Reactions of NH Radicals. 6. Reactions of NH(a1Δ) with C2H2 and Unimolecular Decompositions of C2H3N*

Article abstract of DOI:10.1021/j100328a038

Photolysis of HN3 vapor in the presence of C2H2 was studied at 313nm and 303 K.The products were N2, H2, CH4, C2H4, C2H6, NH4N3, C4H5N*HN3 (salt of C4H5N with HN3), HCN, CH3CN, and polymers.From the quantum yields of these products, measured as a function of the pressure of C2H2 or HN3, the following mechanism for the main reactions was inferred: HN3 + hν(313 nm) -> NH(a¹Δ) + N2; NH(a¹Δ) + HN3 -> 2N2 + 2H (2a); NH(a¹Δ) + HN3 -> NH2 + N3 (2b); NH(a¹Δ) + HN3 -> N2 + N2H2^* (2c); NH(a¹Δ) + C2H2 -> C2H3N^* (CH=CH-NH and CH(*)C-NH2) (3); C2H3N^* -> CH3 + CN (4); C2H3N^* -> H + C2H2N (5); C2H3N^* -> C2H + NH2 (6).The rate constant ratios at 303 K are k₃/k₂ = 1.2_o, k₅/k₄ = 15₇, and k₆/k₄ = 0.82.The efficiency of the insertion to give CH(*)C-NH2 in reaction 3 was about 0.05 of that of the addition to form CH=CH-NH.The spin relaxation of NH(a¹Δ) to NH(X³Σ^-) by C2H2 and the collisional deactivation of C2H3N^* were not found.The rearrangement from CH=CH-NH to CH3NC or CH3CN and the unimolecular decomposition rates by the RRKM theory for reactions 4 and 6 were discussed.The relative and absolute rate constants were compared for the reactions of NH(a¹Δ) with various reactants.