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HO2 radicals

R is hydrogen, alkenyl, or alkyne. In remote tropospheric air where NO concentrations ate sometimes quite low, HO2 radicals can react with ozone (HO2 + O3 — HO + 2 O2) and result in net ozone destmction rather than formation. The ambient ozone concentration depends on cloud cover, time of day and year, and geographical location. [Pg.497]

At sufficiently high concentration of iron(iri) and copper(II), the induced oxidation by oxygen is eliminated because all the HO2 radicals are oxidized by steps (55) or (56). In such cases F approaches infinity and Xas becomes equal to 1, i.e. arsenic(III) is oxidized according to equation B. Consequently, iron(II) is reformed at the same rate as it is oxidized. [Pg.541]

The extent of induced oxidation increases with increasing hydrogen ion concentration. This is a consequence of the fact that both iron(II) and iron(III) are present in the solution and compete for HO2 radicals, reactions (52) and (55). The rate of reaction (52) increases as the acidity is increased, whereas that of (55) is independent of hydrogen ion concentration. [Pg.541]

In principle there is a competition for the HO2 radical between peroxydisulphate and hydrogen peroxide [reactions (63) and (86)] however, when the stoichiometry is 1 1 reaction (86) can be neglected. Assuming that the chain length is large, with the usual steady-state approximation, we obtain the following rate equation ... [Pg.557]

From these relations it can be concluded that ksi > k 3 > k, which implies that the concentrations of SO4 and HO2 radicals are relatively large compared to that of OH. It is striking, however, that for kinetic reasons this mechanism does not involve termination steps (78) and (89) which are widely favoured in the chemistry of HO2 and OH radicals... [Pg.557]

It is worth mentioning that an attempt was made by Tsao and Willmarth to determine the acid dissociation constant of HO2. The reaction between hydrogen peroxide and peroxydisulphate was used for the generation of the HO2 radical. However, these experiments, like others where the HO2 radical is studied under steady-state conditions, could yield only a value of acidity constant multiplied by a coefficient consisting of a ratio of kinetic parameters. Unfortunately, in this case there are no independent data for the kinetic coefficient, and the value of cannot be evaluated. Considering the kinetic analogue of the titration curve it can be stated only that ionization of HO2 becomes important in the pH range from 4.5-6.5. The value of acidity constant of HO2 obtained by Czapski and Dorfman is (3.5 + 2.0)x 10 mole.l. . ... [Pg.558]

The HO2 radical formed being a strong reducing agent Eq = —0.13 V ) attacks the peroxydisulphate present according to... [Pg.559]

The sulphate radical formed either reacts directly with H2O2 or, according to the assumption of Tsao and Willmarth °, is converted to OH (step 84) which reacts with hydrogen peroxide, the HO2 radical being reformed, viz. [Pg.559]

According to Bielski and Allen , since the HO2 radical is of amphoteric character, it will be either protonated... [Pg.560]

Induced decomposition of hydrogen peroxide can be interpreted as follows. The HO2 radical formed in reaction (91) reduces OSO4, which will be re-oxidised... [Pg.563]

The OH radical formed in reaction (97) forms a HO2 radical again in reaction (85) thus, without any extra oxidizing agent being present, a considerable amount of hydrogen peroxide is decomposed. [Pg.564]

The C-C and C-H BDEs for ethane are 377.0 and 423.0kJ/mol, respectively, and the H-0 BDE of hydroperoxyl (HO2 ) radical is only 207.5kJ/mol. The large reaction endothermicities for reactions 6.4 and 6.5 highlight the unlikeliness of their occurrence at lower temperatnres. In pyrolytic (heat, but no oxidant) or high fuel/oxidant ratio conditions, the endothermicities indicate that ethane and other alkanes will... [Pg.250]

Simulation of destruction by POC. The description of the POC given here leads us to the idea of "simulating" the cycle, i.e. specifically producing OH or HO2 radicals and allowing them to react with the paint film. To produce the radicals, we made use of the decomposition of water molecules... [Pg.171]

Cooper, P. L. and Abbatt, J. P. D. Heterogeneous interactions of OH and HO2 radicals with surfaces characteristic of atmospheric particulate matter, J. Phys. Chem., 100,2249-2254,1996. [Pg.16]

Gratpanche, F., Ivanov, A., Devolder, P, Gershenzon, Y., and Saw-erysyn, J.-P Uptake coefficients of OH and HO2 radicals on material surfaces of atmospheric interest, 14 International Symposium on Gas Kinetics, Leeds, September, 1996. [Pg.17]

