CO Chemiluminescence from Flames

The chemiluminescence from the reaction of oxygen atoms and carbon suboxide in a flow system has been reinvestigated. In addition to the “triplet” bands reported previously, two other band systems of CO were observed: the Herman bands, also in the red, and the Fourth Positive bands in the vacuum ultraviolet. The three electronic states show a common excitation limit of almost 9 eV above the ground state. The emission intensity in the red and in the vacuum ultraviolet vary together as the flame conditions are changed, showing that the three excited states are formed in a single reaction. Traces of hydrogen are not necessary for the chemiluminescence. The reaction responsible for the emission is probably $\mathrm{O}{(}^3\mathrm{P)\hspace{0.17em}+\hspace{0.17em}}{\mathrm{C}}_2\mathrm{O}{\mathrm{(X}}^3\mathrm{\Sigma )\to }\mathrm{CO}{\mathrm{(A}}^1{\mathrm{\Pi ,\; d}}^3{\mathrm{\Delta ,\; e}}^3\mathrm{\Sigma )\hspace{0.17em}+\hspace{0.17em}}\mathrm{CO}{\mathrm{(X}}^1\mathrm{\Sigma )}$ . Quenching of the CO emission depends on the ratios (NO) / (O) and (O₂) / (O). NO is a more efficient quencher than O₂, in agreement with the behavior found for ${\mathrm{C}}_2\mathrm{O}{\mathrm{(X}}^3\mathrm{\Sigma )}$ formed by the photolysis of C₃O₂. The vacuum‐ultraviolet emission from a O + C₂H₂ flame was found to be identical to that of the O + C₃O₂ flame. As required by the single‐reaction hypothesis, the “triplet” bands and probably the Herman bands were found in the spectrum of the O + C₂H₂ flame. The vacuum‐ultraviolet photon yield from the O + C₂H₂ flame was 10^{−4.3 ± 0.5}/C₂H₂. Possible reactions which could form C₂O in these flames are discussed.