Excitation and Quenching of CO Fourth Positive Chemiluminescence Due to Reactions Involving C2O

Vacuum ultraviolet chemiluminescence from photolyzed C₃O₂/O and C₃O₂/NO₂ mixtures has been observed and identified as the CO fourth positive ${\mathrm{(A}}^1{\mathrm{\Pi \; \to \; X}}^1\mathrm{\Sigma )}$ system. Photolysis of C₃O₂ is used as a method of producing ${\mathrm{C}}_2\mathrm{O}{\mathrm{(X̃}}^3\mathrm{\Sigma )}$ molecules in concentrations which are viewed by adjusting the C₃O₂ flow rate or the photolytic flash energy. Microwave dissociation of O₂ and photolysis of NO₂ are used as alternative sources of O(³P) atoms, with equivalent results. The intensity of emission is found to be proportional to the product of the concentrations of O(³P) and photolytically produced C₂O, indicating that the binary reaction ${\mathrm{C}}_2\mathrm{O}+\mathrm{O}{(}^3\mathrm{P)\to }\mathrm{CO*}{\mathrm{(A}}^1\mathrm{\Pi )+}\mathrm{CO}{\mathrm{(X}}^1\mathrm{\Sigma )}$ produces the chemiluminescence. Absolute (300°K) rate constants for the reaction of C₂O with O, and for quenching of the chemiluminescence by NO and O₂, have been obtained by the method of kinetic emission spectroscopy. The data yield an over‐all rate constant for the ${\mathrm{C}}_2\mathrm{O}+\mathrm{O}\text{→ 2\hspace{0.17em}}\mathrm{CO}$ reaction of ${\text{9.5}}_{\text{−3.6}}^{\text{+5.7}}{\text{× 10}}^{\text{−11}}\hspace{0.17em}{\mathrm{cm}}^3\hspace{0.17em}{\mathrm{particle}}^{\text{−1}}·{\sec }^{\text{−1}}$ , and quenching rate constants of ${\text{1.65± 0.35× 10}}^{\text{−12}}$ and ${\text{1.2± 0.2× 10}}^{\text{−10}}\hspace{0.17em}{\mathrm{cm}}^3\hspace{0.17em}{\mathrm{particle}}^{\text{−1}}·{\sec }^{\text{−1}}$ for O₂ and NO, respectively. There is some question concerning whether the quenching effect of NO and O₂ involves a chemical reaction with C₂O or de‐excitation of excited C₂O*. On the basis of the over‐all C₂O rate constant obtained from this experiment and previously published estimates of relative rate of populating various CO* levels, the rate constant for the ${\mathrm{C}}_2\mathrm{O}+\mathrm{O}{(}^3\mathrm{P)\to }\mathrm{CO*}{\mathrm{(A}}^1\mathrm{\Pi )+}\mathrm{CO}{\mathrm{(X}}^1\mathrm{\Sigma )}$ reaction is estimated to be between 10⁻¹¹ and 10⁻¹² cm³ particle⁻¹·sec⁻¹.