Reaction of atomic oxygen with carbon dioxide behind reflected shock waves

The rate constant for O + CO2 → CO + O2 has been measured by monitoring CO2 infrared emission from dilute CO2/N2O/Ar mixtures behind reflected shock waves. Initial temperatures ranged from 3015°K to 4675°K and the total concentrations were 1.3–1.5 × 1018 molecule/cm3. Under these conditions, the CO2 concentration was observed to decay exponentially, and this decay is consistent with the mechanism: N2O + M → N2 + O + M, (1); N2O + O → NO + NO, (2); N2O + O → N2 + O2, (3); O + CO2 → CO + O2, (4); CO2 + M → CO + O + M, (5). Conditions are such that the oxygen atoms produced via (1)–(3) remain at a constant concentration (within 10%) during the time interval when the CO2 decay rate kapp is measured. Methods are described which estimate both the temperature and atomic oxygen concentration during this interval. These estimates then allow k4 to be calculated from kapp and known values for k5. The Arrhenius parameters (in units of cm3 molecule−1 · sec−1) are: log A = −11.1±0.2 and EA = 36.1±2.9 kcal/mole. This value is significantly lower than the previous direct measurement of k4 and is reasonably consistent with high temperature data on k−4.