Rate constants for hydrogen + oxygen system, and for H atoms and OH radicals + alkanes

Abstract

Rate constants at 500°C for the elementary steps in the H₂+ O₂ reaction have been revised to take into account self-heating of the reaction mixtures, reaction of O atoms with H₂O₂, and other refinements in the mechanism. By combination with independent data at lower temperatures, Arrhenius parameters for the reactions have been obtained.

Rate constants for OH + RH [reaction (21)] and H + RH [reaction (22)] for C₂–C₅ alkanes have been revised to allow for self-heating, and for reaction of O atoms and HO₂ radicals with the additive. Combination with data at lower temperatures has given Arrhenius parameters for the reactions. The results indicate that, to a first approximation, rate constants for an unknown alkane can be obtained by the relationships k₂₁/k₁= 0.214n_p exp (1070/T)+0.173n_s exp (1820/T)+0.273n_t exp (2060/T)k22 = 2.2 × 10¹⁰n_p exp (–4715/T)+4.9 × 10¹⁰n_s exp (–4005/T)+5.1 × 10¹⁰n_t exp (–3030/T), where n_p, n_sn_t are the number of primary, secondary and tertiary C—H bonds, and k₁ is the rate constant for the reaction OH + H₂= H₂O + H(1).