scholarly journals Direct measurements of OH and other product yields from the HO<sub>2</sub> + CH<sub>3</sub>C(O)O<sub>2</sub> reaction

2015 ◽  
Vol 15 (20) ◽  
pp. 28815-28866
Author(s):  
F. A. F. Winiberg ◽  
T. J. Dillon ◽  
S. C. Orr ◽  
C. B. M Groß ◽  
I. Bejan ◽  
...  
Keyword(s):  
Rate Coefficient ◽  
Measurement Model ◽  
Branching Ratios ◽  
Rate Coefficients ◽  
Secondary Products ◽  
Title Reaction ◽  
Direct Measurements ◽  
Series Of Experiments ◽  
First Time ◽  
Good Agreement

Abstract. The reaction CH3C(O)O2 + HO2 &amp;rightarrow; CH3C(O)OOH + O2 (Reaction R5a), CH3C(O)OH + O3 (Reaction R5b), CH3 + CO2 + OH + O2 (Reaction R5c) was studied in a series of experiments conducted at 1000 mbar and (293 ± 2) K in the HIRAC simulation chamber. For the first time, products, (CH3C(O)OOH, CH3C(O)OH, O3 and OH) from all three branching pathways of the reaction have been detected directly and simultaneously. Measurements of radical precursors (CH3OH, CH3CHO), HO2 and some secondary products HCHO and HCOOH further constrained the system. Fitting a comprehensive model to the experimental data, obtained over a range of conditions, determined the branching ratios α(R5a) = 0.37 ± 0.10, α(R5b) = 0.12 ± 0.04 and α(R5c) = 0.51 ± 0.12 (errors at 2σ level). Improved measurement/model agreement was achieved using k(R5) = (2.4 ± 0.4) × 10-11 cm3 molecule-1 s-1, which is within the large uncertainty of the current IUPAC and JPL recommended rate coefficients for the title reaction. The rate coefficient and branching ratios are in good agreement with a recent study performed by Groß et al. (2014b); taken together, these two studies show that the rate of OH regeneration through Reaction (R5) is more rapid than previously thought. GEOS-Chem has been used to assess the implications of the revised rate coefficients and branching ratios; the modelling shows an enhancement of up to 5 % in OH concentrations in tropical rainforest areas and increases of up to 10 % at altitudes of 6–8 km above the equator, compared to calculations based on the IUPAC recommended rate coefficient and yield. The enhanced rate of acetylperoxy consumption significantly reduces PAN in remote regions (up to 30 %) with commensurate reductions in background NOx.

scholarly journals Direct measurements of OH and other product yields from the HO<sub>2</sub>  + CH<sub>3</sub>C(O)O<sub>2</sub> reaction

2016 ◽  
Vol 16 (6) ◽  
pp. 4023-4042 ◽  
Author(s):  
Frank A. F. Winiberg ◽  
Terry J. Dillon ◽  
Stephanie C. Orr ◽  
Christoph B. M Groß ◽  
Iustinian Bejan ◽  
...  
Keyword(s):  
Rate Coefficient ◽  
Measurement Model ◽  
Branching Ratios ◽  
Rate Coefficients ◽  
Secondary Products ◽  
Title Reaction ◽  
Direct Measurements ◽  
Series Of Experiments ◽  
First Time ◽  
Good Agreement

Abstract. The reaction CH3C(O)O2 + HO2  →  CH3C(O)OOH + O2 (Reaction R5a), CH3C(O)OH + O3 (Reaction R5b), CH3 + CO2 + OH + O2 (Reaction R5c) was studied in a series of experiments conducted at 1000 mbar and (293 ± 2) K in the HIRAC simulation chamber. For the first time, products, (CH3C(O)OOH, CH3C(O)OH, O3 and OH) from all three branching pathways of the reaction have been detected directly and simultaneously. Measurements of radical precursors (CH3OH, CH3CHO), HO2 and some secondary products HCHO and HCOOH further constrained the system. Fitting a comprehensive model to the experimental data, obtained over a range of conditions, determined the branching ratios α(R5a)  =  0.37 ± 0.10, α(R5b) =  0.12 ± 0.04 and α(R5c) =  0.51 ± 0.12 (errors at 2σ level). Improved measurement/model agreement was achieved using k(R5)  =  (2.4 ± 0.4)  ×  10−11 cm3 molecule−1 s−1, which is within the large uncertainty of the current IUPAC and JPL recommended rate coefficients for the title reaction. The rate coefficient and branching ratios are in good agreement with a recent study performed by Groß et al. (2014b); taken together, these two studies show that the rate of OH regeneration through Reaction (R5) is more rapid than previously thought. GEOS-Chem has been used to assess the implications of the revised rate coefficients and branching ratios; the modelling shows an enhancement of up to 5 % in OH concentrations in tropical rainforest areas and increases of up to 10 % at altitudes of 6–8 km above the equator, compared to calculations based on the IUPAC recommended rate coefficient and yield. The enhanced rate of acetylperoxy consumption significantly reduces PAN in remote regions (up to 30 %) with commensurate reductions in background NOx.

