1
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Zhang S, Chen Q, Zhang L, Li J, Hu X, Xie D. Dynamics studies for the multi-well and multi-channel reaction of OH with C 2H 2 on a full-dimensional global potential energy surface. Phys Chem Chem Phys 2024; 26:7351-7362. [PMID: 38375620 DOI: 10.1039/d3cp05811e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/21/2024]
Abstract
The C2H2 + OH reaction is an important acetylene oxidation pathway in the combustion process, as well as a typical multi-well and multi-channel reaction. Here, we report an accurate full-dimensional machine learning-based potential energy surface (PES) for the C2H2 + OH reaction at the UCCSD(T)-F12b/cc-pVTZ-F12 level, based on about 475 000 ab initio points. Extensive quasi-classical trajectory (QCT) calculations were performed on the newly developed PES to obtain detailed dynamic data and analyze reaction mechanisms. Below 1000 K, the C2H2 + OH reaction produces H + OCCH2 and CO + CH3. With increasing temperature, the product channels H2O + C2H and H + HCCOH are accessible and the former dominates above 1900 K. It is found that the formation of H2O + C2H is dominated by a direct reaction process, while other channels belong to the indirect mechanism involving long-lived intermediates along the reaction pathways. At low temperatures, the C2H2 + OH reaction behaves like an unimolecular reaction due to the unique PES topographic features, of which the dynamic features are similar to the decomposition of energy-rich complexes formed by C2H2 + OH collision. The classification of trajectories that undergo different reaction pathways to generate each product and their product energy distributions were also reported in this work. This dynamic information may provide a deep understanding of the C2H2 + OH reaction.
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Affiliation(s)
- Shuwen Zhang
- Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Qixin Chen
- Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
| | - Lidong Zhang
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, China; State Key Laboratory of Fire Science, University of Science and Technology of China, Hefei 230026, China.
| | - Jun Li
- School of Chemistry and Chemical Engineering & Chongqing Key Laboratory of Theoretical and Computational Chemistry, Chongqing University, Chongqing 401331, China.
| | - Xixi Hu
- Kuang Yaming Honors School, Nanjing University, Nanjing 210023, China.
- Hefei National Laboratory, Hefei 230088, China
| | - Daiqian Xie
- Institute of Theoretical and Computational Chemistry, Key Laboratory of Mesoscopic Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China
- Hefei National Laboratory, Hefei 230088, China
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2
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Upadhyaya HP. Theoretical study on the gas phase hydroxyl radical reaction with tetrahydrothiophene, tetrahydrofuran, thiophene and furan. Chem Phys Lett 2023. [DOI: 10.1016/j.cplett.2023.140385] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/25/2023]
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3
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Hu X, Yu X, Hou H, Wang B. Theoretical Investigations on the Hydroxyl-Initialized Oxidation of Hexafluoro-2-butyne in the Presence of Oxygen. J Phys Chem A 2022; 126:1994-2006. [PMID: 35298178 DOI: 10.1021/acs.jpca.2c00613] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Hexafluoro-2-butyne (C4F6) is a potential eco-friendly alternative gas in plasma, refrigerants, and electrical insulation applications. Mechanisms for the reactions of C4F6 with OH/O2 have been revealed in detail using various theoretical methods including ROCBS-Q, RCCSD(T), multireference RS2C, and extrapolations to the complete basis-set limit with Aug-cc-pVnZ (n = T, Q, 5) basis sets. Rate coefficients and product branching ratios were predicted for a wide range of temperatures and pressures using the solution of master equations. The vibrationally adiabatic ground-state barrier for the initial C4F6 + OH association was best estimated to be 1.53-2.26 kcal/mol. Energetically preferable decomposition paths for the conformation-dependent C4F6OH adducts include six-center HF elimination, four-center proton migration, and C-C bond cleavage, but the collisional deactivation is dominant under ambient conditions. The subsequent oxidation of C4F6OH by O2 bifurcates in two orientations and proceeds without any well-defined barrier followed by the successive isomerization/elimination steps, forming perfluorobiacetyl to regenerate OH radicals or trifluoroacetic acid with trifluoroacetyl radicals. The OH-recycling path accounts for a branching ratio of 70% under ambient conditions. Theoretical rate coefficients are in good agreement with the available experimental results. The effect of fluorination on the reactivity of alkynes toward OH/O2 is discussed.
