Chemical CO and CO2 lasers produced from the CH + O2 reaction

Abstract

Strong 5 μm CO laser emission was observed in the flash photolysis (λ≥ 165 nm) of mixtures of O₂ and CHBr₃ in the presence of large amounts of diluent (SF₆, Ar, or He). About 60 vibration‐rotation transitions were identified in the range between Δν = 14→13 and 2→1. The laser intensity was found to vary linearly with flash energy. The effects of various additives (He, Ar, SF₆, CO, N₂, N₂O, and CO₂) were investigated. The stimulated emission is concluded to result primarily from the four‐centered reaction $\mathrm{CH}+{\mathrm{O}}_2\to {\displaystyle {lim}^1}{\mathrm{CO}}^{†}+{\mathrm{OH}}^{†}$ ,${\mathrm{\Delta \; H}}_1^0\text{=−159\hspace{0.17em}}\mathrm{kcal/mole.}$ Other possible minor reactions were also considered. No OH emission was detected under the same experimental conditions. With the aid of a band‐pass filter (8.6–15 μm range), 10 μm CO₂ emission was observed concurrently with the 5 μm CO emission. The CO₂ emission, which consisted of the P(58)–(70) lines of the (001)→(020) band, was found to vary strongly with the partial pressure of O₂. Since both the intensity of this emission and the yield of CO₂ increased linearly with flash energy, the (001) → (020) CO₂ emission is believed to be the direct consequence of the following CH+O₂ reaction: $\mathrm{CH}+{\mathrm{O}}_2\to {\displaystyle {lim}^{10}}\mathrm{H}+{\mathrm{CO}}_2^{†}$ ,${\mathrm{\Delta \; H}}_{10}^0\text{=−184\hspace{0.17em}}\mathrm{kcal/mole.}$ This is the first example of lasing from a chemically produced excited polyatomic molecule. When a small amount of N₂O or CO₂ was added to the O₂–CHBr₃–He mixture, the regular (001)→(100) band of both molecules began to lase at ∼P(18)–P(28), presumably resulting from the energy transfer process OH^†+M(000)→OH+M(001), where M = CO₂ or N₂O.