [O] remained at its daytime level, k12 would have to be at least 10"32 cm6 molec"2 sec-1 to account for the observed intensity of the 7620 A band at night (the calculation assumes an emitting layer of 10 km centered94 at 90 km and no nonradiative loss of excited oxygen). For the 1.27 (x band, the appropriate value of k12 would have to be greater than 3 x 10"32 cm6 molec"2 sec"1... 

The strongest piece of evidence for the NO dimer intermediate is the circumstantial one of the similarity between all the known three-body reactions (excluding recombinations) all consist of two nitric oxide molecules reacting with a third molecule 02, Cl2, Br2, and H2. 

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