Flow tube studies of the C(3P) reactions with ethylene and propylene

Abstract

Product detection studies of C(³P) atom reactions with ethylene, C₂H₄(X¹A_g) and propylene, C₃H₆(X¹A′) are carried out in a flow tube reactor at 332 K and 4 Torr (553.3 Pa) under multiple collision conditions. Ground state carbon atoms are generated by 193 nm laser photolysis of carbon suboxide, C₃O₂ in a buffer of helium. Thermalized reaction products are detected using tunable VUV photoionization and time of flight mass spectrometry. For C(³P) + ethylene, propargyl (C₃H₃) is detected as the only molecular product in agreement with previous studies on this reaction. The temporal profiles of the detected ions are used to discriminate C(³P) reaction products from side reaction products. For C(³P) + propylene, two reaction channels are identified through the detection of methyl (CH₃) and propargyl (C₃H₃) radicals for the first channel and C₄H₅ for the second one. Franck–Condon Factor simulations are employed to infer the C₄H₅-isomer distribution. The measured 1 : 4 ratio for the i-C₄H₅ isomer relative to the methylpropargyl isomers is similar to the C₄H₅ isomer distribution observed in low-pressure flames and differs from crossed molecular beams data. The accuracy of these isomer distributions is discussed in view of large uncertainties on the photoionization spectra of the pure C₄H₅ isomers.