Rate constants and the H atom branching ratio of the reactions of the methylidyne CH(X2Π) radical with C2H2, C2H4, C3H4(methylacetylene and allene), C3H6(propene) and C4H8(trans-butene)

2009 ◽  
Vol 11 (4) ◽  
pp. 655-664 ◽  
Author(s):  
Jean-Christophe Loison ◽  
Astrid Bergeat
Keyword(s):  
Rate Constants ◽  
Branching Ratio ◽  
Trans Butene

scholarly journals A new source of methyl glyoxal in the aqueous phase

2015 ◽  
Vol 15 (21) ◽  
pp. 31891-31924
Author(s):  
M. Rodigast ◽  
A. Mutzel ◽  
J. Schindelka ◽  
H. Herrmann
Keyword(s):  
Aqueous Phase ◽  
Rate Constants ◽  
Branching Ratio ◽  
Oxidation Products ◽  
Multiphase System ◽  
Oh Radicals ◽  
Methyl Glyoxal ◽  
Water Ice ◽  
Model Study ◽  
Phase Chemistry

Abstract. Carbonyl compounds are ubiquitous in atmospheric multiphase system participating in gas, particle, and aqueous-phase chemistry. One important compound is methyl ethyl ketone (MEK), as it is detected in significant amounts in the gas phase as well as in cloud water, ice, and rain. Consequently, it can be expected that MEK influences the liquid phase chemistry. Therefore, the oxidation of MEK and the formation of corresponding oxidation products were investigated in the aqueous phase. Several oxidation products were identified from the oxidation with OH radicals, including 2,3-butanedione, hydroxyacetone, and methyl glyoxal. The molar yields were 29.5 % for 2,3-butanedione, 3.0 % for hydroxyacetone, and 9.5 % for methyl glyoxal. Since methyl glyoxal is often related to the formation of organics in the aqueous phase, MEK should be considered for the formation of aqueous secondary organic aerosol (aqSOA). Based on the experimentally obtained data, a reaction mechanism for the formation of methyl glyoxal has been developed and evaluated with a model study. Besides known rate constants, the model contains measured photolysis rate constants for MEK (kp = 5 × 10−5 s−1), 2,3-butanedione (kp = 9 × 10−6 s−1), methyl glyoxal (kp = 3 × 10−5 s−1), and hydroxyacetone (kp = 2 × 10−5 s−1). From the model predictions, a branching ratio of 60/40 for primary/secondary H-atom abstraction at the MEK skeleton was found. This branching ratio reproduces the experiment results very well, especially the methyl glyoxal formation, which showed excellent agreement. Overall, this study demonstrates MEK as a methyl glyoxal precursor compound for the first time.

scholarly journals Ab initio and transition state theory study of the OH + HO2 → H2O + O2(3Σg−)/O2(1Δg) reactions: yield and role of O2(1Δg) in H2O2 decomposition and in combustion of H2

2018 ◽  
Vol 20 (6) ◽  
pp. 4478-4489 ◽  
Author(s):  
M. Monge-Palacios ◽  
S. Mani Sarathy
Keyword(s):  
Transition State ◽  
Ab Initio ◽  
Rate Constants ◽  
Transition State Theory ◽  
Initial Conditions ◽  
Branching Ratio ◽  
State Theory ◽  
H2o2 Decomposition ◽  
P Rate

Rate constants for the reactions OH + HO2 → H2O + O2(3Σg−)/O2(1Δg) have been calculated. The branching ratio to O2(1Δg) is small, and thus particular initial conditions are needed for O2(1Δg) to play a role in combustion.

scholarly journals Photolysis and oxidation by OH radicals of two carbonyl nitrates: 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone

2019 ◽  
Author(s):  
Bénédicte Picquet-Varrault ◽  
Ricardo Suarez-Bertoa ◽  
Marius Duncianu ◽  
Mathieu Cazaunau ◽  
Edouard Pangui ◽  
...  
Keyword(s):  
Cross Sections ◽  
Rate Constants ◽  
Branching Ratio ◽  
Quantum Yields ◽  
Organic Nitrates ◽  
Oh Radicals ◽  
Important Species ◽  
Photolysis Rates ◽  
Photolysis Frequencies ◽  
First Time

