Reaction of Atomic Oxygen with Acetylene. II. Chemi-Ionization and Chemiluminescence

The chemiluminescence and chemi‐ionization resulting from the room‐temperature reaction of atomic oxygen with acetylene have been investigated. The absolute intensity of chemiluminescent radiation and the over‐all rate of chemi‐ion formation have been measured and the relative concentrations of various individual chemi‐ions have been observed with a T.O.F. mass spectrometer. It has been shown conclusively from these measurements that chemi‐ionization does not arise primarily from the reactions: $$\begin{array}{c}\mathrm{CH}{\mathrm{\hspace{0.17em}(A}}^2\mathrm{\Delta )+}\mathrm{O}={\mathrm{CHO}}^{+}{\mathrm{+e}}^{-},\\ \mathrm{CH}{\mathrm{\hspace{0.17em}(A}}^2\mathrm{\Delta )+}{\mathrm{C}}_2{\mathrm{H}}_2={\mathrm{C}}_3{\mathrm{H}}_3^{+}{\mathrm{+e}}^{-}.\end{array}$$ It has been shown also that if ionization arises from the reaction $$\mathrm{CH}{\mathrm{\hspace{0.17em}(X}}^2\mathrm{\pi )+}\mathrm{O}={\mathrm{CHO}}^{+}{\mathrm{+e}}^{-},$$ a mechanism that has also received wide support, then the ground state CH (X ²π) molecule must be produced by some mechanism other than that producing CH (A ²Δ). The CH (A ²Δ—X ²π) system was found to be the most intense feature of the chemiluminescent spectrum. Weak emission from the C₂ Swan bands and from the CN violet system was also observed. The intensity of the weak OH emission was found to be consistent with it being produced by reactions with molecular oxygen. The CH emission was shown to arise from a complex series of reactions involving the participation of three molecules of acetylene and two atoms of oxygen. Two possible mechanisms for its production are discussed.