Shock tube study of the decomposition of cyclopentyl radicals

Awan, Iftikhar A.; Burgess, Donald R.; Tsang, Wing; Manion, Jeffrey A.

doi:10.1016/j.proci.2010.06.109

Cited by 22 publications

(61 citation statements)

References 28 publications

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“…Absolute values are derived relative to a reference reaction. In previous investigations we have determined rates corresponding to nonterminal H addition for a number of alkenes at temperatures near 1000 K. 11,17,18 While the precise degree of variation within the hydrocarbon class remains to be established, our data show that rate constants for H addition vary only slightly with the chain length of the alkene. This result is consistent with thermochemical kinetics 19 and with the studies at low temperatures.…”

Section: Introductionmentioning

confidence: 64%

Evaluated Kinetics of Terminal and Non-Terminal Addition of Hydrogen Atoms to 1-Alkenes: A Shock Tube Study of H + 1-Butene

Manion

Awan

2015

J. Phys. Chem. A

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Single-pulse shock tube methods have been used to thermally generate hydrogen atoms and investigate the kinetics of their addition reactions with 1-butene at temperatures of 880 to 1120 K and pressures of 145 to 245 kPa. Rate parameters for the unimolecular decomposition of 1-butene are also reported. Addition of H atoms to the π bond of 1-butene results in displacement of either methyl or ethyl depending on whether addition occurs at the terminal or nonterminal position. Postshock monitoring of the initial alkene products has been used to determine the relative and absolute reaction rates. Absolute rate constants have been derived relative to the reference reaction of displacement of methyl from 1,3,5-trimethylbenzene (135TMB). With k(H + 135TMB → m-xylene + CH3) = 6.7 × 10(13) exp(-3255/T) cm(3) mol(-1) s(-1), we find the following: k(H + 1-butene → propene + CH3) = k10 = 3.93 × 10(13) exp(-1152 K/T) cm(3) mol(-1) s(-1), [880-1120 K; 145-245 kPa]; k(H + 1-butene → ethene + C2H5) = k11 = 3.44 × 10(13) exp(-1971 K/T) cm(3) mol(-1) s(-1), [971-1120 K; 145-245 kPa]; k10/k11 = 10((0.058±0.059)) exp [(818 ± 141) K/T), 971-1120 K. Uncertainties (2σ) in the absolute rate constants are about a factor of 1.5, while the relative rate constants should be accurate to within ±15%. The displacement rate constants are shown to be very close to the high pressure limiting rate constants for addition of H, and the present measurements are the first direct determination of the branching ratio for 1-olefins at high temperatures. At 1000 K, addition to the terminal site is favored over the nonterminal position by a factor of 2.59 ± 0.39, where the uncertainty is 2σ and includes possible systematic errors. Combining the present results with evaluated data from the literature pertaining to temperatures of <440 K leads us to recommend the following: k∞(H + 1-butene → 2-butyl) = 1.05 × 10(9)T(1.40) exp(-366/T) cm(3) mol(-1) s(-1), [220-2000 K]; k∞(H + 1-butene → 1-butyl) = 9.02 × 10(8)T(1.40) exp(-1162/T) cm(3) mol(-1) s(-1) [220-2000 K]. Analogous rate constants for other unbranched 1-olefins should be very similar. Despite this, a factor of three discrepancy in the branching ratio for terminal and nonterminal addition is noted when comparing the present values with recommendations from a recent model of the important H + propene reaction. This difference is suggested to be well outside of the possible experimental errors of the present study or the expected differences with 1-butene. There thus appear to be inconsistencies in the current model for propene. In particular the addition branching ratio from that model should not be used as a reference value in extrapolations to other systems via rate rules or automated mechanism generation techniques.

