REACTION OF ATOMIC OXYGEN WITH SOME SIMPLE ALKENES .1. LOW-PRESSURE STUDIES ON REACTIONS INVOLVING ETHENE, PROPENE AND (E)-BUT-2-ENE

The reaction of atomic oxygen O(P-3) with ethene, propene and (E)-but- 2-ene has been studied between 10 and 50 mbar total pressure using the alkene as both reactant and bath-gas. NO2 was used as the source of a tomic oxygen, and the decay of NO2, which is sensitive to the radical products from the reaction of O atoms with alkenes, was followed by la ser-induced fluorescene. Branching ratios for total radical production were obtained for the propene and (E)-but-2-ene systems. The radical branching ratio for the propene system was observed to decrease with p ressure by a factor of about two over the range measured, falling from 0.64 at 10 mbar to 0.36 at 40 mbar total pressure. The radical branch ing ratio for the (E)-but-P-ene system also decreased by a factor of t wo, failing from a value of 0.22 at 10 mbar to 0.11 at 30 mbar. The re sults for the ethene system were inconclusive, in that only a range fo r the branching ratios for production of CH3 + HCO and H + CH2CHO coul d be obtained. These findings were confirmed by extensive modelling of the results.