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摘要
The shock tube technique has been used to study the reactions CH3 + C2H6 -> C2H4 + CH4 + H (1), CH3 + C2H4 Products + H (2), and CH3 + C2H2 -> Products + H (3). Biacetyl, (CH3CO)(2)., was used as a clean high temperature thermal source for CH3-radicals for all the three reactions studied in this work. For reaction 1, the experiments span a T-range of 1153 K <= T <= 1297 K, at P similar to 0.4 bar. The experiments on reaction 2 cover a T-range of 1176 K T 1366 K, at P similar to 1.0 bar, and those on reaction 3 a T-range of 1127 K <= T <= 1346 K, at P similar to 1.0 bar. Reflected shock tube experiments performed on reactions 1-3, monitored the formation of H-atoms with H-atom Atomic Resonance Absorption Spectrometric (ARAS). Fits to the H-atom temporal profiles using an assembled kinetics model were used to make determinations for k(1), k(2), and k(3). In the case of C2H6, the measurements of [HI-atoms were used to derive direct high-temperature rate constants, k(1), that can be represented by the Arrhenius equation k(1)(T) = 5.41 X 10(-12) exp(-6043 KIT) cm(3) molecules(-1) s(-1) (1153 K T 1297 K) for the only bimolecular process that occurs, H-atom abstraction. TST calculations based on ab initio properties calculated at the CCSD(T)/CBS/ /M06-2X/cc-pVTZ level of theory show excellent agreement, within +/- 20%, of the measured rate constants. For the reaction of CH3 with C2H4, the present rate constant results, k(2)', refer to the sum of rate constants, k(2b) + k(2c), from two competing processes, addition elimination, and the direct abstraction CH3 + C2H4 -> C3H6 + H (2b) and CH3 + C2H4 -> C2H2 + H + CH4 (2c). Experimental rate constants for k2' can be represented by the Arrhenius equation k2'(T) = 2.18 X 10(-10) exp(-11830 KIT) cm(3) molecules-1 s-1 (1176 K T 5 1366 K). The present results are in excellent agreement with recent theoretical predictions. The present study provides the only direct measurement for the high-temperature rate constants for these channels. Lastly, measurements of H-atoms from the reaction of CH3 with C2H2 provided direct unambiguous determinations of the rate constant for the dominant process under the present experimental conditions, the addition elimination, CH3 + C2H2 -> p-C3H4 + H (3b). Experimental rate constants for k(3b) can be represented by the Arrhenius equation k3b(T) = 5.16 x 10(-13) exp(-3852 KIT) cm(3) molecules(-1) s(-1) (1127 K T 1346 K). The present determinations for k3b represent the only direct measurements for this reaction and are also in good agreement with recent theoretical predictions. The present experimental k3b values were also used to derive rate constants, k(-3b), for the more extensively studied back-process, the reaction of H-atoms with propyne. The best fit Arrhenius equation, combining the presently derived k(-3b) values with a recent experimental determination for k(-3b), can be represented by k(-3b)(T) = 3. 87 x 10(-11) exp(-1313 K/T) cm(3) molecules(-1) s(-1) (870 K <= T <= 1346 K). The present studies represent a novel implementation of the sensitive H-ARAS technique to measure rate constants for poorly characterized and difficult to isolate "slow" CH3-radical reactions with stable C-2 hydrocarbons.
- 出版日期2013-10-10
