Nitrogen dioxide quantum yield

Data have been presented on the kinetics of nitration of acetanilide in mixtures of nitric and sulfuric acids.29 A review discusses the several mechanisms operative in the nitration of phenol including /> / -sclective nitrosation-oxidation and mechanisms involving phenoxy radical-nitrogen dioxide reaction yielding a 55 45 ortho para nitration ratio.30 The kinetics of mononitration of biphenyl-2-carboxylic acid have been investigated in several solvents. The maximum ortho para product ratio of 8.4 is observed in tetrachloromethane.31 Nitration products were not formed in the presence of dioxane.31,32 Quantum-chemical AMI calculations were performed and the predominant formation of the ortho-nitro product is accounted for by stabilization of the cr-complex by the carboxyl group.33... 

Irradiation of mixtures of an olefin with nitric oxide and nitrogen dioxide in air shows that the nitrogen dioxide rises in concentration before it is eventually consumed by reaction. Since it is the photodissociation of the nitrogen dioxide that initiates the reaction, it would appear that a negative quantum yield results. More likely, the nitrogen dioxide is being formed by secondary reactions more rapidly than it is being photodissociated. 

Titanium dioxide suspended in an aqueous solution and irradiated with UV light X = 365 nm) converted benzene to carbon dioxide at a significant rate (Matthews, 1986). Irradiation of benzene in an aqueous solution yields mucondialdehyde. Photolysis of benzene vapor at 1849-2000 A yields ethylene, hydrogen, methane, ethane, toluene, and a polymer resembling cuprene. Other photolysis products reported under different conditions include fulvene, acetylene, substituted trienes (Howard, 1990), phenol, 2-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, 2,6-dinitro-phenol, nitrobenzene, formic acid, and peroxyacetyl nitrate (Calvert and Pitts, 1966). Under atmospheric conditions, the gas-phase reaction with OH radicals and nitrogen oxides resulted in the formation of phenol and nitrobenzene (Atkinson, 1990). Schwarz and Wasik (1976) reported a fluorescence quantum yield of 5.3 x 10" for benzene in water. 

The halogenation of alkanes in the presence of sulphur dioxide yields alkanesulphonyl chlorides (5.79), and these are made in large quantities for conversion to metal alkanesulphonates (used as emulsifiers in polymerizations) or to nitrogen-containing derivatives. The sulphur dioxide acts by trapping the alkyl radical it does not terminate the chain mechanism, and so quantum yields can be very high (—2000). 

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. 

Nitrogen dioxide is one of a few simple molecules in which the primary quantum yield near the dissociation limit (3980 A) has been measured nearly continuously as a function of incident wavelength. The energetics of photodissociation is given in Table VI- 5. The thcrmochcmical threshold at O K for the reaction, N02 - NO + O( P), corresponds to the incident wavelength 3978 A, which nearly coincides with the wavelength 3979 1 A below which... 

Figure 9.6 Electronic spectrum of nitrogen dioxide and ranges of its different photochemical behaviour quantum yield of N02 photodissociation between 300 and 420nm [61...

Quantum Yields. In order to understand these data, it was necessary to obtain the absorption coefficients for the different gaseous substances nitrogen dioxide, nitrogen tetroxide, and nitrogen pentoxide. The oxygen is transparent. The following formula... 

Fig. 29.—Quantum yield at 3,130 A as a function of the light absorbed by nitrogen dioxide. The large circles represent less accurate measurements in the absence of nitrogen pentoxide.

In Fig. 30 it is seen that the effect with carbon dioxide is nearly proportional to the pressure. The reduction in quantum yield is due to the removal by collision of the excess energy of the excited nitrogen dioxide molecules before they can collide with other molecules of nitrogen dioxide and effect a chemical reaction. The energy is removed in the form of extra energy given to the colliding molecules, and thus converted into heat. 

Fig. 30.—Effect of carbon dioxide in reducing the quantum yield < N2°6 (corrected for screening by nitrogen tetroxide) A—4,050, O—3660, 0-3,130 A.

Nitrogen dioxide Nitrate Nitrite Ozone Photochemistry Quantum yield Rate law... 