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Affiliation(s)
- Xiaoyi Hu
- College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, People's Republic of China
| | - Xiaojuan Yu
- College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, People's Republic of China
| | - Hua Hou
- College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, People's Republic of China
| | - Baoshan Wang
- College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, People's Republic of China
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4
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Upadhyaya HP. Gas phase hydroxyl radical reaction with 3,4-Dichloro-1,2,5-thiadiazole in the temperature range of 265–353 K: A kinetic and theoretical study. Chem Phys Lett 2021. [DOI: 10.1016/j.cplett.2021.138828] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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5
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Arathala P, Tangtartharakul CB, Sinha A. Atmospheric Ring-Closure and Dehydration Reactions of 1,4-Hydroxycarbonyls in the Gas Phase: The Impact of Catalysts. J Phys Chem A 2021; 125:5963-5975. [PMID: 34191509 DOI: 10.1021/acs.jpca.1c02331] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
1,4-Hydroxycarbonyls can potentially undergo sequential reactions involving cyclization followed by dehydration to form dihydrofurans. As dihydrofurans contain a double bond, they are highly reactive toward atmospheric oxidants such as OH, O3, and NO3. In the present study, we use ab initio calculations to examine the impact of various atmospheric catalysts on the energetics and kinetics of the gas-phase cyclization and dehydration reaction steps associated with 4-hydroxybutanal, a prototypical 1,4-hydroxycarbonyl molecule. The cyclization step transforms 4-hydroxybutanal into 2-hydroxytetrahydrofuran, which can subsequently undergo dehydration to form 2,3-dihydrofuran. As the barriers associated with the cyclization and dehydration steps for 4-hydroxybutanal are, respectively, 34.8 and 63.0 kcal/mol in the absence of a catalyst, both reaction steps are inaccessible under atmospheric conditions in the gas phase. However, the presence of a suitable catalyst can significantly reduce the reaction barriers, and we have examined the impact of a single molecule of H2O, HO2 radical, HC(O)OH, HNO3, and H2SO4 on these reactions. We find that H2SO4 reduces the reaction barriers the greatest, with the barrier for the cyclization step being reduced to -13.1 kcal/mol and that for the dehydration step going down to 9.2 kcal/mol, measured relative to their respective separated starting reactants. Interestingly, our kinetic study shows that HNO3 gives the fastest rate due to the combined effects of a larger atmospheric concentration and a reduced barrier. Thus, our study suggests that, with acid catalysis, the cyclization reaction step can readily occur for 1,4-hydroxycarbonyls in the gas phase. Because the dehydration step exhibits a significant barrier even with acid catalysis, the 2-hydroxytetrahydrofuran products, once formed, are likely lost through their reaction with OH radicals in the atmosphere. We have investigated the reaction pathways and the rate constant for this bimolecular reaction in the presence of excess molecular oxygen (3O2), as it would occur under tropospheric conditions, using computational chemistry over the 200-300 K temperature range. We find that the main products from these OH-initiated oxidation reactions are succinaldehyde + HO2 and 2,3-dihydro-2-furanol + HO2.
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Affiliation(s)
- Parandaman Arathala
- Department of Chemistry and Biochemistry, University of California-San Diego, La Jolla, California 92093, United States
| | - Chanin B Tangtartharakul
- Department of Chemistry and Biochemistry, University of California-San Diego, La Jolla, California 92093, United States
| | - Amitabha Sinha
- Department of Chemistry and Biochemistry, University of California-San Diego, La Jolla, California 92093, United States
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6
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Medeiros DJ, Robertson SH, Blitz MA, Seakins PW. Direct Trace Fitting of Experimental Data Using the Master Equation: Testing Theory and Experiments on the OH + C 2H 4 Reaction. J Phys Chem A 2020; 124:4015-4024. [PMID: 32353235 DOI: 10.1021/acs.jpca.0c02132] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Laser flash photolysis coupled with laser-induced fluorescence observation of OH has been used to observe the equilibration of OH + C2H4 ↔ HOC2H4 over the temperature range 563-723 K and pressures of bath gas (N2) from 58 to 250 Torr. The time-resolved OH traces have been directly and globally fitted with a master equation in order to extract ΔRH00, the binding energy of the HOC2H4 adduct, with respect to reagents. The global approach allows the role that OH abstraction plays at higher temperatures to be identified. The resultant value ofΔRH00, 111.8 kJ mol-1, is determined to be better than 2 kJ mol-1 and is in agreement with our ab initio calculations (carried out at the CCSD(T)/CBS//M06-2X/aug-cc-pVTZ level), 111.4 kJ mol-1, and other state of the art calculations. Parameters for the abstraction channel are also in good agreement with previous experimental studies. To effect this analysis, the MESMER master equation code was extended to directly incorporate secondary chemistry: diffusional loss from the observation region and reaction with the photolytic precursor. These extensions, which, among other things, resolve issues related to the merging of chemically significant and internal energy relaxation eigenvalues, are presented.