Dissociative electron recombination of NH2CHOH+ and implications for interstellar formamide abundance

2019 ◽  
Vol 490 (1) ◽  
pp. 1325-1331 ◽  
Author(s):  
M A Ayouz ◽  
C H Yuen ◽  
N Balucani ◽  
C Ceccarelli ◽  
I F Schneider ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Branching Ratios ◽  
Rate Coefficients ◽  
Electron Recombination ◽  
Complex Species ◽  
Star Forming ◽  
Star Forming Regions ◽  
Global Rate ◽  
Cometary Material ◽  
Good Agreement

ABSTRACT Formamide is a potentially important molecule in the context of pre-biotic chemistry, since reactions involving it can lead to precursors of genetic and metabolic molecules. Being abundant in cometary material and in star-forming regions, the formation and destruction routes of interstellar formamide have been the focus of several studies. In this work, we focus on the electron recombination of protonated formamide, an important step of its destruction routes, by performing rigorous ab initio calculations of this process. We found that our values are in good agreement with previous qualitative estimates of the global rate coefficients. On the contrary, we propose a substantial revision of the products and branching ratios. Finally, we justify and emphasize the importance of carrying out similar theoretical calculations on the largest possible number of complex species of astrochemical interest.

scholarly journals The atmospheric chemistry of sulphuryl fluoride, SO<sub>2</sub>F<sub>2</sub>

2008 ◽  
Vol 8 (6) ◽  
pp. 1547-1557 ◽  
Author(s):  
T. J. Dillon ◽  
A. Horowitz ◽  
J. N. Crowley
Keyword(s):  
Atmospheric Chemistry ◽  
Rate Coefficient ◽  
Relative Rate ◽  
Significant Loss ◽  
Rate Coefficients ◽  
Atmospheric Species ◽  
Upper Limits ◽  
Wall Flow ◽  
Temperature Rate ◽  
Good Agreement

Abstract. The atmospheric chemistry of sulphuryl fluoride, SO2F2, was investigated in a series of laboratory studies. A competitive rate method, using pulsed laser photolysis (PLP) to generate O(1D) coupled to detection of OH by laser induced fluorescence (LIF), was used to determine the overall rate coefficient for the reaction O(1D) + SO2F2 → products (R1) of k1 (220–300 K) = (1.3 ± 0.2) × 10−10 cm3 molecule−1 s−1. Monitoring the O(3P) product (R1a) enabled the contribution (α) of the physical quenching process (in which SO2F2 is not consumed) to be determined as α (225–296 K)=(0.55 ± 0.04). Separate, relative rate measurements at 298 K provided a rate coefficient for reactive loss of O(1D), k1b, of (5.8 ± 0.8) × 10−11 cm3 molecule−1 s−1 in good agreement with the value calculated from (1−α) × k1=(5.9 ± 1.0) × 10−11 cm3 molecule−1 s−1. Upper limits for the rate coefficients for reaction of SO2F2 with OH (R2, using PLP-LIF), and with O3 (R3, static reactor) were determined as k2 (294 K)<1 × 10−15 cm3 molecule−1 s−1 and k3 (294 K)<1 × 10−23 cm3 molecule−1 s−1. In experiments using the wetted-wall flow tube technique, no loss of SO2F2 onto aqueous surfaces was observed, allowing an upper limit for the uptake coefficient of γ(pH 2–12)<1 × 10−7 to be determined. These results indicate that SO2F2 has no significant loss processes in the troposphere, and a very long stratospheric lifetime. Integrated band intensities for SO2F2 infrared absorption features between 6 and 19 μm were obtained, and indicate a significant global warming potential for this molecule. In the course of this work, ambient temperature rate coefficients for the reactions O(1D) with several important atmospheric species were determined. The results (in units of 10−10 cm3 molecule−1 s−1, k(O1D + N2)=(0.33 ± 0.06); k(O1D + N2O)=(1.47 ± 0.2) and k(O1D + H2O)=(1.94 ± 0.5) were in good agreement with other recent determinations.