The quantum yield of reaction 17 varies with the irradiation wavelength, from about 0.07 near 300 nm to 0.025 at 355 nm down to 0.015 at 371 nm [35,40]. Differently from nitrate, nitrite is a source but also a sink for the hydroxyl radical, the latter reaction yielding nitrogen dioxide [35,37-40,43] ... 

Such information can be found in the work of Jaffe and Klein on the photolysis of NO2 in the presence of SO2. They measured the quantum yield of nitrogen dioxide decomposition by in situ NO2 absorptiometry. In the absence of SOj the quantum yield is 2, since each atom of oxygen formed in the primary photolytic process can react with another molecule of NO2... 

Reduction in the quantum yield for the formation of methane resulting from the addition of inert foreign gases such as helium, neon, argon, nitrogen and carbon dioxide supports this suggestion of a hot radical mechanism, as does the observation by Harris and Willard that methane formation is enhanced at short wavelengths (1849 A). Souffle et have also proposed some ethane formation from the reaction of hot radicals by... 

The photodecomposition of HN03 in the 200-300 nm wavelength region has been studied by Johnston et al. (1974). In the presence of excess CO and 02 to scavenge OH radicals so as to prevent their reaction with HNOj, nitrogen dioxide is formed with a quantum yield of unity. This suggests that the principal primary photodissociation process is H N03 — OH + N02. It represents a reversal of the recombination reaction between OH and N02 discussed earlier. 

Fig. 2-16. Absorption spectrum and 0(3P) quantum yields for nitrogen dioxide. Absorption cross sections adapted from Bass el al. (1976), quantum yields from the authors listed. Threshold wavelengths for the formation of 0(3P) and O( D) are indicated.

Obenauf et al. [271] have measured the quantum yield of fluorescence per molecule of target gas consumed in the reaction of barium vapour with nitrogen dioxide and nitrous oxide, obtaining values of 0.20—0.27 for the stronger fluorescence from the nitrous oxide reaction, and 0.015 0.003 for the nitrogen dioxide reaction. Using the values for total reaction cross-section reported by Jonah et al. [270], Obenauf et al. [271] estimate the cross-sections for the chemiluminescent reactions to be < 6—7 for the nitrous oxide reaction and about 2—3 for the nitrogen dioxide reaction. 

The Fixation of Carbon Dioxide and Nitrogen.—As reduced carbon compounds are convenient fuels, the possibility of achieving the reductive fixation of COa in vitro is appealing, if remote. There are very few data on photochemical reactions involving carbon dioxide, for it has no low-lying excited states and has not historically been of much interest to the photochemist. However, what appears to be the first example of photofixation of COa in a non-biological system has been briefly reported.18 Photoirradiation (with a high-pressure mercury lamp) of phenanthrene in the presence of an amine and C02 in a polar solvent (MeaSO or HCONMea) yielded 9,10-dihydrophenanthrene-9-carboxylic acid, in unspecified quantum yield. The mechanism appears to involve formation of COaT by electron transfer from the photoexcited amine, followed by attack of COaT on position 9 of phenanthrene. Similar reductive carboxylation of anthracene, pyrene, naphthalene, and biphenyl was observed. 

Chu, L. and C. Anastasio (2003) Quantum yields of hydroxyl radical and nitrogen dioxide from the photolysis of nitrate on ice. Journal of Physical Chemistry A, 107, 9594-9602 Chyba, C. and C. Sagan (1992) Endogenous production, exogenous delivery and impact-shock synthesis of organic molecules An inventory for the origins of life. Nature 355, 125-132 doi 10.1038/355125a0... 

The formation of oxygen atom 0( P) in the photolysis of nitrogen dioxide (NO2) is the fundamental reaction that causes direct production of O3 in the troposphere. In this section, absorption spectrum and 0( P) production quantum yields relevant to the tropospheric photochemistry are described. 

Ultraviolet Radiation k(nm) Absorption, cut-off Quantum yields (mol/Einstein) (in air) at A = 254 Acetic acid formation Carbon dioxide formation Carbon monoxide fomiation Methane fomiation Chain scission Crosslinking 240 0.01 0.0065 0.0060 0.0038 0.05 (in air), 0.066 (in nitrogen) 0.0025 (in air), 0.047 (in nitrogen) 142 143... 

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