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Affiliation(s)
| | - S H Robertson
- Dassault Systèmes, 334 Science Park, Milton Road, Cambridge CB4 0WN, United Kingdom
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7
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Cavallotti C, Pelucchi M, Georgievskii Y, Klippenstein SJ. EStokTP: Electronic Structure to Temperature- and Pressure-Dependent Rate Constants—A Code for Automatically Predicting the Thermal Kinetics of Reactions. J Chem Theory Comput 2018; 15:1122-1145. [DOI: 10.1021/acs.jctc.8b00701] [Citation(s) in RCA: 57] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- C. Cavallotti
- Department of Chemistry, Materials and Chemical Engineering “G. Natta”, Politecnico di Milano, Milan, Italy
| | - M. Pelucchi
- Department of Chemistry, Materials and Chemical Engineering “G. Natta”, Politecnico di Milano, Milan, Italy
| | - Y. Georgievskii
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
| | - S. J. Klippenstein
- Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
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8
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Stone D, Au K, Sime S, Medeiros DJ, Blitz M, Seakins PW, Decker Z, Sheps L. Unimolecular decomposition kinetics of the stabilised Criegee intermediates CH 2OO and CD 2OO. Phys Chem Chem Phys 2018; 20:24940-24954. [PMID: 30238099 DOI: 10.1039/c8cp05332d] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Decomposition kinetics of stabilised CH2OO and CD2OO Criegee intermediates have been investigated as a function of temperature (450-650 K) and pressure (2-350 Torr) using flash photolysis coupled with time-resolved cavity-enhanced broadband UV absorption spectroscopy. Decomposition of CD2OO was observed to be faster than CH2OO under equivalent conditions. Production of OH radicals following CH2OO decomposition was also monitored using flash photolysis with laser-induced fluorescence (LIF), with results indicating direct production of OH in the v = 0 and v = 1 states in low yields. Master equation calculations performed using the Master Equation Solver for Multi-Energy well Reactions (MESMER) enabled fitting of the barriers for the decomposition of CH2OO and CD2OO to the experimental data. Parameterisations of the decomposition rate coefficients, calculated by MESMER, are provided for use in atmospheric models and implications of the results are discussed. For CH2OO, the MESMER fits require an increase in the calculated barrier height from 78.2 kJ mol-1 to 81.8 kJ mol-1 using a temperature-dependent exponential down model for collisional energy transfer with ΔEdown = 32.6(T/298 K)1.7 cm-1 in He. The low- and high-pressure limit rate coefficients are k1,0 = 3.2 × 10-4(T/298)-5.81exp(-12 770/T) cm3 s-1 and k1,∞ = 1.4 × 1013(T/298)0.06exp(-10 010/T) s-1, with median uncertainty of ∼12% over the range of experimental conditions used here. Extrapolation to atmospheric conditions yields k1(298 K, 760 Torr) = 1.1+1.5-1.1 × 10-3 s-1. For CD2OO, MESMER calculations result in ΔEdown = 39.6(T/298 K)1.3 cm-1 in He and a small decrease in the calculated barrier to decomposition from 81.0 kJ mol-1 to 80.1 kJ mol-1. The fitted rate coefficients for CD2OO are k2,0 = 5.2 × 10-5(T/298)-5.28exp(-11 610/T) cm3 s-1 and k2,∞ = 1.2 × 1013(T/298)0.06exp(-9800/T) s-1, with overall error of ∼6% over the present range of temperature and pressure. The extrapolated k2(298 K, 760 Torr) = 5.5+9.2-5.5 × 10-3 s-1. The master equation calculations for CH2OO indicate decomposition yields of 63.7% for H2 + CO2, 36.0% for H2O + CO and 0.3% for OH + HCO with no significant dependence on temperature between 400 and 1200 K or pressure between 1 and 3000 Torr.
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Affiliation(s)
- Daniel Stone
- School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK.
| | - Kendrew Au
- Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94551, USA.
| | - Samantha Sime
- School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK.
| | | | - Mark Blitz
- School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK.
| | - Paul W Seakins
- School of Chemistry, University of Leeds, Leeds, LS2 9JT, UK.
| | - Zachary Decker
- Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94551, USA.
| | - Leonid Sheps
- Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94551, USA.
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9
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Bejan IG, Winiberg FAF, Mortimer N, Medeiros DJ, Brumby CA, Orr SC, Kelly J, Seakins PW. Gas-phase rate coefficients for a series of alkyl cyclohexanes with OH radicals and Cl atoms. INT J CHEM KINET 2018. [DOI: 10.1002/kin.21179] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Iustinian G. Bejan
- School of Chemistry; University of Leeds; Leeds; United Kingdom
- Faculty of Chemistry and “Integrated Centre for Environmental Science Studies in the North-East Development Region - CERNESIM”; “Al. I. Cuza” University of Iasi; Iasi; Romania
| | | | | | | | | | | | - Jamie Kelly
- School of Chemistry; University of Leeds; Leeds; United Kingdom
| | - Paul W. Seakins
- School of Chemistry; University of Leeds; Leeds; United Kingdom
- National Centre for Atmospheric Science; University of Leeds; Leeds; United Kingdom
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10
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Adams JD, Scrape PG, Lee SH, Butler LJ. Dissociative Photoionization of the Elusive Vinoxy Radical. J Phys Chem A 2017; 121:6262-6268. [PMID: 28806080 DOI: 10.1021/acs.jpca.7b04730] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
These experiments report the dissociative photoionization of vinoxy radicals to m/z = 15 and 29. In a crossed laser-molecular beam scattering apparatus, we induce C-Cl bond fission in 2-chloroacetaldehyde by photoexcitation at 157 nm. Our velocity measurements, combined with conservation of angular momentum, show that 21% of the C-Cl photofission events form vinoxy radicals that are stable to subsequent dissociation to CH3 + CO or H + ketene. Photoionization of these stable vinoxy radicals, identified by their velocities, which are momentum-matched with the higher-kinetic-energy Cl atom photofragments, shows that the vinoxy radicals dissociatively photoionize to give signal at m/z = 15 and 29. We calibrated the partial photoionization cross section of vinoxy to CH3+ relative to the bandwidth-averaged photoionization cross section of the Cl atom at 13.68 eV to put the partial photoionization cross sections on an absolute scale. The resulting bandwidth-averaged partial cross sections are 0.63 and 1.3 Mb at 10.5 and 11.44 eV, respectively. These values are consistent with the upper limit to the cross section estimated from a study by Savee et al. on the O(3P) + propene bimolecular reaction. We note that the uncertainty in these values is primarily dependent on the signal attributed to C-Cl primary photofission in the m/z = 35 (Cl+) time-of-flight data. While the value is a rough estimate, the bandwidth-averaged partial photoionization cross section of vinoxy to HCO+ calculated from the signal at m/z = 29 at 11.53 eV is approximately half that of vinoxy to CH3+. We also present critical points on the potential energy surface of the vinoxy cation calculated at the G4//B3LYP/6-311++G(3df,2p) level of theory to support the observation of dissociative ionization of vinoxy to both CH3+ and HCO+.
