A theoretical study on mechanism and kinetics of the C2H3 + C2H3 recombination and the isomerization and dissociation of butadiene

Abstract

Kinetics and mechanism of the C 2 H 3 + C 2 H 3 recombination and the related isomerization–decomposition of C 4 H 6 have been performed utilizing the CCSD(T)/CBS//M06-2X/aug-cc-pVTZ level of theory together with statistical theoretical VRC-TST and RRKM master equation calculations. The potential energy surface describing the C 2 H 3 + C 2 H 3 reaction was established in detail. The evaluated total high-pressure-limit (HPL) rate constant for the entrance C 2 H 3 + C 2 H 3 → 1,3-butadiene reaction, 0.169 × 10 −10 T −0.508 cm 3 /molecule/s, agrees closely within 0.1 to ~ 2% with the experimental data given by Kawano and co-workers, 0.163 × 10 −10 T −0.5 cm 3 /molecule/s, and the HPL rate constant of the CH 2 CCH + CH 3 → C 4 H 6 reaction can be represented by the expression of 8.51 × 10 −11 exp(165.87 cal.mol −1 /RT) cm 3 /molecule/s, in good agreement with the expression of 6.8 × 10 −11 exp(258.3 cal.mol −1 /RT) cm 3 /molecule/s given by Knyazev and Slagleare, while the HPL rate constants for C 4 H 6 → C 4 H 5 + H presented by the Arrhenius expressions k a = 0.165 × 10 15 exp(-84 kcal mol −1 /RT), k b = 0.62 × 10 15 exp(-85.8 kcal.mol −1 /RT), k c = 0.62 × 10 15 exp(−90.2 kcal.mol −1 /RT), and k d = 0.2 × 10 16 exp(−99.1 kcal.mol −1 /RT) s −1 , are in reasonable accordance with the expressions reported by Hidaka et al. and Leung and Lindstedt, being k a,expt. = 0.5 × 10 15 exp(−87.3 kcal mol −1 /RT), k b,expt. = 0.7 × 10 15 exp(−86 kcal.mol −1 /RT), k c,expt. = 0.42 × 10 16 exp(−92.6 kcal.mol −1 /RT), and k d,expt. = 0.14 × 10 16 exp(−98 kcal.mol −1 /RT) s −1 , respectively. Bimolecular rate coefficients for 16 channels on the PES were calculated at various pressures from 7.6 to 76000 Torr and 300 ≤ T ≤ 2000 K, which rapidly increase with rising temperatures and slightly decrease with rising pressures. The predicted rate constants and the product yields of the C 4 H 6 dissociation reaction are in reasonably satisfactory agreement with the previous theoretical and experimental data without any adjustment from the quantum-chemical calculations. The recommended temperature-/pressure-dependent rate constants can be confidently utilized for modeling C 2 H 3 -related systems under atmospheric and combustion conditions.