High Temperature Allyl Recombination Kinetics

摘要

The recombination of allyl, C_3H_5, an important long-lived radical, has been studied in a diaphragmless shock tube using laser schlieren densitometry (P_2 = 10, 30, 60, 120 Torr, 800 < T_2 < 1700 K). Allyl was generated both from allyl iodide and 1,5-hexadiene precursors in mixtures of 0.5-4%, dilute in Kr, and excellent agreement was observed using both precursors. The density gradients obtained from the laser schlieren profiles were simulated and fit by a reaction mechanism that included secondary chemistry and was notably sensitive to system thermochemistry. C_3H_5 + C_3H_5 is dominated by recombination to 1,5-C_6H_(10), and this reaction shows significant fall-off. A much smaller fraction, <0.05, proceeds by disproportionation to a-C_3H_4 + C_3H_6. Second order rate coefficients for allyl radical recombination were determined as: k_(1a,124Torr) = (2.6 ± 0.8) × 10~(55) T~(-12.995) exp(-8426/T), k_(1a,57Torr) = (1.7 ± 0.5) × 10~(60) T~(14.49) exp(-9344/T), k_(1a, 30Torr) = (7.5 ± 2.3) × 10~(66) T~(-15.935) exp(-10192/T) cm~3 mol~(-1) s~(-1). This study was extended into higher pressure conditions, (P_5 = 1, 4, 10 atm, 700 < T_5 < 1300 K) in a single pulse shock tube, and excellent agreement throughout the entire pressure/temperature range is observed with our developed RRKM model.