A high temperature chemical kinetics study of the O

The dissociation rate of O2 was measured at very high temperature (3000 K to 4500 K) for pressure between 120 and 450 kPa from atomic oxygen concentration profiles in a shock wave. O concentration was measured using Atomic Resonance Absorption Spectrophotopetry (ARAS) at 130.5 nm. O-ARAS was calibrated by complete and rapid dissociation of N2O in N2+O. Two modified Beer-Lambert expressions were established, each of them was associated to a different detection system. O concentration could be measured between 7.1012 and 3.1014 atoms cm-3. The influence of impurities and residual pressures on the measurements was discussed from simulations with detailed kinetic models. The expression of the rate constant of the dissociation reaction O2+Ar ↦ 2O + Ar is kd (cm3 mol-1 s-1) = 3.4 1014 exp (-55700/T), we deduced the recombination rate kr (cm6 mol-2 s-1) = 4 1013 exp (530/T). These two expressions agree with the ones recommended in recent compilations. The rate constants kd and kr could be estimated with an uncertainty less than 30% in the studied pressure and temperature ranges