OH formation yield

In order to determine the OH formation yields from the reaction of O3 with the cycloalkenes two different sets of experiments were carried out. Firstly, the loss of O3 and the cycloalkene were monitored in experiments where [O3]o and [cycloalkeneJo were in the range 1 to 6 ppm. The results provided values for the stoichiometry of the reactions, A[cycloalkene] / A[03]. In a second series of experiments, sufficient cyclohexane was added to the reaction system in order to scavenge OH radicals formed in the ozone-cycloalkene reactions. In these experiments the loss of cycloalkene, O3 and the yield of cyclohexanone, formed by the reaction of OH with cyclohexane were monitored. In order to determine the yield of cyclohexanone resulting from the reaction of OH with cyclohexane under the reaction conditions employed for the 03/cycloalkene/cyclohexane experiments, a series of experiments was carried out in which the cyclohexane concentrations employed were such that the OH radicals react both with the cycloalkene and cyclohexane. Under these conditions the loss of cyclohexane due to reaction with OH and the formation of cyclohexanone could be determined. The results from these studies showed that A[cyclohexanone] / A[cyclohexane] = 0.26 0.04 for all the alkenes investigated. 

This value can be used in conjunction with the data from experiments where the loss of cycloalkene and yields of cyclohexanone were determined in experiments where cyclohexane was present in high enough concentrations to scavenge all the OH radicals produced in the 03-cycloalkene reactions. The OH formation yields were derived from both the reaction stoichiometries and from the amounts of cyclohexanone detected, and are shown in Table 2. 

Paulson, S.E., Fenske, J.D., Sen, A.D., Callahan, T.W. A novel small-ratio relative-rate technique for measuring OH formation yields from the reactions of O3 with alkenes in the gas phase, and Its application to the reactions of ethene and propene. J. Phys. Chem. A103,2050-2059 (1999) Peiro-Garci a, J., Nebot-Gil, I. Ab initio study on the mechanism of the atmospheric reaction OH -I- O3 —> HO2 + O2. Chem. Phys. Chem. 4, 843-847 (2003a)... 

The formation of OH radicals by the reaction of alkenes and O3 in the polluted atmosphere is very important in atmospheric chemistry of ozone formation described in the next section. The yields of OH radicals under the atmospheric pressure are compiled by the lUPAC subcommittee (Atkinson et al. 2006) and summarized in Table 7.3. These values are those obtained by the batch type experiments with OH scavengers, while Kroll et al. (2001a) investigated pressure dependence (1 00 torr) of the initial OH yields in the reaction of O3 and alkene using a high-pressure flow system coupled with the direct detection of OH by LIF. From this experiment, strong pressure dependence was found for the OH formation yields from alkenes other than ethylene with the OH yields higher than unity at low... 

The gas-phase reaction of N2O5 and naphthalene in an environmental chamber at room temperature resulted in the formation of 1- and 2-nitronaphthalene with approximate yields of 18 and 7.5%, respectively (Pitts et ah, 1985). The reaction of naphthalene with NOx to form nitronaphthalene was reported to occur in urban air from St. Louis, MO (Randahl et ah, 1982). The gas-phase reaction of naphthalene with OH radicals yielded phthalaldehyde, phthalic anhydride, phthalide, 1,4-naphthoquione, cis- and rra/J5-2-formylcinnamaldehyde, and 2,3-epoxy-1,4-naphthoquinone. 

Quantum Yields of Photohydrolysis of some Halogenopyridines at Different pH Values 4>x, Disappearance of Halogenopyridine oH> Formation of Hydroxypyridine... 

Chew, A. A., and R. Atkinson, OH Radical Formation Yields from the Gas-Phase Reactions of 03 with Alkenes and Monoterpenes, J. Geophys. Res., 101, 28649-28653 (1996). 

A more reliable means of providing a reference of -OH in a biological system maybe by means of irradiation with ionizing radiation (von Sonntag et al. 2000). The action of ionizing radiation on an aqueous medium gives rise to OH whose yield/dose relationship (G value) is known (Chap. 2). Apart from this, since biological media are concentrated solutions the formation of the indicator product, e.g., a phenol (ArOH), via the direct effect [expressions (69) and (70)] must in principle be taken into account as well. It can be shown that with k4i [probe]/ k42 [cellular components] above 10 4 the direct effect contributes less than 10%... 

There are clearly several areas of significant uncertainty, including the role of photolysis in both the gas and particle phases and the identities and formation yields of the products of the gas-phase OH radical reactions. 

P0F4 has not been definitively characterized. Both °PoCLt and °PoO(OH)2 yield a white solid when they undergo reaction with aqueous HF. This may be P0F4. The solubility of Po in aqueous HF increases with increasing HF concentration and this behavior has been interpreted in terms of the formation of the PoFe ion. 

Trivalent molybdenum is found in a few simple compounds. The black hydroxide, Mo(OH)3, dissolves in acids -with salt formation, yielding reddish-purple solutions which darken in colour. Upon evaporation crystalline salts are not obtained, but when the solution is taken to dryness a greyish-black residue remains, which can be redissolved in water to a dark grey solution. This may be accounted for by the readiness with which the salts undergo hydrolysis, with formation of the black hydroxide, possibly in the eoUoidal form. The similarity of molybdenum to chromium is seen in the series of complex For indications of basic properties in the trioxide, see p. 137. 

Half are D-sugars (OH on carbon 5 to the right) and half are L-sugars (OH on carbon 5 to the left). A fifth asymmetric carbon atom is produced upon ring formation yielding the a and / anomers of each of the 16 sugars. 

Figure 31. Representative data showing OH formation following 236 nm CO2-HI excitation. The ordinates in (a) and (b) are the Qi,(l) and Qi,(6) LIF signals, respectively, while the abscissa is the delay time. The dashed curve is the response function of the laser system. The solid curves are the calculated best fits, assuming a two-parameter description for the time dependence of OH formation the best least-squares fits yielded (a) t, = 0.9 ps and Tj = 1.9 ps, and (b) x, = 0.7 ps and Xj = 1.1 ps (see Table 4). The points at the top are the residuals between the experimental points and the smooth fit. From Ref. 43 with permission of the Journal of Chemical Physics.

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