Abstract. Multifunctional organic nitrates, including carbonyl nitrates, are important species formed in NOx rich atmospheres by the degradation of VOCs. These compounds have been shown to play a key role in the transport of reactive nitrogen and consequently in the ozone budget, but also to be important components of the total organic aerosol. However, very little is known about their reactivity in both gas and condensed phases. Following a previous study we published on the gas-phase reactivity of β-nitrooxy ketones, the photolysis and the reaction with OH radicals of 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone, respectively a β-nitrooxy ketone and a γ-nitrooxy ketone, were investigated for the first time in simulation chambers. Ambient photolysis frequencies calculated for 40° latitude North were found to be (4.2 ± 0.6) × 10−5 s−1 and (2.2 ± 0.7) × 10−5 s−1 for 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone, respectively. These results demonstrate that photolysis is a very efficient sink for these compounds with atmospheric lifetimes of few hours. It was also concluded that, similarly to α-nitrooxy ketones, β-nitrooxy ketones have enhanced UV absorption cross sections and quantum yields equal or close to unity. γ-nitrooxy ketones have been shown to have lower enhancement of cross sections which can easily be explained by the increasing distance between the two chromophore groups. Thanks to a products study, branching ratio between the two possible photodissociation pathways are also proposed. Rate constants for the reaction with OH radicals were found to be (2.9 ± 1.0) × 10−12 cm3 molecule−1 s−1 and (3.3 ± 0.9) × 10−12 cm3 molecule−1 s−1, respectively. These experimental data are in good agreement with rate constants estimated by the SAR of Kwok and Atkinson (1995) when using the parametrization proposed by Suarez-Bertoa et al. (2012) for carbonyl nitrates. Comparison with photolysis rates suggests that OH-initiated oxidation of carbonyl nitrates is a less efficient sink that photodissociation but is not negligible in polluted area.

scholarly journals Photolysis and oxidation by OH radicals of two carbonyl nitrates: 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone

2020 ◽  
Vol 20 (1) ◽  
pp. 487-498 ◽  
Author(s):  
Bénédicte Picquet-Varrault ◽  
Ricardo Suarez-Bertoa ◽  
Marius Duncianu ◽  
Mathieu Cazaunau ◽  
Edouard Pangui ◽  
...  
Keyword(s):  
Cross Sections ◽  
Rate Constants ◽  
Branching Ratio ◽  
Quantum Yields ◽  
Organic Nitrates ◽  
Oh Radicals ◽  
Experimental Conditions ◽  
Important Species ◽  
Photolysis Rates ◽  
Photolysis Frequencies

