Elementary reactions in the oxidation of ethylene: The reaction of OH radicals with ethylene and the reaction of C 2H 4OH radicals with H atoms

Abstract

The reactions of OH+C 2 H 4 and C 2 H 4 OH+H have been studied at low temperatures(around 295 K) and low pressures (0.1–2 torr) using discharge flow reactors and a Laval nozzle reactor. Quantitative product analysis was performed by mass spectrometry (high resolution, ionization curve) combined with molecular beam sampling and synchronous ion counting techniques. The measurements at low pressure and temperature establish the reaction mechanism: OH+C 2 H 4 →C 2 H 4 OH * M →C 2 H 4 OH →HCHO+CH 3 →CH 3 CHO+H By direct calibration procedures the branching ratio at (295 K, 2 torr) was determined (M):(1):(2)=21:44:35 The abstraction reaction OH+C 2 H 4 →H 2 O+C 2 H 3 was found to be negligible ( The mechanism is analyzed in terms of complex formation/stabilization/isomerization/complexdecomposition using unimolecular rate theory. The deduced parameters (energy barrier, frequency ratio) are used to predict product distributions at atmospheric pressure for temperatures up to 1500 K. The measurement of the primary products at low pressures ( 2 H 4 OH+H→H 2 +C 2 H 4 O The rate of reaction (4) was measured relative to the reference reaction C 2 H 5 +H→products leading to k 4 ∼=5 10 13 cm 3 /mol s.