Shock tube studies on the high temperature chemical kinetics of allyl radicals: reactions with C₂H₂, CH₄, H₂ and C₃H₅ at 1000–1400 K

Abstract

Rate constants of various allyl radical reactions have been measured at combustion relevant temperatures of 1000 to 1400 K. Time resolved absorption spectroscopy was used under reflected shock wave conditions in highly diluted mixtures of the reagents in argon. Studies on the thermal dissociation of 1,5-hexadiene as a precursor reaction of allyl radicals showed pressure dependence between 0.35 and 14 bar with temperature dependent approach of the high pressure limit. Very weak temperature dependence for the C₃H₅ + C₃H₅ combination is established and thermal dissoziations rates of allyl itself were measured above 1170 K. Experimental rate constant for the C₃H₅ + H₂ and C₃H₅ + CH₄ abstraction reactions are reported first time. The important reaction of allyl with acetylene was now measured directly in a combustion relevant temperature range, 1060-1320 K, resulting in k=10^(13.6±6.5) exp [−(90±10) kJ mol⁻¹ /RT] cm³ mol⁻¹ s⁻¹. Branching between two product channels occurs with 95 % towards C₅H₆ + H. Absolute high temperature UV absorption spectra are reported for allyl and cyclopentadiene.