Transient oxygen atom yields in H2?O2 ignition and the rate coefficient for O + H2 ? OH + H

Time-resolved measurements of the oxygen atom concentration during shock-wave initiated combustion of low-density (25 ≤ p ≤ 175 kPa) H2O2COCO2Ar mixtures have been made by monitoring CO + O → CO2 + hv (3 to 4 eV) emission intensity, calibrated against partial equilibrium conditions attained promptly at H2:O2 = 1. Significant transient excursions (“spikes”) of [O] above constant-mole-number partial-equilibrium levels were found from 1400 to 2000°K for initial H2:O2 ratios of 16 and 10 and below ± 1780°K for H2:O2 = 6; they did not occur in this range for H2:O2 ± 4. Numerical treatment of the H2O2CO ignition mechanism for our conditions showed [O] to follow a steady-state trajectory governed by large production and consumption rates from the reactions with a pronounced maximum in the production term ka[H][O2]. The measured spike concentration data determine kb/ka = 3.6 ± 20%, independent of temperature over 1400 ≤ T ≤ 1900°K, which with well-established ka data yields This result reinforces the higher of several recent combustion-temperature determinations, and its correlation with results below 1000°K produces a distinctly concave upward Arrhenius plot which is closely matched by BEBO transition state calculations.