High temperature rate coefficient measurements of HÂ +Â O2 chain-branching and chain-terminating reaction

Rate coefficients for H + O2 → OH + O (R1) and H + O2 + M → HO2 + M (R9) were measured via OH absorption behind reflected shock waves, being: k1 = 6.73 × 1015 T−0.50 exp (−8390 K/T)  cm3 mol−1 s−1 at T = 950-3100 K and k9, 0/[Ar] = 5.55 × 1018 T−1.15 cm6 mol−2 s−1 at T = 950-1200 K. Our experimental results for k1 strongly support recent ab initio calculations showing temperature curvature due to back dissociation, HO2 → O + OH following O + OH → HO2 if the reaction is considered from the reverse direction.