scholarly journals A self-consistent, multivariate method for the determination of gas-phase rate coefficients, applied to reactions of atmospheric VOCs and the hydroxyl radical

2018 ◽  
Vol 18 (6) ◽  
pp. 4039-4054 ◽  
Author(s):  
Jacob T. Shaw ◽  
Richard T. Lidster ◽  
Danny R. Cryer ◽  
Noelia Ramirez ◽  
Fiona C. Whiting ◽  
...  
Keyword(s):  
Gas Phase ◽  
Atmospheric Chemistry ◽  
Rate Coefficient ◽  
Relative Rate ◽  
Ambient Air ◽  
Rate Coefficients ◽  
Oxidation Reactions ◽  
Simultaneous Study ◽  
The University ◽  
Good Agreement

Abstract. Gas-phase rate coefficients are fundamental to understanding atmospheric chemistry, yet experimental data are not available for the oxidation reactions of many of the thousands of volatile organic compounds (VOCs) observed in the troposphere. Here, a new experimental method is reported for the simultaneous study of reactions between multiple different VOCs and OH, the most important daytime atmospheric radical oxidant. This technique is based upon established relative rate concepts but has the advantage of a much higher throughput of target VOCs. By evaluating multiple VOCs in each experiment, and through measurement of the depletion in each VOC after reaction with OH, the OH + VOC reaction rate coefficients can be derived. Results from experiments conducted under controlled laboratory conditions were in good agreement with the available literature for the reaction of 19 VOCs, prepared in synthetic gas mixtures, with OH. This approach was used to determine a rate coefficient for the reaction of OH with 2,3-dimethylpent-1-ene for the first time; k =  5.7 (±0.3)  ×  10−11 cm3 molecule−1 s−1. In addition, a further seven VOCs had only two, or fewer, individual OH rate coefficient measurements available in the literature. The results from this work were in good agreement with those measurements. A similar dataset, at an elevated temperature of 323 (±10) K, was used to determine new OH rate coefficients for 12 aromatic, 5 alkane, 5 alkene and 3 monoterpene VOC + OH reactions. In OH relative reactivity experiments that used ambient air at the University of York, a large number of different VOCs were observed, of which 23 were positively identified. Due to difficulties with detection limits and fully resolving peaks, only 19 OH rate coefficients were derived from these ambient air samples, including 10 reactions for which data were previously unavailable at the elevated reaction temperature of T =  323 (±10) K.

scholarly journals A self-consistent, multi-variate method for the determination of gas phase rate coefficients, applied to reactions of atmospheric VOCs and the hydroxyl radical

2017 ◽  
Author(s):  
Jacob T. Shaw ◽  
Richard T. Lidster ◽  
Danny R. Cryer ◽  
Noelia Ramirez ◽  
Graham A. Boustead ◽  
...  
Keyword(s):  
Gas Phase ◽  
Atmospheric Chemistry ◽  
Rate Coefficient ◽  
Relative Rate ◽  
Ambient Air ◽  
Rate Coefficients ◽  
Oxidation Reactions ◽  
Oh Reactions ◽  
Simultaneous Study ◽  
Good Agreement

Abstract. Gas-phase rate coefficients are fundamental to understanding atmospheric chemistry, yet experimental data are not available for the oxidation reactions of many of the thousands of volatile organic compounds (VOCs) observed in the troposphere. Here a new experimental method is reported for the simultaneous study of reactions between multiple different VOCs and OH, the most important daytime atmospheric radical oxidant. This technique is based upon established relative rate concepts but has the advantage of a much higher throughput of target VOCs. By evaluating multiple VOCs in each experiment, and through measurement of the depletion in each VOC after reaction with OH, the OH + VOC reaction rate coefficients can be derived. Results from experiments conducted under controlled laboratory conditions were in good agreement with the available literature for the reaction of nineteen VOCs, prepared in synthetic gas mixtures, with OH. This approach was used to determine a rate coefficient for the reaction of OH with 2,3-dimethylpent-1-ene for the first time; k = 5.7 (&amp;pm;0.3) × 10–11–cm3 molecule−1 s−1. In addition, a further seven VOCs had only two, or fewer, individual OH rate coefficient measurements available in the literature. The results from this work were in good agreement with those measurements. A similar dataset, at an elevated temperature of 323 (±10) K, was used to determine new OH rate coefficients for twelve aromatic, five alkane, five alkene and three monoterpene VOC + OH reactions. In OH relative reactivity experiments that used ambient air at the University of York, a large number of different VOCs were observed, of which 23 were positively identified. 19 OH rate coefficients were derived from these ambient air samples, including ten reactions for which data was previously unavailable at the elevated reaction temperature of T = 323 (±10) K.