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Affiliation(s)
- Jonathan D Adams
- The James Franck Institute and Department of Chemistry, The University of Chicago , Chicago, Illinois 60637, United States
| | - Preston G Scrape
- The James Franck Institute and Department of Chemistry, The University of Chicago , Chicago, Illinois 60637, United States
| | - Shih-Huang Lee
- National Synchrotron Radiation Research Center , Hsinchu 30076, Taiwan, Republic of China
| | - Laurie J Butler
- The James Franck Institute and Department of Chemistry, The University of Chicago , Chicago, Illinois 60637, United States
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11
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Blitz MA, Salter RJ, Heard DE, Seakins PW. An Experimental and Master Equation Study of the Kinetics of OH/OD + SO 2: The Limiting High-Pressure Rate Coefficients. J Phys Chem A 2017; 121:3184-3191. [PMID: 28365987 DOI: 10.1021/acs.jpca.7b01295] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The kinetics of the reaction OH/OD + SO2 were studied using a laser flash photolysis/laser-induced fluorescence technique. Evidence for two-photon photolysis of SO2 at 248 nm is presented and quantified, and which appears to have been evident to some extent in most previous photolysis studies, potentially leading to values for the rate coefficient k1 that are too large. The kinetics of the reaction OH(v = 0) + SO2 (T = 295 K, p = 25-300 torr) were measured under conditions where SO2 photolysis was taken into account. These results, together with literature data, were modeled using a master equation analysis. This analysis highlighted problems with the literature data: the rate coefficients derived from flash photolysis data were generally too high and from the flow tube data too low. Our best estimate of the high-pressure limiting rate coefficient k1∞ was obtained from selected data and gives a value of (7.8 ± 2.2) × 10-13 cm3 molecule-1 s-1, which is lower than that recommended in the literature. A parametrized form of k1([N2],T) is provided. The OD(v = 0) + SO2 (T = 295 K, p = 25-300 torr) data are reported for the first time, and master equation analysis reinforces our assignment of k1∞.
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Affiliation(s)
| | - Robert J Salter
- Deloitte MCS , 3 Rivergate, Temple Quay, Bristol BR1 6GD, U.K
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12
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Blitz MA, Salter RJ, Heard DE, Seakins PW. An Experimental Study of the Kinetics of OH/OD(v = 1,2,3) + SO 2: The Limiting High-Pressure Rate Coefficients as a Function of Temperature. J Phys Chem A 2017; 121:3175-3183. [PMID: 28363245 DOI: 10.1021/acs.jpca.7b01294] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The kinetics of the reaction OH/OD(v = 1,2,3) + SO2 were studied using a photolysis/laser-induced fluorescence technique. The rate coefficients OH/OD(v = 1,2,3) + SO2, k1, over the temperature range of 295-810 K were used to determine the limiting high-pressure limit k1∞. This method is usually applicable if the reaction samples the potential well of the adduct HOSO2 and if intramolecular vibrational relaxation is fast. In the present case, however, the rate coefficients showed an additional fast removal contribution as evidenced by the increase in k1 with vibrational level; this behavior together with its temperature dependence is consistent with the existence of a weakly bound complex on the potential energy surface prior to adduct formation. The data were analyzed using a composite mechanism that incoporates energy-transfer mechanisms via both the adduct and the complex, and yielded a value of k1∞(295 K) equal to (7.2 ± 3.3) × 10-13 cm3 molecule-1 s-1 (errors at 1σ), a factor of between 2 and 3 smaller than the current recommended IUPAC and JPL values of (2.0-1.0+2.0) and (1.6 ± 0.4) × 10-12 cm3 molecule-1 s-1 at 298 K, respectively, although the error bars do overlap. k1∞ was observed to only depend weakly on temperature. Further evidence for a smaller k1∞ is presented in the companion paper.
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Affiliation(s)
| | - Robert J Salter
- Deloitee MCS , 3 Rivergate, Temple Quay, Bristol BR1 6GD, U.K
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13
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Wang H, You X, Blitz MA, Pilling MJ, Robertson SH. Obtaining effective rate coefficients to describe the decomposition kinetics of the corannulene oxyradical at high temperatures. Phys Chem Chem Phys 2017; 19:11064-11074. [DOI: 10.1039/c7cp00639j] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This work analyzes the effect of overlapping eigenvalues on the high-temperature kinetics of a large oxyradical based on master equation solutions.
