Reactions forming electronically-excited free radicals. Part 2.—Formation of N4S, N2D and N2P atoms in the H + NF2reaction, and N atom reactions

Abstract

The kinetics of reactions (at 298 K) involving ground-state N ⁴S and excited-state N ²D, ²P atoms have been studied using resonance-fluorescence detection in a discharge-flow system. The N ⁴S+ NO reaction has been studied as a reference reaction: N ⁴S+ NO [graphic omitted] N₂+ O; k₁=(3.4 ± 0.3)× 10^–11 cm³ molecule^–1 s^–1(1σ). Also, the rate constant k₂ for the N ⁴S+ NF₂ reaction has been determined: N ⁴S+ NF₂ [graphic omitted] 2 NF; k₂=(4.6 ± 0.3)× 10^–12 cm³ molecule^–1 s^–1(1σ). The reaction H ²S+ NF₂ gives NF radicals in the a¹Δ state with a branching ratio 0.9: H ²S+ NF₂→ NF a¹Δ+ HF X¹∑⁺. This conclusion is drawn from a study of concentration profiles of N ⁴S and N ²D atoms in the state-selective reactions (4a), (4b): H ²S+ NF a¹Δ→ N ²D+ HF X¹∑⁺(4a), H ²S+ NF X³∑^–→ N ⁴S+ HF X¹∑⁺.(4b)., Although N ²D atoms are an initial product of the H + NF reaction. N ⁴S atoms are formed only at longer reaction times when [N ²D] has mostly decayed. Thus, it is inferred that NF X³∑^– is not a major initial product of the H + NF₂ reaction. Chemiluminescence is emitted in the H + NF₂ reaction from excited NF a¹Δ, b¹∑⁺ and from excited N₂B³Π_g and N₂a¹Π_g in the First Positive (B–A) and Lyman–Birge–Hopfield (a–X) band systems. The precursor of NH chemiluminescence in the H + NF₂ system is thought to be ground-state NH X³∑^– formed in the reaction N ²D+ H₂→ NH X³∑^–+ H.