Shock wave studies of the reactions HO+H2O2→H2O+HO2 and HO+HO2→H2O+O2 between 930 and 1680 K

Monitoring resonance absorption at the Q1(4) line near 308.4 nm, HO concentration-time profiles were recorded during the thermal decomposition of H2O2 in shock waves between 930 and 1680 K. The results were analyzed with respect to the reactions HO+H2O2→H2O+HO2 (2) and HO+HO2→H2O+O2 (3). Above 800 K, reaction (2) shows a strong increase of the rate constant with temperature. Over the range 240≤T≤1700 K the apparent rate constant is represented as k2=[1.7⋅1018⋅exp(−14 800 K/T)+2.0⋅1012 exp (−215 K/T)] cm3 mol−1 s−1. The rate constant k3 decreases from a value of 2.0⋅1013 at 1100 K to a minimum value of 1.1⋅1013 at 1250 K, and rises again to a value of 4.5⋅1013 cm3 mol−1 s−1 at 1600 K. The anomalous temperature dependences of k2 and k3 suggest mechanisms involving intermediate complex formation.