Catalysis of radical recombination in flames by iron

Flame photometric measurements of H and OH radical concentrations in fuel-rich laminar atmospheric-pressure H2/O2/N2 flames with and without added iron have been made by the Li/Na comparison method. The observed catalysis of radical recombination by iron is quantitatively interpreted in terms of the following homogeneous gas-phase reaction cycle, with associated forward and backward rate coefficients in milliliter · molecule · second units: FeOH + H⇌FeO + H2:kf = 5 × 10−11 exp(−800/T),kb = 1.1 × 10−9 exp(−6200/T);FeO + H2O⇌Fe(OH)2:kf = 9 × 10−12,kb = 1.0 × 1013 exp(−35 500/T);Fe(OH)2 + H⇌FeOH + H2O:kf = 1.1 × 10−10 exp(−300/T),kb = 1.1 × 10−11 exp(−12 000/T). The interpretation also includes contributions from the effectively balanced reaction Fe+H2O⇄FeOH+H; equilibrium constant = 66 exp(−16 100/T).