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Affiliation(s)
- Hongmiao Wang
- Center for Combustion Energy
- Tsinghua University
- Beijing
- China
- Key Laboratory for Thermal Science and Power Engineering of Ministry of Education
| | - Xiaoqing You
- Center for Combustion Energy
- Tsinghua University
- Beijing
- China
- Key Laboratory for Thermal Science and Power Engineering of Ministry of Education
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14
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Gimenez-Lopez J, Rasmussen CT, Hashemi H, Alzueta MU, Gao Y, Marshall P, Goldsmith CF, Glarborg P. Experimental and Kinetic Modeling Study of C2H2Oxidation at High Pressure. INT J CHEM KINET 2016. [DOI: 10.1002/kin.21028] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Jorge Gimenez-Lopez
- Department of Chemical and Biochemical Engineering; Technical University of Denmark; DK-2800 Kgs. Lyngby Denmark
- Department of Chemical and Environmental Engineering; University of Zaragoza; 50018 Zaragoza Spain
| | - Christian Tihic Rasmussen
- Department of Chemical and Biochemical Engineering; Technical University of Denmark; DK-2800 Kgs. Lyngby Denmark
| | - Hamid Hashemi
- Department of Chemical and Biochemical Engineering; Technical University of Denmark; DK-2800 Kgs. Lyngby Denmark
| | - Maria U. Alzueta
- Department of Chemical and Environmental Engineering; University of Zaragoza; 50018 Zaragoza Spain
| | - Yide Gao
- Department of Chemistry and Center for Advanced Scientific Computing and Modeling; University of North Texas; 1155 Union Circle #305070 Denton Texas 76203-5017
| | - Paul Marshall
- Department of Chemistry and Center for Advanced Scientific Computing and Modeling; University of North Texas; 1155 Union Circle #305070 Denton Texas 76203-5017
| | | | - Peter Glarborg
- Department of Chemical and Biochemical Engineering; Technical University of Denmark; DK-2800 Kgs. Lyngby Denmark
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15
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Sato S. Empirical rate equation for association reactions and ion–molecule reactions. Chem Phys 2016. [DOI: 10.1016/j.chemphys.2016.02.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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16
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Lam CS, Adams JD, Butler LJ. The Onset of H + Ketene Products from Vinoxy Radicals Prepared by Photodissociation of Chloroacetaldehyde at 157 nm. J Phys Chem A 2016; 120:2521-36. [PMID: 27091706 DOI: 10.1021/acs.jpca.6b01256] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We investigate the unimolecular dissociation of the vinoxy radical (CH2CHO) prepared with high internal energy imparted from the photodissociation of chloroacetaldehyde (CH2ClCHO) at 157 nm. Using a velocity map imaging apparatus, we measured the speed distribution of the recoiling chlorine atoms, Cl((2)P3/2) and Cl((2)P1/2), and derived from this the resulting distribution of kinetic energy, P(ET), imparted to the Cl + vinoxy fragments upon dissociation. Using conservation of energy, the distribution of kinetic energy was used to determine the total internal energy distribution in the radical. The P(ET) derived for the C-Cl bond fission presented in this work suggests the vinoxy radicals are mostly formed in the à state. We also took ion images at m/z = 42 and m/z = 15 to characterize the branching between the unimolecular dissociation channels of the vinoxy radical to H + ketene and methyl + CO products. Our results show a marked change in the branching ratio between the two channels from the previous study on the photodissociation of chloroacetaldehyde at 193 nm by Miller et al. (J. Chem. Phys., 2004, 121, 1830) in that the production of ketene is now favored over the production of methyl. To help analyze the data, we developed a model for the branching between the two channels that takes into account how the change in rotational energy en route to the products affects the vibrational energy available to surmount the barriers to the channels. The model predicts the portion of the C-Cl bond fission P(ET) that produces dissociative vinoxy radicals, then predicts the branching ratio between the H + ketene and CH3 + CO product channels at each ET. The model uses Rice-Ramsperger-Kassel-Marcus rate constants at the correct sums and densities of vibrational states while accounting for angular momentum conservation. We find that the predicted portion of the P(ET) that produces H + ketene products best fits the experimental portion (that we derive by taking advantage of conservation of momentum) if we use a barrier height for the H + ketene channel that is 4.0 ± 0.5 kcal/mol higher than the isomerization barrier en route to CH3 + CO products. Using the G4 computed isomerization barrier of 40.6 kcal/mol, this gives an experimentally determined barrier to the H + ketene channel of 44.6 kcal/mol. From these calculations, we also predict the branching ratio between the H + ketene and methyl + CO channels to be ∼2.1:1.