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Section: Introductionmentioning

confidence: 64%

Evaluated Kinetics of Terminal and Non-Terminal Addition of Hydrogen Atoms to 1-Alkenes: A Shock Tube Study of H + 1-Butene

Manion

Awan

2015

J. Phys. Chem. A

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“…For instance, alkene hydrocarbons comprise up to 20% in gasoline . Alkenyl radicals are also present in cyclic alkane combustion in large amounts via opening ring reactions . Unimolecular decomposition of alkenyl radicals typically involves two common reaction categories, i.e., isomerization and dissociation .…”

Section: Introductionmentioning

confidence: 99%

“…Despite the significant role of alkenyl decomposition in the chemical mechanisms of both alkenes and alkanes combustion, previous kinetic studies on alkenyl radicals seem to be limited, especially on long‐chain alkenyl radicals. Awan et al studied the β‐C‐C scission and isomerization (interconversion with cyclopenty) of pent‐1‐en‐5‐yl by shock tube; they also predicted the high‐pressure limit (HPL) rate constants by Rice–Ramsperger–Kassel–Marcus (RRKM)/Master Equation calculations . Tsang and Cheng et al investigated the decomposition of pent‐1‐enyl radicals, assuming that the dissociation channels are dominant.…”

Section: Introductionmentioning

confidence: 99%

Unimolecular Reaction Properties for the Long‐Chain Alkenyl Radicals

Bian

Wang

Zhang

et al. 2015

Int J of Chemical Kinetics

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Although alkenyl radicals are important intermediates involved in both alkanes and alkenes combustion, previous kinetic studies on them are very limited, especially for the long‐chain alkenyl radicals. To deeply investigate unimolecular reaction activities of long‐chain alkenyl radicals, a series of octenyl (C8H15) radicals were chosen to study the reaction kinetics of three typical types of reactions (i.e., intramolecular radical addition, internal H‐migration, and bond dissociation) in this work. The CBS‐QB3 method was used to build potential energy surfaces for these reactions, and the transition state theory was applied to obtain the high‐pressure limit rate constants. Some general rules are observed from our systematic calculations in respect of structure–activity relationships.

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“…The present analysis assumes that relative rates and branching ratios can be experimentally measured with much higher accuracy than one can determine the absolute rate constants. While measurements must be assessed on a case‐by‐case basis, this is the usual situation for experiments that establish direct competitions and follow distinct products with an accurate analytical technique: In work from this laboratory, for example, uncertainties of around 10% (2σ) in relative values are common , and such results are not dissimilar to measurements reported elsewhere in the literature . In contrast.…”

Section: Resultsmentioning

confidence: 99%

The Importance of Relative Reaction Rates in the Optimization of Detailed Kinetic Models

Manion

McGivern

2016

Int J of Chemical Kinetics

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Numerous mathematical tools intended to adjust rate constants employed in complex detailed kinetic models to make them consistent with multiple sets of experimental data have been reported in the literature. Application of such model optimization methods typically begins with the assignment of uncertainties in the absolute rate constants in a starting model, followed by variation of the rate constants within these uncertainty bounds to tune rate parameters to match model outputs to experimental observations. The present work examines the impact of including information on relative reaction rates in the optimization strategy, which is not typically done in current implementations. It is shown that where such rate constant data are available, the available parameter space changes dramatically due to the correlations inherent in such measurements. Relative rate constants are typically measured with greater relative accuracy than corresponding absolute rate constant measurements. This greater accuracy further reduces the available parameter space, which significantly affects the uncertainty in the model outcomes as a result of kinetic parameter uncertainties. We demonstrate this effect by considering a simple example case emulating an ignition event and show that use of relative rate measurements leads to a significantly smaller uncertainty in the output ignition delay time in comparison with results based on absolute measurements. This is true even though the same range of absolute rate constants is sampled in each case. Implications of the results with respect to the maintenance of physically realistic kinetics in optimized models are discussed, and suggestions are made for the path forward in the refinement of detailed kinetic models. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. Int J Chem Kinet 48: [358][359][360][361][362][363][364][365][366] 2016

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Shock tube study of the decomposition of cyclopentyl radicals

Cited by 22 publications

References 28 publications

Evaluated Kinetics of Terminal and Non-Terminal Addition of Hydrogen Atoms to 1-Alkenes: A Shock Tube Study of H + 1-Butene

Evaluated Kinetics of Terminal and Non-Terminal Addition of Hydrogen Atoms to 1-Alkenes: A Shock Tube Study of H + 1-Butene

Unimolecular Reaction Properties for the Long‐Chain Alkenyl Radicals

The Importance of Relative Reaction Rates in the Optimization of Detailed Kinetic Models

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