Oxygen photolysis

Monomeric neutral SO4 can be obtained by reaction of SO3 and atomic oxygen photolysis of S03/ozone mixtures also yields monomeric SO4, which can be isolated by inert-gas matrix techniques at low temperatures (15-78 K). Vibration spectroscopy indicates either an open peroxo Cj structure or a closed peroxo C2v structure, the former being preferred by the most recent study, on the basis of agreement between observed and calculated frequencies and reasonable values for the force constants ... 

Nalidixic acid is stable up to five years under reasonable conditions of temperature and humidity. Pawelczyk and Plotkowiakowa(17) subjected sodium nalidixate solutions to accelerated aging, but were unable to identify decomposition products. Detzer and Huber(lS) studied the photolysis and thermolysis of nalidixic acid in the presence of oxygen. Photolysis produced de-carboxylated nalidixic acid, structure A, and a diketone product, structure B, as well as carbon dioxide and ethylamine. 

The photochemical reactions of borazine with oxygen and with water were studied in 1967 The oxygen photolysis reaction produced B-monohydroxy-borazine when borazine was present in excess and diborazinyl when O2 was present in excess. Diborazinyl ether is also produced in the 184.9 run photolysis of borazine with water. This latter reaction is very efficient and diborazinyl ether is often formed in photolysis reactions whenever small amounts of water are present. 

In a solution containing oxygen, photolysis yields a mixture of 6,12-, 1,6-, and 3,6-diones. Nitration by nitrogen dioxide forms 6-nitro-, 1-nitro-, and 3-nitrobenzo[a]pyrene. When benzo [a] pyrene in methanol (1 g/L) was irradiated at 254 nm in a quartz flask for 1 h, the solution turned pale yellow. After 2 h, the solution turned yellow and back to clear after 4 h of irradiation. After 4 h, 99.67% of benzo[a]pyrene was converted to polar compounds. One of these compounds was identified as a methoxylated benzo[a]pyrene (Lu et al, 1977). A carbon dioxide yield of 26.5% was achieved when benzo [a] pyrene adsorbed on silica gel was irradiated with light (A, >290 nm) for 17 h (Freitag et al, 1985). 

The above two reactions account for the layered structure of ozone in the stratosphere. (i) At lower altitudes, the requisite short wavelengths for oxygen photolysis are absent because they are already absorbed by oxygen molecules higher up. Hence, O3 concentration is low at lower altitudes, (ii) At altitudes above the ozone layer, because of the decrease in [O2] due to the general pressure reduction with altitude, the concentration of O2 is low, reducing the efficiency for the termole-cular combination of Reaction 2-168. Hence, O3 concentration is also low. 

The quantum yield varies with pH and with irradiation wavelength, but ranges between 0.2 and 0.5 (108). In the absence of oxygen, photolysis yields Bi2r, and a mixture of methane and ethane [Eq. (103)]. Deuteration... 

Oxidative and UV degradation. Polymers that contain sites of unsaturation, such as polyisoprene and the polybutadienes, are most susceptible to oxygen and ozone oxidation. Figure 14.27 illustrates a typical oxidative degradation of a common elastomer. The figure shows the combined effect of light and oxygen (photolysis) and the action of ozone (ozonolysis). 

In the middle atmosphere, molecular nitrogen is particularly stable since it cannot be photodissociated below the mesopause. On the other hand, the photodissociation of molecular oxygen can occur at altitudes as low as 20 km. Where transport processes can replace the photodissociated molecules, their abundances remain constant, but as photodissociation rates increase at higher altitudes, mixing ratios begin to decline. Oxygen photolysis initiates a series of reactions which determine the chemistry of the oxygen atmosphere these will be the subject of the next section. 

In the upper part of the middle atmosphere, some 0(1D) atoms can also be produced by molecular oxygen photolysis ... 

Note that [M]/[H20] > 100. Hence, OH production is proportional to O3 singlet oxygen photolysis. The second term in Eq. (5.28) contributes a maximum value of about 10 molecules cm to [OH], whereas the first term suggests that [OH] is about 0.03 [HO2]. These values differ considerably from measured values, where [OH] = 0.1 [HO2] — 5-10 molecules cm at the maximum. That is not remarkable because the OH chemistry is much more complex, including other sources and many more sinks (below and Fig. 5.6). 

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