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Affiliation(s)
- Chow-Shing Lam
- The James Franck Institute and Department of Chemistry, The University of Chicago , Chicago, Illinois 60637 United States
| | - Jonathan D Adams
- The James Franck Institute and Department of Chemistry, The University of Chicago , Chicago, Illinois 60637 United States
| | - Laurie J Butler
- The James Franck Institute and Department of Chemistry, The University of Chicago , Chicago, Illinois 60637 United States
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McKee K, Blitz MA, Pilling MJ. Temperature and Pressure Studies of the Reactions of CH3O2, HO2, and 1,2-C4H9O2 with NO2. J Phys Chem A 2015; 120:1408-20. [DOI: 10.1021/acs.jpca.5b06306] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Kenneth McKee
- School of Chemistry and ‡National Centre
for Atmospheric Science, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Mark A. Blitz
- School of Chemistry and ‡National Centre
for Atmospheric Science, University of Leeds, Leeds, LS2 9JT, United Kingdom
| | - Michael J. Pilling
- School of Chemistry and ‡National Centre
for Atmospheric Science, University of Leeds, Leeds, LS2 9JT, United Kingdom
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18
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Vereecken L, Glowacki DR, Pilling MJ. Theoretical Chemical Kinetics in Tropospheric Chemistry: Methodologies and Applications. Chem Rev 2015; 115:4063-114. [DOI: 10.1021/cr500488p] [Citation(s) in RCA: 146] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Luc Vereecken
- Max Planck Institute for Chemistry, 55128 Mainz, Germany
| | - David R. Glowacki
- PULSE
Institute and Department of Chemistry, Stanford University, Stanford, California 94305, United States
- SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
- School
of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom
- Department
of Computer Science, University of Bristol, Bristol BS8 1UB, United Kingdom
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19
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Onel L, Blitz M, Dryden M, Thonger L, Seakins P. Branching ratios in reactions of OH radicals with methylamine, dimethylamine, and ethylamine. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2014; 48:9935-9942. [PMID: 25072999 DOI: 10.1021/es502398r] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The branching ratios for the reaction of the OH radical with the primary and secondary alkylamines: methylamine (MA), dimethylamine (DMA), and ethylamine (EA), have been determined using the technique of pulsed laser photolysis-laser-induced fluorescence. Titration of the carbon-centered radical, formed following the initial OH abstraction, with oxygen to give HO2 and an imine, followed by conversion of HO2 to OH by reaction with NO, resulted in biexponential OH decay traces on a millisecond time scale. Analysis of the biexponential curves gave the HO2 yield, which equaled the branching ratio for abstraction at αC-H position, r(αC-H). The technique was validated by reproducing known branching ratios for OH abstraction for methanol and ethanol. For the amines studied in this work (all at 298 K): r(αC-H,MA) = 0.76 ± 0.08, r(αC-H,DMA) = 0.59 ± 0.07, and r(αC-H,EA) = 0.49 ± 0.06 where the errors are a combination in quadrature of statistical errors at the 2σ level and an estimated 10% systematic error. The branching ratios r(αC-H) for OH reacting with (CH3)2NH and CH3CH2NH2 are in agreement with those obtained for the OD reaction with (CH3)2ND (d-DMA) and CH3CH2ND2 (d-EA): r(αC-H,d-DMA) = 0.71 ± 0.12 and r(αC-H,d-EA) = 0.54 ± 0.07. A master equation analysis (using the MESMER package) based on potential energy surfaces from G4 theory was used to demonstrate that the experimental determinations are unaffected by formation of stabilized peroxy radicals and to estimate atmospheric pressure yields. The branching ratio for imine formation through the reaction of O2 with α carbon-centered radicals at 1 atm of N2 are estimated as r(CH2NH2) = 0.79 ± 0.15, r(CH2NHCH3) = 0.72 ± 0.19, and r(CH3CHNH2) = 0.50 ± 0.18. The implications of this work on the potential formation of nitrosamines and nitramines are briefly discussed.
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Affiliation(s)
- Lavinia Onel
- School of Chemistry, University of Leeds , Leeds, LS2 9JT, U.K
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20
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Villano SM, Carstensen HH, Dean AM. Rate Rules, Branching Ratios, and Pressure Dependence of the HO2 + Olefin Addition Channels. J Phys Chem A 2013; 117:6458-73. [DOI: 10.1021/jp405262r] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Stephanie M. Villano
- Chemical
and Biological Engineering Department, Colorado
School of Mines, Golden Colorado 80301, United States
| | - Hans-Heinrich Carstensen
- Chemical
and Biological Engineering Department, Colorado
School of Mines, Golden Colorado 80301, United States
| | - Anthony M. Dean
- Chemical
and Biological Engineering Department, Colorado
School of Mines, Golden Colorado 80301, United States
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21
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Glowacki DR, Lockhart J, Blitz MA, Klippenstein SJ, Pilling MJ, Robertson SH, Seakins PW. Interception of excited vibrational quantum states by O2 in atmospheric association reactions. Science 2012; 337:1066-9. [PMID: 22936771 DOI: 10.1126/science.1224106] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Bimolecular reactions in Earth's atmosphere are generally assumed to proceed between reactants whose internal quantum states are fully thermally relaxed. Here, we highlight a dramatic role for vibrationally excited bimolecular reactants in the oxidation of acetylene. The reaction proceeds by preliminary adduct formation between the alkyne and OH radical, with subsequent O(2) addition. Using a detailed theoretical model, we show that the product-branching ratio is determined by the excited vibrational quantum-state distribution of the adduct at the moment it reacts with O(2). Experimentally, we found that under the simulated atmospheric conditions O(2) intercepts ~25% of the excited adducts before their vibrational quantum states have fully relaxed. Analogous interception of excited-state radicals by O(2) is likely common to a range of atmospheric reactions that proceed through peroxy complexes.