Rate coefficients and product branching ratios for (E)-2-butenal + H reactions

2020 ◽  
Vol 22 (25) ◽  
pp. 14246-14254
Author(s):  
Maiara Oliveira Passos ◽  
Igor Araujo Lins ◽  
Tiago Vinicius Alves
Keyword(s):  
Rate Constants ◽  
Hydrogen Abstraction ◽  
Branching Ratios ◽  
Rate Coefficients ◽  
Variational Theory ◽  
Hydrogen Atoms ◽  
Small Curvature ◽  
Thermal Rate Constants ◽  
First Time ◽  
Product Branching

Thermal rate constants for the hydrogen abstraction reactions of (E)-2-butenal by hydrogen atoms were calculated, for the first time, using the multipath canonical variational theory with small-curvature tunneling (MP-CVT/SCT).

Modified theory of f-f transition intensities and crystal field for systems with anomalously strong configuration interaction

Open Physics ◽  
2008 ◽  
Vol 6 (3) ◽  
Author(s):  
Elena Dunina ◽  
Alexey Kornienko ◽  
Liudmila Fomicheva
Keyword(s):  
Crystal Field ◽  
Configuration Interaction ◽  
Branching Ratios ◽  
The Other ◽  
Stark Splitting ◽  
Satisfactory Description ◽  
First Time ◽  
Modified Theory ◽  
Absorption Transitions ◽  
Good Agreement

AbstractA new theory explaining the intensity of f-f transitions and the crystal field using an approximation of a strong configuration interaction is proposed. The theory enables the anomalous influence of excited configurations with charge transfer on some multiplets of the f shell to be taken into account. With the help of this theory, a satisfactory description of the absorption transitions and luminescence branching ratios from 1 D 2 and 3 P 0 multiplets for the Pr3+ ion in double molybdates has been achieved for the first time. For further validation the theory, was used to provide a description of Stark splitting of Pr3+ — multiplets in elpasolites and determine the covalence parameters; these parameters were found to be in good agreement with values obtained by the other methods.

scholarly journals Reaction between CH<sub>3</sub>C(O)OOH (peracetic acid) and OH in the gas phase: a combined experimental and theoretical study of the kinetics and mechanism

2020 ◽  
Vol 20 (21) ◽  
pp. 13541-13555
Author(s):  
Matias Berasategui ◽  
Damien Amedro ◽  
Luc Vereecken ◽  
Jos Lelieveld ◽  
John N. Crowley
Keyword(s):  
Gas Phase ◽  
Peracetic Acid ◽  
Theoretical Study ◽  
Rate Coefficient ◽  
Theoretical Calculations ◽  
Title Reaction ◽  
Upper Troposphere ◽  
Reaction Proceeds ◽  
Kinetics Of ◽  
Good Agreement

Abstract. Peracetic acid (CH3C(O)OOH) is one of the most abundant organic peroxides in the atmosphere; yet the kinetics of its reaction with OH, believed to be the major sink, have only been studied once experimentally. In this work we combine a pulsed-laser photolysis kinetic study of the title reaction with theoretical calculations of the rate coefficient and mechanism. We demonstrate that the rate coefficient is orders of magnitude lower than previously determined, with an experimentally derived upper limit of 4×10-14 cm3 molec.−1 s−1. The relatively low rate coefficient is in good agreement with the theoretical result of 3×10-14 cm3 molec.−1 s−1 at 298 K, increasing to ∼6×10-14 cm3 molec.−1 s−1 in the cold upper troposphere but with associated uncertainty of a factor of 2. The reaction proceeds mainly via abstraction of the peroxidic hydrogen via a relatively weakly bonded and short-lived prereaction complex, in which H abstraction occurs only slowly due to a high barrier and low tunnelling probabilities. Our results imply that the lifetime of CH3C(O)OOH with respect to OH-initiated degradation in the atmosphere is of the order of 1 year (not days as previously believed) and that its major sink in the free and upper troposphere is likely to be photolysis, with deposition important in the boundary layer.

