Oxygen atoms, recombination with

The oxygen atoms recombine with oxygen to ozone ... 

Oxygen atoms produced by the ultraviolet dissociation of can take part in several reactions that create and destroy ozone. One set of reactions involving atomic and molecular oxygen is known as the Chapman reactions. The reactions are named after Sydney Chapman (1888-1970) who first proposed them in 1930. In one reaction, an oxygen atom combines with O to form ozone. Alternately, it can recombine with another oxygen atom to produce an oxygen molecule or react with ozone to produce two oxygen molecules. These reactions are summarized as... 

The net conversion of NO to NO2 is limited to the photodissociation of NO2 (NO2 -H hv — NO -1- O). As atomic oxygen rapidly recombines with oxygen to yield ozone, a photostationary state is reached, which governs the concentration of NO, NO2 and O3, the ratio between the two nitrogen oxides being determined by the light intensity. 

Gas phase third-order reactions are rarely encountered in engineering practice. Perhaps the best-known examples of third-order reactions are atomic recombination reactions in the presence of a third body in the gas phase and the reactions of nitric oxide with chlorine and oxygen (2NO T Cl2 -> 2NOC1 2NO + 02 -> 2N02). 

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. 

The mechanism of cytochrome P450 catalysis is probably constant across the system. It is determined by the ability of a high valent formal (FeO) species to carry out one-electron oxidations through the abstraction of hydrogen atoms or electrons. The resultant substrate radical can then recombine with the newly created hydroxyl radical (oxygen rebound) to form the oxidized metabolite. Where a heteroatom is the (rich) source of the electron more than one product is possible. There can be direct recombination to yield the heteroatom oxide or radical relocalization within the... 

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