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22
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Glowacki DR, Liang CH, Morley C, Pilling MJ, Robertson SH. MESMER: An Open-Source Master Equation Solver for Multi-Energy Well Reactions. J Phys Chem A 2012; 116:9545-60. [DOI: 10.1021/jp3051033] [Citation(s) in RCA: 397] [Impact Index Per Article: 33.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | - Chi-Hsiu Liang
- School of Chemistry, University of Leeds, Leeds LS2 9JT,
U.K
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23
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Vereecken L, Francisco JS. Theoretical studies of atmospheric reaction mechanisms in the troposphere. Chem Soc Rev 2012; 41:6259-93. [DOI: 10.1039/c2cs35070j] [Citation(s) in RCA: 311] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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24
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Carr SA, Glowacki DR, Liang CH, Baeza-Romero MT, Blitz MA, Pilling MJ, Seakins PW. Experimental and Modeling Studies of the Pressure and Temperature Dependences of the Kinetics and the OH Yields in the Acetyl + O2 Reaction. J Phys Chem A 2011; 115:1069-85. [DOI: 10.1021/jp1099199] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Scott A. Carr
- School of Chemistry and ‡School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - David R. Glowacki
- School of Chemistry and ‡School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Chi-Hsiu Liang
- School of Chemistry and ‡School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - M. Teresa Baeza-Romero
- School of Chemistry and ‡School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Mark A. Blitz
- School of Chemistry and ‡School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Michael J. Pilling
- School of Chemistry and ‡School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Paul W. Seakins
- School of Chemistry and ‡School of Earth and Environment, University of Leeds, Leeds LS2 9JT, United Kingdom
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25
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Gao H, Liu JY, Sun CC. Theoretical and kinetic studies of the reactions of CF2HCFHCF2H and CF3CFHCFH2 with hydroxyl radicals. J Chem Phys 2009; 130:224301. [DOI: 10.1063/1.3147464] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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26
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Glowacki DR, Wang L, Pilling MJ. Evidence of Formation of Bicyclic Species in the Early Stages of Atmospheric Benzene Oxidation. J Phys Chem A 2009; 113:5385-96. [DOI: 10.1021/jp9001466] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- David R. Glowacki
- School of Chemistry, University of Leeds, Leeds LS2 9JT, United Kingdom, and School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou, China, 51640
| | - Liming Wang
- School of Chemistry, University of Leeds, Leeds LS2 9JT, United Kingdom, and School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou, China, 51640
| | - Michael J. Pilling
- School of Chemistry, University of Leeds, Leeds LS2 9JT, United Kingdom, and School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou, China, 51640
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27
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Maranzana A, Ghigo G, Tonachini G, Barker JR. Tropospheric Oxidation of Ethyne and But-2-yne. 1. Theoretical Mechanistic Study. J Phys Chem A 2008; 112:3656-65. [DOI: 10.1021/jp077174o] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Andrea Maranzana
- Dipartimento di Chimica Generale e Chimica Organica, Università di Torino, Corso Massimo D'Azeglio 48, I-10125 Torino, Italy, and Department of Atmospheric, Oceanic, and Space Sciences, 1520 Space Research Building, 2455 Hayward Street, University of Michigan, Ann Arbor, Michigan 48109-2143
| | - Giovanni Ghigo
- Dipartimento di Chimica Generale e Chimica Organica, Università di Torino, Corso Massimo D'Azeglio 48, I-10125 Torino, Italy, and Department of Atmospheric, Oceanic, and Space Sciences, 1520 Space Research Building, 2455 Hayward Street, University of Michigan, Ann Arbor, Michigan 48109-2143
| | - Glauco Tonachini
- Dipartimento di Chimica Generale e Chimica Organica, Università di Torino, Corso Massimo D'Azeglio 48, I-10125 Torino, Italy, and Department of Atmospheric, Oceanic, and Space Sciences, 1520 Space Research Building, 2455 Hayward Street, University of Michigan, Ann Arbor, Michigan 48109-2143
| | - John R. Barker
- Dipartimento di Chimica Generale e Chimica Organica, Università di Torino, Corso Massimo D'Azeglio 48, I-10125 Torino, Italy, and Department of Atmospheric, Oceanic, and Space Sciences, 1520 Space Research Building, 2455 Hayward Street, University of Michigan, Ann Arbor, Michigan 48109-2143
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28
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Maranzana A, Barker JR, Tonachini G. Oxidation of Ethyne and But-2-yne. 2. Master Equation Simulations. J Phys Chem A 2008; 112:3666-75. [DOI: 10.1021/jp077180k] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Andrea Maranzana
- Department of Atmospheric, Oceanic, and Space Sciences, 1520 Space Research Building, 2455 Hayward Street, University of Michigan, Ann Arbor, Michigan, 48109-2143, and Dipartimento di Chimica Generale ed Organica Applicata, Università di Torino, Corso Massimo D'Azeglio 48, I-10125 Torino, Italy
| | - John R. Barker
- Department of Atmospheric, Oceanic, and Space Sciences, 1520 Space Research Building, 2455 Hayward Street, University of Michigan, Ann Arbor, Michigan, 48109-2143, and Dipartimento di Chimica Generale ed Organica Applicata, Università di Torino, Corso Massimo D'Azeglio 48, I-10125 Torino, Italy
| | - Glauco Tonachini
- Department of Atmospheric, Oceanic, and Space Sciences, 1520 Space Research Building, 2455 Hayward Street, University of Michigan, Ann Arbor, Michigan, 48109-2143, and Dipartimento di Chimica Generale ed Organica Applicata, Università di Torino, Corso Massimo D'Azeglio 48, I-10125 Torino, Italy
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29
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Pilling MJ. Interactions between theory and experiment in the investigation of elementary reactions of importance in combustion. Chem Soc Rev 2008; 37:676-85. [PMID: 18362976 DOI: 10.1039/b715767c] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Elementary reactions are a central component of models of combustion processes. Rate constants and channel yields are needed for those models. Both experimental and theoretical methods used to determine such rate data are discussed in this tutorial review, which is of interest to reaction kinetics and combustion engineering communities. Applications to combustion present particular problems because the conditions required can be well outside the ranges of temperature and pressure accessible to experiment, and the rate data can show a complex dependence on conditions. Under these conditions, the interplay between theory and experiment becomes important.
