Oxygen ozone formation

O2 + A > ( i=180-240 nm) 0 + 0 Second, an oxygen molecule captures one of these oxygen atoms to form an ozone molecule 02+0 03+ Heat The second step occurs twice for each O2 fragmentation, giving the overall balanced process for ozone formation 3 O2 + h V( =l30-240 nm) Heat... 

The extent to which this occurs depends on a number of issues (Finlayson-Pitts and Pitts 1997), including the reactivity of the hydrocarbon that is itself a function of many factors. It has been proposed that the possibility of ozone formation is best described by a reactivity index of incremental hydrocarbon reactivity (Carter and Atkinson 1987, 1989) that combines the rate of formation of O3 with that of the reduction in the concentration of NO. The method has been applied, for example, to oxygenate additives to automobile fuel (Japar et al. 1991), while both anthropogenic compounds and naturally occurring hydrocarbons may be reactive. 

In the present-day atmosphere ozone forms into layers and this was first explained by Chapman who proposed a photolysis mechanism for ozone formation. Chapman s mechanism is a simple steady-state production of ozone and led to the concept of odd oxygen. The odd-oxygen reaction scheme is shown in Table 7.4. 

Reaction 2-2 is actually a three-body process, in that another molecule (Af), usually nitrogen or oxygen, is necessary to carry off the energy released in the newly formed bond. These two reactions then form a mechanism for ozone formation in the atmosphere. They would not be complete without the additional reaction,... 

Washida, N., Y. Mori, and I. Tanaka. Quantum yield of ozone formation from photolysis of the oxygen molecule at 1849 and 1931 A. J. Chem. Phys. 54 1119-1122, 1971. 

Corey and coworkers have shown that trimethylsilyl hydrotrioxide, produced by the low-temperature (—78°C) ozonization of triethylsilane, decomposes at higher temperatures to give singlet oxygen. The formation of singlet oxygen was confirmed by the change in the IR emission at 1278 nm with time ( O2 2). ... 

From thermochemical considerations only, light of wavelength less than 8420 A. could possibly bring about ozone formation from oxygen. However, of the probable mechanisms, the one requiring the least energy is... 

The effects of various added gases on the rate of formation of ozone in a flow system have been studied at 1849 A. with light from a mercury-rare gas low pressure discharge (92). In a 30-mm. diameter cylindrical quartz reaction vessel at a flow rate of 2.0 l./min. at 1-atm. total pressure and 0.25-atm. oxygen pressure, the relative rates of ozone formation were ... 

Wilkinson and Mulliken (105) have pointed out that a direct transition from 32ff to 3IIU is allowed, and have obtained evidence for a weak continuum attributable to 3nu - 32s. They suggested that this may be more important in the decomposition of oxygen above 1750 A. than predissociation of 32u. If this were the case, the quantum yield of ozone formation would have to be quite small at 1849 A. since most of the light would still be absorbed in the transition 32 32 . Although quan-... 

Of the above reactions, only (15) is consistent with the experimental observations. Calculations from collision theory based on the endother-micity of reaction (13) indicate that only one collision in about 104 could yield oxygen atoms. Since the quantum yield of ozone formation has been estimated at 0.03 (91) and as high as 0.14 (18), and since long chains are not possible, this reaction cannot be important. In reaction (14) one mercury atom is removed for each oxygen atom formed. Since 60 or more ozone molecules may be formed for each mercury atom removed, this reaction cannot be important unless mercury is regenerated. The postulated reaction (61)... 

Ozone Formation. Ozone is formed by the same mechanism as discussed in Part II. At constant flow rate and oxygen pressure of 0.25 atm. in a total pressure of 1 atm., the ozone yield was studied in... 

Reactions (1) and (2) essentially convert solar radiant energy into thermal energy. The parameters which determine the rate of ozone formation (UV photon flux, atomic and molecular oxygen number density and the total gas number density) are not constant with altitude and so the ozone concentration and hence Tg varies with altitude. The net result is that Tg increases thoughout the stratosphere until a maximum is reached at the stratopause whence Tg begins to decrease again. 

It has already been mentioned that the excess potential phenomenon occurs also with the oxidation phenomena. Thus it is possible to conyert p-nitrotoluene into p-nitrobenzoic acid at lead-peroxide anodes, while at platinum anodes only the alcohol is formed. It still seems inexplicable how this peculiar action of the anode material takes place. The simplest yet sufficient. explanation is to assume that the anode is capable of influencing catalytically the oxidation process as well as the formation of molecular oxygen. If the first process is accelerated and the second retarded, we obtain the excess potential by which the evolution of oxygen occurs only at a higher potential. Inversely, the oxygen and ozone formation cart be made reversible, and the oxidizing action decreased. 

A chemically based, mass-independent fractionation process was first observed during ozone formation through the gas-phase recombination reaction (Thiemens Heidenreich 1983) O + O2 + M - O3 + M. The product ozone possesses equally enriched heavy-oxygen isotopes I7 IS0. by approximately lOO /oo with respect to the initial oxygen, with a slope value of unity in a three-isotope oxygen plot. This discovery led to the conclusion that a symmetry-dependent reaction can produce meteoritic isotopic anomalies (Thiemens 1999, 2006). Recently, theoretical calculations of Gao Marcus (2001) established the major role of symmetry in isotopolog-specific stabilization of vibrationally excited ozone molecules that give rise to the mass-independent compositions. 

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