scholarly journals The atmospheric chemistry of sulphuryl fluoride, SO<sub>2</sub>F<sub>2</sub>

2007 ◽  
Vol 7 (5) ◽  
pp. 15213-15249
Author(s):  
T. J. Dillon ◽  
A. Horowitz ◽  
J. N. Crowley
Keyword(s):  
Atmospheric Chemistry ◽  
Rate Coefficient ◽  
Relative Rate ◽  
Significant Loss ◽  
Rate Coefficients ◽  
Atmospheric Species ◽  
Upper Limits ◽  
Wall Flow ◽  
Temperature Rate ◽  
Good Agreement

Abstract. The atmospheric chemistry of sulphuryl fluoride, SO2F2, was investigated in a series of laboratory studies. A competitive rate method, using pulsed laser photolysis (PLP) to generate O(1D) coupled to detection of OH by laser induced fluorescence (LIF), was used to determine the overall rate coefficient for the reaction O(1D)+SO2F2 → products (R1) of k1 (220–300 K)=(1.3±0.2)×10−10 cm³ molecule−1 s−1. Monitoring the O(³P) product (R1a) enabled the contribution (α) of the physical quenching process (in which SO2F2 is not consumed) to be determined as α1 (225–296 K)=(0.55±0.04). Separate, relative rate measurements at 298 K provided a rate coefficient for reactive loss of O(1D), k1b, of (5.8±0.8)×10−11 cm³ molecule−1 s−1 in good agreement with the value calculated from (1−α)×k1=(5.9±1.0)×10−11 cm³ molecule−1 s−1. Upper limits for the rate coefficients for reaction of SO2F2 with OH (R2, using PLP-LIF), and with O3 (R3, static reactor) were determined as k2 (294 K)<1×10−15 cm³ molecule−1 s−1 and k3 (294 K)<1×10−23 cm³ molecule−1 s−1. In experiments using the wetted-wall flow tube technique, no loss of SO2F2 onto aqueous surfaces was observed, allowing an upper limit for the uptake coefficient of γ(pH 2–12)<1×10−7 to be determined. These results indicate that SO2F2 has no significant loss processes in the troposphere, and a very long stratospheric lifetime. Integrated band intensities for SO2F2 infrared absorption features between 6 and 19 μm were obtained, and indicate a significant global warming potential for this molecule. In the course of this work, ambient temperature rate coefficients for the reactions O(1D) with several important atmospheric species were determined. The results (in units of 10−10 cm³ molecule−1 s−1), k(O1D+N2)=(0.33±0.06); k(O1D+N2O)=(1.47±0.2) and k(O1D+H2O)=(1.94±0.5) were in good agreement with other recent determinations.

scholarly journals The study of intermolecular energy transfers in electronic energy quenching for molecular collisions N<sub>2</sub>-N<sub>2</sub>, N<sub>2</sub>-O<sub>2</sub>, O<sub>2</sub>-O<sub>2</sub>

2008 ◽  
Vol 26 (5) ◽  
pp. 1149-1157 ◽  
Author(s):  
A. S. Kirillov
Keyword(s):  
Vibrational Excitation ◽  
Branching Ratios ◽  
Electronic Energy ◽  
Rate Coefficients ◽  
Molecular Collisions ◽  
Calculated Rate ◽  
Energy Transfers ◽  
Intermolecular Energy ◽  
Product Branching ◽  
Good Agreement

Abstract. Contributions of intermolecular electron energy transfers in the electronic quenching are calculated for molecular collisions N2(A3Σu+, W3Δu)+N2(X1Σg+, v=0), N2(A3Σu+)+N2(X1Σg+, v≥0), N2(A3Σu+)+O2(X3Σg−, v=0–2), O2(a1Δg, b1Σg+)+O2(X3Σg−, v=0–2). The calculation has allowed one to estimate the product branching ratios. It is shown that there is a dependence of the calculated rate coefficients on the vibrational excitation of N2(X1Σg+) and O2(X3Σg−) molecules. In many cases, the calculated rate coefficients have a good agreement with available experimental data.

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