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30
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Taylor SE, Goddard A, Blitz MA, Cleary PA, Heard DE. Pulsed Laval nozzle study of the kinetics of OH with unsaturated hydrocarbons at very low temperatures. Phys Chem Chem Phys 2008; 10:422-37. [DOI: 10.1039/b711411g] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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31
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Gannon KL, Glowacki DR, Blitz MA, Hughes KJ, Pilling MJ, Seakins PW. H Atom Yields from the Reactions of CN Radicals with C2H2, C2H4, C3H6, trans-2-C4H8, and iso-C4H8. J Phys Chem A 2007; 111:6679-92. [PMID: 17536788 DOI: 10.1021/jp0689520] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The kinetics and H atom channel yield at both 298 and 195 K have been determined for reactions of CN radicals with C2H2 (1.00+/-0.21, 0.97+/-0.20), C2H4 (0.96+/-0.032, 1.04+/-0.042), C3H6 (pressure dependent), iso-C4H8 (pressure dependent), and trans-2-C4H8 (0.039+/-0.019, 0.029+/-0.047) where the first figure in each bracket is the H atom yield at 298 K and the second is that at 195 K. The kinetics of all reactions were studied by monitoring both CN decay and H atom growth by laser-induced fluorescence at 357.7 and 121.6 nm, respectively. The results are in good agreement with previous studies where available. The rate coefficients for the reaction of CN with trans-2-butene and iso-butene have been measured at 298 and 195 K for the first time, and the rate coefficients are as follows: k298K=(2.93+/-0.23)x10(-10) cm3 molecule(-1) s(-1), k195K=(3.58+/-0.43)x10(-10) cm3 molecule(-1) s(-1) and k298K=(3.17+/-0.10)x10(-10) cm3 molecule(-1) s(-1), k195K=(4.32+/-0.35)x10(-10) cm3 molecule(-1) s(-1), respectively, where the errors represent a combination of statistical uncertainty (2sigma) and an estimate of possible systematic errors. A potential energy surface for the CN+C3H6 reaction has been constructed using G3X//UB3LYP electronic structure calculations identifying a number of reaction channels leading to either H, CH3, or HCN elimination following the formation of initial addition complexes. Results from the potential energy surface calculations have been used to run master equation calculations with the ratio of primary:secondary addition, the average amount of downward energy transferred in a collision DeltaEd, and the difference in barrier heights between H atom elimination and an H atom 1, 2 migration as variable parameters. Excellent agreement is obtained with the experimental 298 K H atom yields with the following parameter values: secondary addition complex formation equal to 80%, DeltaEd=145 cm(-1), and the barrier height for H atom elimination set 5 kJ mol(-1) lower than the barrier for migration. Finally, very low temperature master equation simulations using the best fit parameters have been carried out in an increased precision environment utilizing quad-double and double-double arithmetic to predict H and CH3 yields for the CN+C3H6 reaction at temperatures and pressures relevant to Titan. The H and CH3 yields predicted by the master equation have been parametrized in a simple equation for use in modeling.
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Affiliation(s)
- Kelly L Gannon
- School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom
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32
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Baeza-Romero MT, Glowacki DR, Blitz MA, Heard DE, Pilling MJ, Rickard AR, Seakins PW. A combined experimental and theoretical study of the reaction between methylglyoxal and OH/OD radical: OH regeneration. Phys Chem Chem Phys 2007; 9:4114-28. [PMID: 17687462 DOI: 10.1039/b702916k] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Experimental studies have been conducted to determine the rate coefficient and mechanism of the reaction between methylglyoxal (CH(3)COCHO, MGLY) and the OH radical over a wide range of temperatures (233-500 K) and pressures (5-300 Torr). The rate coefficient is pressure independent with the following temperature dependence: k(3)(T) = (1.83 +/- 0.48) x 10(-12) exp((560 +/- 70)/T) cm(3) molecule(-1) s(-1) (95% uncertainties). Addition of O(2) to the system leads to recycling of OH. The mechanism was investigated by varying the experimental conditions ([O(2)], [MGLY], temperature and pressure), and by modelling based on a G3X potential energy surface, rovibrational prior distribution calculations and master equation RRKM calculations. The mechanism can be described as follows: Addition of oxygen to the system shows that process (4) is fast and that CH(3)COCO completely dissociates. The acetyl radical formed from reaction (4) reacts with oxygen to regenerate OH radicals (5a). However, a significant fraction of acetyl radical formed by reaction (R4) is sufficiently energised to dissociate further to CH(3) + CO (R4b). Little or no pressure quenching of reaction (R4b) was observed. The rate coefficient for OD + MGLY was measured as k(9)(T) = (9.4 +/- 2.4) x 10(-13) exp((780 +/- 70)/T) cm(3) molecule(-1) s(-1) over the temperature range 233-500 K. The reaction shows a noticeable inverse (k(H)/k(D) < 1) kinetic isotope effect below room temperature and a slight normal kinetic isotope effect (k(H)/k(D) > 1) at high temperature. The potential atmospheric implications of this work are discussed.
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