High‐temperature dissociation of ethyl radicals and ethyl iodide

Abstract

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.

A Hierarchical and Comparative Kinetic Modeling Study of C1 − C2 Hydrocarbon and Oxygenated Fuels

“…Recently, Yang and Tranter performed a high‐temperature study of ethyl iodide and ethyl radical decomposition behind incident shock conditions of 55 and 123 Torr and in the temperature range of 1150 − 1870 K. The results of their study were in very good agreement with the calculations of Miller and Klippenstein at 123 Torr and between 10% and 20% lower at the lower pressure.…”

Kinetic Analysis of Ethyl Iodide Pyrolysis Based on Shock Tube Measurements

“…Figure shows the C 2 H 5 I decomposition branching ratio, k R1 /( k R1 + k R3 ), from our optimized rate parameters. This branching ratio is 0.936 at 900 K, decreasing nearly linearly to 0.834 at 1400 K. The extrapolated branching ratio is 0.738 at 2000 K. Kumaran et al suggested a branching ratio of 0.87 ± 0.11 for the temperature range 950−2050 K. Yang and Tranter accepted this ratio but noted that their experimental data could also be reproduced with any branching ratio higher than 0.87 (cf. the caption of Fig.…”

“…The dashed lines show the 3 σ uncertainty limits. The shaded areas show the uncertainty ranges of the reported branching ratios in the corresponding temperature region: (1) 0.92 ± 0.06, Miyoshi et al ( p = 0.6–1.9 bar); (2) higher than 0.87, Yang and Tranter ( p = 0.07–0.16 bar); (3) 0.87 ± 0.11, Kumaran et al ( p = 0.1–0.7 bar); and (4) 0.7 ± 0.1, Weber et al ( p = 1.5 bar).…”

“…Some data were originally obtained for the rate coefficient of the reverse reaction, and these data were transformed to the forward rate coefficient using the thermodynamic data. For reactions (R1) and (R3), the data of Yang and Tranter [19] correspond to their rate coefficient expression extrapolated to infinite pressure (see the rate expression at the bottom of p. 439 in [19]). Yang and Tranter [19] determined the sum of the rate coefficients of reactions (R1) and (R3) in the temperature range of 1150−1870 K and calculated the individual (R1) and (R3) rate coefficients using a temperature independent branching ratio of 0.87, which had been suggested by Kumaran et al [20] For reaction (R5), our uncertainty region has an hourglass shape, which means that our rate coefficient has low uncertainty near 1000 K and rapidly increasing uncertainty toward both higher and lower temperatures.…”

Analytical challenges in the quantitative determination of 2H/1H ratios of methyl iodide

“…In the case of methyl iodide we expect the pyrolysis reaction mechanisms to include C−I bond fission reactions, which may proceed as: as well as through molecular elimination of HI: …”