Yields of singlet nitrenes from halogen atom—azide molecule reactions

Chemiluminescence from the a¹Δ and b¹Σ⁺ excited electronic states of nitrogen halide diatomics is observed when HN₃ is allowed to react with mixtures of halogen atoms in a discharge-flow apparatus. Excited NF (a¹Δ) is produced by the F + HN₃ reaction, and NCl (a¹Δ, b¹Σ⁺) and NBr (a¹Δ, b¹Σ⁺) are produced by the F, Cl, + HN₃ and F, Br + HN₃ reactions, respectively. In the low-density limit, the yield of NF(a¹Δ) was found to be near unity. The yields of the b¹Σ⁺ states of NCl and NBr were determined to have a lower limit of ca. 10%. A number of results from these experiments, including direct observation of N₃ radicals in the flow, support a hypothetical mechanism in which N₃ acts as an intermediate. A second possible mechanism proceeding via an HNF intermediate cannot be ruled out.