The Application of Densitometric Methods to the Measurement of Rate Processes in Shock Tubes

Kiefer, J. H.

doi:10.1016/b978-012086430-0/50038-5

Cited by 2 publications

(4 citation statements)

References 175 publications

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“…The large positive spike and preceding valley in Fig. 1 are due to passage of the shock front through the laser beam [21]. The flat signal prior to arrival of the incident shock wave in the observation zone is used to establish the baseline for each experiment.…”

Section: Resultsmentioning

confidence: 99%

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High‐temperature dissociation of ethyl radicals and ethyl iodide

Yang

Tranter

2012

Int J of Chemical Kinetics

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The decomposition of ethyl iodide and subsequent dissociation of ethyl radicals have been investigated behind incident shock waves in a diaphragmless shock tube by laserschlieren (LS) densitometry (1150-1870 K, 55 ± 2 Torr and 123 ± 3 Torr). The LS density-gradient profiles were simulated assuming that the initial dissociation of C 2 H 5 I proceeded by 87% C I fission and 13% HI elimination. Excellent agreement was found between the simulations and experimental profiles. Rate coefficients for the C I scission reaction were obtained and show strong falloff. Gorin model RRKM (Rice, Ramsperger, Kassel, and Marcus) calculations are in excellent agreement with the experimental data with E 0 = 55.0 kcal/mol, which is in very good agreement with recent thermochemical measurements and evaluations. However, E 0 is approximately 2.7 kcal/mol higher than previous estimates. First-order rate coefficients for dissociation of C 2 H 5 I were determined to be k 55Torr = 8.65 × 10 68 T −16.65 exp(−37,890/T ) s −1 , k 123Torr = 3.01 × 10 69 T −16.68 exp(−38,430/T ) s −1 , k ∞ = 2.52 × 10 19 T −1.01 exp(−28,775/T ) s −1 . Rates of dissociation for ethyl radicals were also obtained, and these are in very good agreement with theoretical predictions (Miller J. A. and Klippenstein S.

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Section: Resultsmentioning

confidence: 99%

“…The LS diagnostics and technique have also been thoroughly described previously [20,21]. The molar refractivity of Kr = 6.367 [22], whereas that of C 2 H 5 I (24.28), was calculated from its refractive index and molar density.…”

Section: Methodsmentioning

confidence: 99%

High‐temperature dissociation of ethyl radicals and ethyl iodide

Yang

Tranter

2012

Int J of Chemical Kinetics

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“…i.d., whose detailed layout has been very fully described [37]. The ST/LS diagnostics have also been described previously [38]. The data acquisition system for the LS experiment has been upgraded, giving improved sensitivity and resolution, but again this has been fully described elsewhere [39].…”

Section: Experiments the Shock Tubementioning

confidence: 99%

“…For such fast relaxation, an integration of the density gradients with a comparison to thermodynamic calculations is considered essential to assure that the resolved process is indeed a complete relaxation of the vibrational modes. Thus the observed gradients have been integrated over t = 0 → ∞ assuming exponential behavior throughout, giving a net density change [38][39][40]:…”

Section: Relaxationmentioning

confidence: 99%

Shock tube study of 1,3,5‐triazine dissociation and relaxation and relaxation of pyrazine

Kiefer

2010

Int J of Chemical Kinetics

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The three-body dissociation of 1,3,5-triazine (s-triazine, s-C 3 H 3 N 3 → 3HCN) has been observed in incident shock waves with the laser-schlieren technique. The experiments use 5% triazine/Kr and cover 1630-2350 K for 100-600 Torr. These experiments show dissociation rates with strong falloff and a slight but fully expected pressure dependence. The dissociation is without secondary reaction save for a possible, but rather unlikely, contribution from the isomerization HCN → HNC. Electronic structure calculations of the transitionstate properties (G3B3, HL1, E o = 84.6 kcal/mol) are used to construct a Rice-RamspergerKassel-Marcus (RRKM) model whose fit to the rate measurements suggests a E down of 1200 cm −1 . However, a seemingly better fit is achieved using the barrier of 81 kcal/mol proposed by Dyakov et al. (J. Phys. Chem. A 2007, 111, 9591-9599). With this barrier k ∞ (s −1 ) = 5.3 × 10 16 exp(−86.6(kcal/mol)/RT), and the fit now accepts the more routine E down = 126(T /298) 0.9 . It seems the dissociation most likely occurs by a direct, one-step, "triple" dissociation to 3HCN, although the present experiments cannot rule out a multistep process. Vibrational relaxation of the triazine was also examined in 5% and 20% mixtures with Kr over 770-1500 K for pressures between 6 and 14 Torr. Relaxation is very fast, with a slight inverse temperature dependence, P τ rising from 100 to 200 ns-atm over the full temperature range. Integrated gradients are in good accord with calculated total changes in density, indicating a single exponential relaxation. A separate investigation of relaxation in the related molecule pyrazine (500-1300 K, in 1% and 5% in Kr, between 13 and 66 Torr) is included. Again relaxation is rapid, but here the temperature dependence seems more normal, the relaxation times decreasing slightly with temperature. C

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The Application of Densitometric Methods to the Measurement of Rate Processes in Shock Tubes

Cited by 2 publications

References 175 publications

High‐temperature dissociation of ethyl radicals and ethyl iodide

High‐temperature dissociation of ethyl radicals and ethyl iodide

Shock tube study of 1,3,5‐triazine dissociation and relaxation and relaxation of pyrazine

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