Direct study of the reactions of vinyl radicals with hydrogen and oxygen atoms

Abstract

The reactions of vinyl radicals with hydrogen and oxygen atoms have been studied at low pressures (0.3–4 mbar) and temperature (293 K) using fast discharge flow reactors and a Laval nozzle reactor. Samples were withdrawn continuously by molecular beam sampling and the stable and labile species were determined by mass spectrometers. Specific detection was obtained either by a mass spectrometer with electron impact ionization (4.5–29.5 eV, 70 eV) and/or high resolution or by a time-of-flight mass spectrometer with multiphoton ionization and/or electron impact ionization. A high detection sensitivity was achieved using modulation techniques, single ion counting and signal averaging. Vinyl radicals were produced via the reaction (1a) C2H4+F→C2H3+HF(1a)→C2H3F+H(1b) The relative rate constants of the radical + atom reactions were measured using the reactions H and O+neo−C5H11 as the standard. This leads to C2H3+H→products(2)k2=(3±2)x1013cm3/mols and for C2H3+O→products(5)k5=(3±2)x1013cm3/mols The mechanisms were found to be C2H3+H→C2H2+H2(2) and C2H3+O→CH3+CO(5a)→CH2CO+H(5b)