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Reaction OH (reaction + oh)

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Chemistry	100%

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Rate coefficients for the reactions of OH with n -propanol and iso -propanol between 237 and 376 K

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2010
B. Rajakumar
The rate coefficients for the reaction OH + CH3CH2CH2OH , products (k1) and OH + CH3CH(OH)CH3 , products (k2) were measured by the pulsed-laser photolysis,laser-induced fluorescence technique between 237 and 376 K. Arrhenius expressions for k1 and k2 are as follows: k1 = (6.2 ± 0.8) × 10,12 exp[,(10 ± 30)/T] cm3 molecule,1 s,1, with k1(298 K) = (5.90 ± 0.56) × 10,12 cm3 molecule,1 s,1, and k2 = (3.2 ± 0.3) × 10,12 exp[(150 ± 20)/T] cm3 molecule,1 s,1, with k2(298) = (5.22 ± 0.46) × 10,12 cm3 molecule,1 s,1. The quoted uncertainties are at the 95% confidence level and include estimated systematic errors. The results are compared with those from previous measurements and rate coefficient expressions for atmospheric modeling are recommended. The absorption cross sections for n -propanol and iso -propanol at 184.9 nm were measured to be (8.89 ± 0.44) × 10,19 and (1.90 ± 0.10) × 10,18 cm2 molecule,1, respectively. The atmospheric implications of the degradation of n -propanol and iso -propanol are discussed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 10,24, 2010 [source]

Rate coefficients for the OH + acetaldehyde (CH3CHO) reaction between 204 and 373 K

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 10 2008
Lei Zhu
The rate coefficient, k1, for the gas-phase reaction OH + CH3CHO (acetaldehyde) , products, was measured over the temperature range 204,373 K using pulsed laser photolytic production of OH coupled with its detection via laser-induced fluorescence. The CH3CHO concentration was measured using Fourier transform infrared spectroscopy, UV absorption at 184.9 nm and gas flow rates. The room temperature rate coefficient and Arrhenius expression obtained are k1(296 K) = (1.52 ± 0.15) × 10,11 cm3 molecule,1 s,1 and k1(T) = (5.32 ± 0.55) × 10,12 exp[(315 ± 40)/T] cm3 molecule,1 s,1. The rate coefficient for the reaction OH (, = 1) + CH3CHO, k7(T) (where k7 is the rate coefficient for the overall removal of OH (, = 1)), was determined over the temperature range 204,296 K and is given by k7(T) = (3.5 ± 1.4) × 10,12 exp[(500 ± 90)/T], where k7(296 K) = (1.9 ± 0.6) × 10,11 cm3 molecule,1 s,1. The quoted uncertainties are 2, (95% confidence level). The preexponential term and the room temperature rate coefficient include estimated systematic errors. k7 is slightly larger than k1 over the range of temperatures included in this study. The results from this study were found to be in good agreement with previously reported values of k1(T) for temperatures <298 K. An expression for k1(T), suitable for use in atmospheric models, in the NASA/JPL and IUPAC format, was determined by combining the present results with previously reported values and was found to be k1(298 K) = 1.5 × 10,11 cm3 molecule,1 s,1, f(298 K) = 1.1, E/R = 340 K, and , E/R (or g) = 20 K over the temperature range relevant to the atmosphere. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 635,646, 2008 [source]

Variational transition-state theory study of the atmospheric reaction OH + O3 , HO2 + O2

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2007
Li-Ping Ju
We report variational transition-state theory calculations for the OH + O3, HO2 + O2 reaction based on the recently reported double many-body expansion potential energy surface for ground-state HO4 [Chem Phys Lett 2000, 331, 474]. The barrier height of 1.884 kcal mol,1 is comparable to the value of 1.77,2.0 kcal mol,1 suggested by experimental measurements, both much smaller than the value of 2.16,5.11 kcal mol,1 predicted by previous ab initio calculations. The calculated rate constant shows good agreement with available experimental results and a previous theoretical dynamics prediction, thus implying that the previous ab initio calculations will significantly underestimate the rate constant. Variational and tunneling effects are found to be negligible over the temperature range 100,2000 K. The O1O2 bond is shown to be spectator like during the reactive process, which confirms a previous theoretical dynamics prediction. © 2007 Wiley Periodicals, Inc. 39: 148,153, 2007 [source]

The Reaction of Ozone with the Hydroxide Ion: Mechanistic Considerations Based on Thermokinetic and Quantum Chemical Calculations and the Role of HO4, in Superoxide Dismutation

CHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2010
Gábor Merényi Prof.
Abstract The reaction of OH, with O3 eventually leads to the formation of . OH radicals. In the original mechanistic concept (J. Staehelin, J. Hoigné, Environ. Sci. Technol.1982, 16, 676,681), it was suggested that the first step occurred by O transfer: OH,+O3,HO2,+O2 and that . OH was generated in the subsequent reaction(s) of HO2, with O3 (the peroxone process). This mechanistic concept has now been revised on the basis of thermokinetic and quantum chemical calculations. A one-step O transfer such as that mentioned above would require the release of O2 in its excited singlet state (1O2, O2(1,g)); this state lies 95.5,kJ,mol,1 above the triplet ground state (3O2, O2(3,g,)). The low experimental rate constant of 70,M,1,s,1 is not incompatible with such a reaction. However, according to our calculations, the reaction of OH, with O3 to form an adduct (OH,+O3,HO4,; ,G=3.5,kJ,mol,1) is a much better candidate for the rate-determining step as compared with the significantly more endergonic O transfer (,G=26.7,kJ,mol,1). Hence, we favor this reaction; all the more so as numerous precedents of similar ozone adduct formation are known in the literature. Three potential decay routes of the adduct HO4, have been probed: HO4,,HO2,+1O2 is spin allowed, but markedly endergonic (,G=23.2,kJ,mol,1). HO4,,HO2,+3O2 is spin forbidden (,G=,73.3,kJ,mol,1). The decay into radicals, HO4,,HO2.+O2.,, is spin allowed and less endergonic (,G=14.8,kJ,mol,1) than HO4,,HO2,+1O2. It is thus HO4,,HO2.+O2., by which HO4, decays. It is noted that a large contribution of the reverse of this reaction, HO2.+O2.,,HO4,, followed by HO4,,HO2,+3O2, now explains why the measured rate of the bimolecular decay of HO2. and O2., into HO2,+O2 (k=1×108,M,1,s,1) is below diffusion controlled. Because k for the process HO4,,HO2.+O2., is much larger than k for the reverse of OH,+O3,HO4,, the forward reaction OH,+O3,HO4, is practically irreversible. [source]