Average collisional vibrational energy transfer quantities. The exponential model

Tardy, D. C.; Rabinovitch, B. S.

doi:10.1021/j100278a045

Cited by 11 publications

(2 citation statements)

References 7 publications

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“…Collisional energy transfer in our model is treated with a standard exponential-down model, − with energy transfer values selected to fit the experimental results as discussed later. Within the context of RRKM theory, molecules have been treated as symmetric tops.…”

Section: Resultsmentioning

confidence: 99%

Pressure Dependence and Branching Ratios in the Decomposition of 1-Pentyl Radicals: Shock Tube Experiments and Master Equation Modeling

2012

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The decomposition and intramolecular H-transfer isomerization reactions of the 1-pentyl radical have been studied at temperatures of 880 to 1055 K and pressures of 80 to 680 kPa using the single pulse shock tube technique and additionally investigated with quantum chemical methods. The 1-pentyl radical was generated by shock heating dilute mixtures of 1-iodopentane and the stable products of its decomposition have been observed by postshock gas chromatographic analysis. Ethene and propene are the main olefin products and account for >97% of the carbon balance from 1-pentyl. Also produced are very small amounts of (E)-2-pentene, (Z)-2-pentene, and 1-butene. The ethene/propene product ratio is pressure dependent and varies from about 3 to 5 over the range of temperatures and pressures studied. Formation of ethene and propene can be related to the concentrations of 1-pentyl and 2-pentyl radicals in the system and the relative rates of five-center intramolecular H-transfer reactions and β C-C bond scissions. The 3-pentyl radical, formed via a four-center intramolecular H transfer, leads to 1-butene and plays only a very minor role in the system. The observed (E/Z)-2-pentenes can arise from a small amount of beta C-H bond scission in the 2-pentyl radical. The current experimental and computational results are considered in conjunction with relevant literature data from lower temperatures to develop a consistent kinetics model that reproduces the observed branching ratios and pressure effects. The present experimental results provide the first available data on the pressure dependence of the olefin product branching ratio for alkyl radical decomposition at high temperatures and require a value of <ΔE(down)(1000 K)> = (675 ± 100) cm(-1) for the average energy transferred in deactivating collisions in an argon bath gas when an exponential-down model is employed. High pressure rate expressions for the relevant H-transfer reactions and β bond scissions are derived and a Rice Ramsberger Kassel Marcus/Master Equation (RRKM/ME) analysis has been performed and used to extrapolate the data to temperatures between 700 and 1900 K and pressures of 10 to 1 × 10(5) kPa.

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Section: Resultsmentioning

confidence: 99%

Pressure Dependence and Branching Ratios in the Decomposition of 1-Pentyl Radicals: Shock Tube Experiments and Master Equation Modeling

2012

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“…Collisional energy transfer with the argon bath gas has been treated with a standard exponential-down model − with α = 0.293 T cm −1 , where α is the usual parameter that relates to the average energy transferred in deactivating collisions and T is the temperature in kelvin. In our analysis of the decomposition of n -hexyl radicals, we found it necessary to consider tunneling in order to fit both our shock tube results and data on the isomerization reaction from studies at lower temperatures.…”

Section: Resultsmentioning

confidence: 99%

Decomposition and Isomerization of 5-Methylhex-1-yl Radical

et al. 2010

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The decomposition and isomerization reactions of the 5-methylhex-1-yl radical (1-5MeH) have been studied at temperatures of 889-1064 K and pressures of 1.6-2.2 bar using the single pulse shock tube technique. The radical of interest was generated by shock heating dilute mixtures of 5-methylhexyl iodide to break the weak C-I bond, and the kinetics and reaction mechanism deduced on the basis of the olefin cracking pattern observed by gas chromatographic analysis of the products. In order of decreasing molar yields, alkene products from 1-5MeH decomposition are ethene, isobutene, propene, 3-methylbut-1-ene, but-1-ene, E/Z-hex-2-ene, 4-methylpent-1-ene, and hex-1-ene. The first three products account for almost 90% of the carbon balance. The mechanism involves reversible intramolecular H-transfer reactions that lead to the formation of the radicals 5-methylhex-5-yl (5-5MeH), 5-methylhex-2-yl (2-5MeH), 5-methylhex-4-yl (4-5MeH), 5-methylhex-6-yl (6-5MeH), and 5-methylhex-3-yl (3-5MeH). Competitive with isomerization reactions are decompositions by beta C-C bond scission. The main product forming radical is 5-5MeH, which is formed by intramolecular abstraction of the lone tertiary H in the radical. This reaction is deduced to be a factor of 4.0 +/- 0.7 faster on a per hydrogen basis than the analogous abstraction of a secondary hydrogen in 1-hexyl radical. The estimated uncertainty corresponds to 1 standard deviation. The following relative rates have been deduced under our reaction conditions: k(4-5MeH --> C(2)H(5) + 3-methylbut-1-ene)/k(4-5MeH --> CH(3) + Z-hex-2-ene) = 10((0.39+/-0.12)) exp[(675 +/- 270)K/T]; k(4-5MeH --> C(2)H(5) + 3-methylbut-1-ene)/k(4-5MeH --> CH(3) + E-hex-2-ene) = 10((-0.10+/-0.09)) exp[(1125 +/- 210)K/T]; k(3-5MeH --> iso-C(3)H(7) + but-1-ene)/(k)(3-5MeH --> CH(3) + 4-methylpent-1-ene) = 10((0.26+/-0.55)) exp[(1720 +/- 1300)K/T]. Observed olefin distributions depend on the relative rate constants and the interplay of chemical activation and falloff behavior as the energy distributions of the various radicals relax to steady-state values. A kinetic model using an RRKM/master equation analysis has been developed, and absolute rate expressions have been deduced. The model was used to extrapolate the data to temperatures between 500 and 1900 K and pressures of 0.1-1000 bar, and results for 12 isomerization reactions and 10 beta C-C bond scission reactions are reported.

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The energy dependence of 〈ΔE〉, the average energy transferred per collision

Forst¹

1989

Chemical Physics

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Average collisional vibrational energy transfer quantities. The exponential model

Cited by 11 publications

References 7 publications

Pressure Dependence and Branching Ratios in the Decomposition of 1-Pentyl Radicals: Shock Tube Experiments and Master Equation Modeling

Pressure Dependence and Branching Ratios in the Decomposition of 1-Pentyl Radicals: Shock Tube Experiments and Master Equation Modeling

Decomposition and Isomerization of 5-Methylhex-1-yl Radical

The energy dependence of 〈ΔE〉, the average energy transferred per collision

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