A shock tube study of the recombination of carbon monoxide and oxygen atoms

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Abstract
Time resolved emissions from CO2 and the radiative recombination of CO and O (flame‐band emission) have been monitored in a variety of N2O/CO/Ar mixtures. These mixtures were studied behind reflected shock waves at temperatures between 2100–3200 K and total concentrations between 2.5–7.7×1018 molecule/cm3. The flame‐band detector was calibrated so that absolute concentrations of atomic oxygen could be determined. These data were shown to be consistent with the following mechanism: N2O+M=N2+O+M (I), N2O+O=2NO (II), N2O+O=N2+O2 (III), with kI=4.5×10−10 exp(−226kJ/RT) cm3 molecule−1⋅ s−1 and k2=k3 =7.7×10−11 exp(−117kJ/RT). This combination was also shown to be consistent with earlier data from this laboratory. CO2 was observed to increase linearly with time in these experiments, and an apparent recombination rate constant defined as kapp≡dCO2/dt/([CO] [O] [M]) was measured and found to be a function of pressure. This behavior was attributed to the presence of very small concentrations of hydrogenous impurities. Data at higher pressures were used to estimate the rate constant for the recombination CO+O+M=CO2+M (V) since the effect of impurities was minimized here. It was found that kV= (1.6±0.3) ×10−34 cm6 molecule−2⋅ s−1 between 2100–3200 K. This value is shown to be consistent with recent studies of CO2 dissociation which report ’’normal’’ activation energies.

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