RESUMO
Product detection studies of C((3)P) atom reactions with ethylene, C2H4(X(1)Ag) and propylene, C3H6(X(1)A') 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((3)P) + 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((3)P) reaction products from side reaction products. For C((3)P) + 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.
RESUMO
The reaction of the OH radical with phenylacetylene is studied over the 298-423 K temperature range and 1-7.5 Torr pressure range in a quasi-static reaction cell. The OH radical is generated by 266 nm photolysis of hydrogen peroxide (H2O2) or 355 nm photolysis of nitrous acid (HONO), and its concentration monitored using laser-induced fluorescence. The measured reaction rates are found to strongly depend on laser fluence at 266 nm. The 266 nm absorption cross-section of phenylacetylene is measured to be 1.29 (±0.71) × 10(-17) cm(2), prohibiting any accurate kinetic measurements at this wavelength. The rates are independent of laser fluence at 355 nm with an average value of 8.75 (±0.73) × 10(-11) cm(3) s(-1). The reaction exhibits no pressure or temperature dependence over the studied experimental conditions and is much faster than the estimated values presently used in combustion models. These results are consistent with the formation of a short lifetime intermediate that stabilizes by collisional quenching with the buffer gas. The structures of the most likely formed products are discussed based on both the computed energies for the OH-addition intermediates and previous theoretical investigations on similar chemical systems.
