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

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 k_I=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 k_app≡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 k_V= (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.