Kanaya, Y., Matsumoto, J., Kato, S., and Akimoto, H. Behavior of OH and HO2 radicals during the Observations at a Remote Island of Okinawa (ORION99) field campaign 2. Comparison between observations and calculations, J. Geophys. Res.-A., 106,24209-24223,2001. [Pg.17]

Even though HO2 radicals are generated by the scavenging effect, they are much less reactive than OH radicals Bielski et al. 1985 Pignatello 1992). [Pg.227]

Using this scheme, we can track the original alkyl radical through the most likely mechanisms for oxidation at low temperatures that lead to chain-branching. Once formed from the parent molecule (R—H), an alkyl radical (R ) can react with molecular oxygen to form an alkene and hydroperoxyl (HO2 ) radical [Equation (2)], via... [Pg.83]

The bisulfite radical then reacts with molecular oxygen to produce sulfur trioxide and the hydroperoxyl (HO2 ) radical ... [Pg.59]

Therefore one pair of ions produces one OH and one HO2 radicals. The total amount of radicals, which are produced in flue gas by electron beam irradiation, is possible to calculate using reported G-values. The main radicals produced initially through direct and ionic decomposition processes are OH, N, HO2, O, and H. [Pg.737]

It should be noted that (R23) is a chain-propagating reaction, converting H atoms to HO2 radicals. However, because HO2 is much less reactive than H, O, and OH radicals, reaction (R23) acts in effect as a chain-terminating step. In addition to the gas-phase chainterminating steps, radicals may be deactivated at the walls of the vessel... [Pg.561]

At lower temperatures and/or higher pressures, formation of the HO2 radical becomes important... [Pg.584]

Both the methyl (CH3) and the peroxide (HO2) radicals are comparably unreactive. The low reactivity of CH3 is part of the explanation that the oxidation characteristics of methane are different from those of higher hydrocarbons. [Pg.587]

The alkyl radical may also dissociate thermally to form an alkene and a smaller alkyl radical. The mechanism that is initiated by these reactions is chain propagating rather than chain branching and for this reason the overall oxidation rate of the fuel decreases. Also there is a change from OH to HO2 as the main chain carrier, and as we have seen, the HO2 radical is much less reactive than OH. The HO2 radical is formed both from alkyl + O2 hydrogen abstraction reactions such as (R69) and from recombination of hydrogen atoms with O2, H + O2 + M HO2 + M (R5). Under lean conditions any hydrogen atoms formed will primarily react with oxygen. At intermediate temperatures the reaction H + O2 O + OH (Rl) is still too slow to compete with (R5). [Pg.597]

This reaction chain requires the presence of sufficient concentrations of NO. At low NO volume mixing ratios, below about 10 pmol/mol (p = pico = 1 O 12 pptv in US units), oxidation of CO leads to ozone destruction since the HO2 radical then reacts mostly with O3 ... [Pg.5]

Thus, O2 " and HO2 radicals behave very differently. While the H02 radical undergoes an H-abstraction [reactions (80)-(83)] and behaves like an ordinary peroxyl radical, the 02 reaction sequence is initiated by an addition reaction [reaction (84), see below]. The H-abstraction reaction (80) is slow (k = 120 dm3 mol"1 s 1). Similar conclusions, revising an earlier report (Schulte-Frohlinde et al. 1986), have been obtained by Hildenbrand and Schulte-Frohlinde (1997) for the reaction of DNA peroxyl radicals with GSH. [Pg.181]

Hydrogen peroxide is an interesting molecule from both structural and chemical point of view. It is chemically the smallest molecule showing internal rotation. It is an important constituent of troposphere and stratosphere, the recombination ofthe two HO2 radicals being the main cause otTLC formation in atmosphere. It is related to acid rain formation by the oxidation of SO2 by H2O2 either in gas phase or in a water droplet [1-4]. Techniques for the detection of H2O2 can be... [Pg.65]

In their system, sufficient nitric oxide (NO) was present to react with the HO2 radical, reforming the HO radical. [Pg.438]


See other pages where HO2 radicals is mentioned: [Pg.497]    [Pg.232]    [Pg.232]    [Pg.560]    [Pg.562]    [Pg.562]    [Pg.562]    [Pg.565]    [Pg.129]    [Pg.252]    [Pg.124]    [Pg.270]    [Pg.10]    [Pg.16]    [Pg.17]    [Pg.81]    [Pg.214]    [Pg.85]    [Pg.92]    [Pg.214]    [Pg.2]    [Pg.11]   
See also in sourсe #XX -- [ Pg.103 ]




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And HO2 radicals

HO2 radical reaction with

HO2 radical, reactions

Reactions of HO2, CH3O2 Radicals

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