ABSOLUTE RATE MEASUREMENTS OF O-ATOM REACTIONS WITH ETHYLENE AND WITH BUTANE

Abstract

The absolute rate constants for the primary reactions of O-atoms with ethylene and with butane have been determined in a fast-flow system. The O-atoms were produced by electrodeless discharge of O₂ and allowed to react with the hydrocarbon introduced downstream. Addition of a small amount of NO to the gas stream enabled a photometric monitoring of the O-atoms in the reaction zone. The initial atom concentration was determined by NO₂ titration. The reaction could be stopped at any point in the reaction zone by means of a movable surface of cobalt oxide. The hydrocarbon concentration at any point could then be determined by condensation downstream and analysis of the products.Rate measurements were carried out over the temperature range −50° to 200 °C. The rates were found to be consistent with a two-body mechanism. For O-atoms with ethylene, k = 1.8(±0.6) × 10⁻¹¹e^−1600/RT cm³ molecule⁻¹ sec⁻¹ and for O-atoms with butane, k = 5.0(±1.6) × 10⁻¹¹e^−4200/RT cm³ molecule⁻¹ sec⁻¹.