Recombination of atoms

Hardy and Linnett (59) studied the heterogeneous recombination of atomic hydrogen at room temperature on nickel and nickel alloy foils. They did not find any similarity to the behavior of palladium and its alloys with gold studied earlier (35). There was no evidence that, as a result of exposure to atomic hydrogen, hydride was formed in any metal catalyst investigated with a resulting change in the activity of the initial parent metal catalysts. 

On the basis of information on the properties of the nickel-hydrogen and nickel-copper-hydrogen systems available in 1966 studies on the catalytic activity of nickel hydride as compared with nickel itself were undertaken. As test reactions the heterogeneous recombination of atomic hydrogen, the para-ortho conversion of hydrogen, and the hydrogenation of ethylene were chosen. 

The coefficient of recombination of atomic hydrogen on nickel was about one order of magnitude higher than on nickel hydride at the same temperature. Even a partially decomposed hydride was still as inactive as the original hydride sample. 

Chapter 4 deals with several physical and chemical processes featuring various types of active particles to be detected by semiconductor sensors. The most important of them are recombination of atoms and radicals, pyrolysis of simple molecules on hot filaments, photolysis in gaseous phase and in absorbed layer as well as separate stages of several catalytic heterogeneous processes developing on oxides. In this case semiconductor adsorbents play a two-fold role they are acting botii as catalysts and as sensitive elements, i.e. sensors in respect to intermediate active particles appearing on the surface of catalyst in the course of development of catal rtic process. 

According to [ 1 ], in the case of recombination of atoms and radicals governed by the first-order kinetics, the radicals concentration distribution over the height A in a cylindrical vessel can be written as... 

In the first place attention is called to the fact that Bonhoeffer s measures of the rate of recombination of atomic hydrogen at 0.5 mm. fit exactly the law... 

Ozone is main component in many oxidation processes assembled imder the term ozonation processes. In these processes ozone is applied either alone (O3 process) or with the addition of oxidant, e.g. H2O2 (O3/H2O2 process), UV radiation (explained in above subchapter), catalyst, activated carbon, ultrasoimd etc. Ozone is inorganic molecule constituted by three atoms of oxygen. It is present in nature in upper atmosphere in the form of stratospheric layer aroimd the earth, and it is formed by the photolysis of diatomic oxygen and further recombination of atomic and diatomic oxygen, shown by equations (25) and (26) [35] ... 

The result is that for minimum activation energy, the bond YZ must be stretched and weakened before the final bond XY is established. Quantitative calculations show that the activation energy evaluated in this manner amounts, at the most, to 7 % of the bond energy YZ. In accordance with this theory, recombinations of atoms of hydrogen, nitrogen, oxygen, chlorine on metal surfaces... 

The velocity will thus vary as the min power of the gas pressure. In the case of the dissociation of hydrogen molecules into atoms at the surface of a hot metal wire Langmuir found mln =, whilst for the recombination of atoms at a surface min was found to be 2. 

Chemical reactions consist of the combination or recombination of atoms, in fixed ratios, to produce new species. 

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 recombination of atomic oxygen in the presence of a third body M (only N2 and 02)... 

RECOMBINATION OF ATOMS WITH EXCITATION OF THE THIRD BODY... 

The translational temperature Tt plays an important kinetic role. At high temperatures chemical reactions are fast, and — in view of the decreasing rate of surface recombination of atoms — the energy exchange of the system with the environment becomes slower. Consequently, the theoretical model can be applied to such systems (for comparison see Table 1 in43)). The actual equilibrium concentration of the volatile reaction products — CN in the present case - may be reduced by dissociative de-excitation of electronically excited species (cf. also the system C/H2). 

However, the deposition of carbon does not take place on metal surfaces, such as platinum. The reason for this effect is the high catalytic efficiency of pure metals for surface recombination of atoms and metastables, which leads to a decrease of the plasma energy near the surface. Consequently, inequality (2a ) is not fulfilled there (cf.28>). 

Termination is generally a recombination of atoms or radicals in the gas phase, with a third body required to remove excess energy when recombination is between atoms or small radicals. 

Ozone is an inorganic chemical molecule constituted by three oxygen atoms. It is naturally formed in the upper atmosphere from the photolysis of diatomic oxygen and further recombination of atomic and diatomic oxygen according to the following reactions ... 

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