Abstract. Multifunctional organic nitrates, including carbonyl nitrates, are important species formed in NOx-rich atmospheres by the degradation of volatile organic compounds (VOCs). These compounds have been shown to play a key role in the transport of reactive nitrogen and, consequently, in the ozone budget; they are also known to be important components of the total organic aerosol. However, very little is known about their reactivity in both the gas and condensed phases. Following a previous study that we published on the gas-phase reactivity of α-nitrooxy ketones, the photolysis and reaction with OH radicals of 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone (which are a β-nitrooxy ketone and γ-nitrooxy ketone, respectively) were investigated for the first time in simulation chambers. The photolysis frequencies were directly measured in the CESAM chamber, which is equipped with a very realistic irradiation system. The jnitrate/jNO2 ratios were found to be (5.9±0.9)×10-3 for 4-nitrooxy-2-butanone and (3.2±0.9)×10-3 for 5-nitrooxy-2-pentanone under our experimental conditions. From these results, it was estimated that ambient photolysis frequencies calculated for typical tropospheric irradiation conditions corresponding to the 1 July at noon at 40∘ N (overhead ozone column of 300 and albedo of 0.1) are (6.1±0.9)×10-5 s−1 and (3.3±0.9)×10-5 s−1 for 4-nitrooxy-2-butanone and 5-nitrooxy-2-pentanone, respectively. These results demonstrate that photolysis is a very efficient sink for these compounds with atmospheric lifetimes of few hours. They also suggest that, similarly to α-nitrooxy ketones, β-nitrooxy ketones have enhanced UV absorption cross sections and quantum yields equal to or close to unity and that γ-nitrooxy ketones have a lower enhancement of cross sections, which can easily be explained by the larger distance between the two chromophore groups. Thanks to a product study, the branching ratio between the two possible photodissociation pathways is also proposed. Rate constants for the reaction with OH radicals were found to be (2.9±1.0)×10-12 and (3.3±0.9)×10-12 cm3 molecule−1 s−1, respectively. These experimental data are in good agreement with rate constants estimated by the structure–activity relationship (SAR) of Kwok and Atkinson (1995) when using the parametrization proposed by Suarez-Bertoa et al. (2012) for carbonyl nitrates. Comparison with photolysis rates suggests that the OH-initiated oxidation of carbonyl nitrates is a less efficient sink than photodissociation but is not negligible in polluted areas.

scholarly journals A new source of methylglyoxal in the aqueous phase

2016 ◽  
Vol 16 (4) ◽  
pp. 2689-2702 ◽  
Author(s):  
Maria Rodigast ◽  
Anke Mutzel ◽  
Janine Schindelka ◽  
Hartmut Herrmann
Keyword(s):  
Aqueous Phase ◽  
Rate Constants ◽  
Branching Ratio ◽  
Oxidation Products ◽  
Multiphase System ◽  
Oh Radicals ◽  
Water Ice ◽  
Model Study ◽  
Phase Chemistry ◽  
First Time

Abstract. Carbonyl compounds are ubiquitous in atmospheric multiphase system participating in gas, particle, and aqueous-phase chemistry. One important compound is methyl ethyl ketone (MEK), as it is detected in significant amounts in the gas phase as well as in cloud water, ice, and rain. Consequently, it can be expected that MEK influences the liquid-phase chemistry. Therefore, the oxidation of MEK and the formation of corresponding oxidation products were investigated in the aqueous phase. Several oxidation products were identified from the oxidation with OH radicals, including 2,3-butanedione, hydroxyacetone, and methylglyoxal. The molar yields were 29.5 % for 2,3-butanedione, 3.0 % for hydroxyacetone, and 9.5 % for methylglyoxal. Since methylglyoxal is often related to the formation of organics in the aqueous phase, MEK should be considered for the formation of aqueous secondary organic aerosol (aqSOA). Based on the experimentally obtained data, a reaction mechanism for the formation of methylglyoxal has been developed and evaluated with a model study. Besides known rate constants, the model contains measured photolysis rate constants for MEK (kp  =  5  ×  10−5 s−1), 2,3-butanedione (kp  =  9  ×  10−6 s−1), methylglyoxal (kp  =  3  ×  10−5 s−1), and hydroxyacetone (kp  =  2  ×  10−5 s−1). From the model predictions, a branching ratio of 60 /40 for primary/secondary H-atom abstraction at the MEK skeleton was found. This branching ratio reproduces the experiment results very well, especially the methylglyoxal formation, which showed excellent agreement. Overall, this study demonstrates MEK as a methylglyoxal precursor compound for the first time.

Absolute rate constants, reactive cross-sections and isotopic branching ratio for the reaction of O(1D) with HD

1995 ◽  
Vol 236 (3) ◽  
pp. 343-349 ◽  
Author(s):  
T. Laurent ◽  
P.D. Naik ◽  
H.-R. Volpp ◽  
J. Wolfrum ◽  
T. Arusi-Parpar ◽  
...  
Keyword(s):  
Cross Sections ◽  
Rate Constants ◽  
Branching Ratio ◽  
Absolute Rate
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