Ozone photolysis quantum yield

The quantum yield of ozone decomposition at 334 nm (L2) is 4, indicating that one of the products must be an excited species capable of decomposing 0 further. The primary process of the 0 photolysis at 334 nm occurs according to the reactions ... 

Quantum yields for formaldehyde photolysis have not received the same attention as those for ozone photolysis and are clearly important even in an unpolluted environment. The absorption spectmm is highly structured and more detailed measurements, under atmospheric conditions, are needed. In this work the uncertainty in HCHO measurements was es-... 

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. 

Reactions of Of D) Atoms with H2, 02, N20, H20, CH4, atul Chloro-fluoromethanes. O( D) + H2 (276). No physical quenching was found (791). DeMore (276) has studied the photolysis at 2537 A of mixtures of 03-H2 dissolved in liquid argon at 87 K. The quantum yield of ozone decomposi-... 

The photochemical processes of triatomic molecules have been extensively studied in recent years, particularly those of water, carbon dioxide, nitrous oxide, nitrogen dioxide, ozone, and sulfur dioxide, as they are important minor constituents of the earth s atmosphere. (Probably more than 200 papers on ozone photolysis alone have been published in the last decade.) Carbon dioxide is the major component of the Mars and Venus atmospheres. The primary photofragments produced and their subsequent reactions are well understood for the above-mentioned six triatomic molecules as the photodissociation involves only two bonds to be ruptured and two fragments formed in various electronic states. The photochemical processes of these six molecules are discussed in detail in the following sections. They illustrate how the knowledge of primary products and their subsequent reactions have aided in interpreting the results obtained by the traditional end product analysis and quantum yield measurements. 

Precise determinations of quantum yields in dry ozone photolysis would be of considerable value in clarifying the possible mechanisms. If an energy or photon chain exists, there is no reason why the quantum yield should be limited to about 6. It should be possible to use experimental conditions where it would be much higher. If an energy or photon chain does not exist, the quantum yield should not exceed 4 or, perhaps, 6. It should be emphasized that the most precise work in the ultraviolet yields a maximum quantum yield of 6 and that an error of 2 in this value would be possible. 

Zweiner, C., Weil, L., and Niessner, R., UV- and UV/ozone degradation of triazine herbicides in a pilot plant estimation of UV-photolysis rate constants and quantum yields, Vorm Wasser, 84, 47-60, 1995. 

These reactions would be followed by the above sequence (15), (16), and (17). The quantum yield of ozone disappearance would now be equal to six. It is known further (Table IV) that, at wavelengths above 5900 A., only the ground state 0(3P) atom is formed in the photolysis of ozone and the reaction (17) is incapable of propagating a chain. Thus, it is to be expected that the ozone quantum yield should be 2 at wavelengths > 5900 A. This has now been confirmed experimentally.44 There does not appear to have been any study of the vacuum ultraviolet photolysis of ozone but it should be apparent from the foregoing discussion that reactions of electronically excited O and 02 are involved. 

Table 4 Reported quantum yields for 0(1D) production from ozone photolysis...

Fig-1 Quantum yield for 0(1D) production from ozone photolysis as a function of wavelength [16,19,29,42,43,227-229]... 

The absorption cross sections for O3 at 273 K as recommended by the 2004 JPL/NASA evaluation are given in Table 3 while measured quantum yields (Fig. 1) for ozone photolysis are given in Table 4. In addition, the JPL/NASA evaluation committee has developed an empirical equation for the estimation of the quantum yield for 0( D) as a function of wavelength and temperature (Table 5). 

The absorption cross sections for NO2 and the corresponding quantum yields are given in Table 8 and 9, respectively. The photolysis of NO2 has been investigated intensively over the last 40 years because of its critical role in the formation of ozone in the polluted tropospheric boundary layer [56-63]. The three reactions of Eqs. 33 and 34 form the basis for the photochemical production of ozone. If one considers only these three reactions, then the photo-stationary state (or photochemical steady-state approximation) can be invoked around the oxygen atom as follows ... 

Gurol and Akata [43] studied the kinetics of ozone photolysis following a conceptual model based on possible reaction pathways. They obtained experimentally the primary quantum yield of ozone photolysis at 254 nm (0.48). 

Table 6.6 gives the quantum yields for the ozone photolysis as a function of wavelength [270].) This produces a density of approximately 1010 (a 1A ) molecules cm-3 in the normal atmosphere at altitudes in the vicinity of 50 km [155, 156], Another mechanism that may contribute, particularly in the disturbed atmosphere [157], is... 

Another feature of interest is related to the quantum yields of hydrogen peroxide and of ozone photochemistry as is outlined in Fig. 6-12. Theoretically, the photolysis of 1 mol of H2O2 should produce 2 mol of hydroxyl radicals with a calculated maximum quantum yield of two, according to the definition of presented in Tab. 3-7 = However, the experimental situation is much... 

The photolysis of CCI3F at 213.9 nm and 25 C in the presence of dioxygen [1037,1325a] or ozone gives COCIF and dichlorine as the products, with quantum yields corresponding to 4>(COClF) = 0.90 and 4(Clj) = 0.50-0.63 [1037]. COCIF was also found to be the photooxidation product of CCI3F at 184.9 nm, with a quantum yield near to unity ( 0.96) [88]. A similar reaction occurs when 0( D) atoms combined with CCl 3F [88], the overall reaction being represented by [1624] ... 

Some reaction is found to occur between 0( D) atoms (produced from the photolysis of ozone at 253.7 nm and 25 C) and COCIF, as indicated by the high value of the quantum yield for ozone removal. However, no products were found (although analysis was not made for CO 2 which could be the major product), unlike the COCl 2 0( D) reaction, in which evidence was obtained for the formation of both CO and chlorine oxides [1038]. The rate constant for the reaction of COCIF with 0( D) atoms was estimated to be 2.8 times the value... 

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