文摘
The reaction between vinyl radical, C2H3, and 1,3-butadiene, 1,3-C4H6, has long been recognized as a potential route to benzene, particularly in 1,3-butadiene flames, but the lack of reliable rate coefficients has hindered assessments of its true contribution. Using laser flash photolysis and visible laser absorbance (位 = 423.2 nm), we measured the overall rate coefficient for C2H3 + 1,3-C4H6, k1, at 297 K 鈮?T 鈮?494 K and 4 鈮?P 鈮?100 Torr. k1 was in the high-pressure limit in this range and could be fit by the simple Arrhenius expression k1 = (1.1 卤 0.2) 脳 10鈥?2 cm3鈥痬olecule鈥? s鈥?鈥痚xp(鈭?.9 卤 0.6 kJ鈥痬ol鈥?/RT). Using photoionization time-of-flight mass spectrometry, we also investigated the products formed. At T 鈮?494 K and P = 25 Torr, we found only C6H9 adduct species, while at 494 K 鈮?T 鈮?700 K and P = 4 Torr, we observed 鈮も埣10% branching to cyclohexadiene in addition to C6H9. Quantum chemistry master-equation calculations using the modified strong collision model indicate that n-C6H9 is the dominant product at low temperature, consistent with our experimental results, and predict the rate coefficient and branching ratios at higher T where chemically activated channels become important. Predictions of k1 are in close agreement with our experimental results, allowing us to recommend the following modified Arrhenius expression in the high-pressure limit from 300 to 2000 K: k1 = 6.5 脳 10鈥?0 cm3鈥痬olecule鈥? s鈥?鈥?i>T2.40鈥痚xp(鈭?.76 kJ鈥痬ol鈥?/RT).