Inhibition of the hydrogen+oxygen reaction by ethylene. Part 2.—Discussion and evaluation of velocity constants

Abstract

The preceding paper has presented the results obtained from a study of the inhibition of the H₂+O₂ reaction by C₂H₄. The variation in inhibition efficiency with pressure has been attributed to an increasing probability that as the pressure is lowered, the C₂H₅ radicals, formed in the primary inhibition process by the addition of H atoms, react further to propagate the chain. In the present paper the possibility that the “hot” C₂H₅ radicals propagate the chain through OH radicals is eliminated. The variation in inhibition efficiency is shown to arise from a competition between the dissociation of the “hot” C₂H₅ radicals, to form H and C₂H₄, and their stabilization by collisional deactivation. The finite efficiency of C₂H₄, even at zero pressure, is due to the removal of H and OH radicals from the system by abstraction reactions with C₂H₄, which become increasingly important as the pressure is reduced. The following velocity constants have been obtained at 813°K. H+C₂H₄= C₂H^*₅, 3.5×10⁹ l. mole^–1 sec^–1, C₂H^*₅= H+C₂H₄, 3.3×10⁸ sec^–1, H+C₂H₄= H₂+C₂H₃, 2.5×10⁸ l. mole^–1 sec^–1, OH+C₂H₄= H₂O+C₂H₃, 1.1×10¹⁰ l. mole^–1 sec^–1.