Formation of N2(A3Σu+) and N(2D, 2P) by Photodissociation of HN3 and N2O and Their Reactions with NO and N2O

Abstract

The formation of NO (A ²Σ⁺) and NO (B ²II) in the photolysis of N₂O at 1236 and 1470 Å was investigated by observing the fluorescence of the γ and β bands. The β‐band fluorescence is obtained when pure N₂O is photolyzed at 1236 and 1470 Å in a flow system. The β bands are observed with vibrational excitation up to v′=3. The β bands disappear with the addition of small amounts of NO, whereas the emission of rotationally hot γ bands is obtained. The γ bands are observed with vibrational excitation up to v′=2. According to the energetics, NO (A ²Σ⁺) and NO (B ²II) are formed at 1470 Å as well as at 1236 Å not by direct photodissociation of N₂O but by secondary reactions. No fluorescence is obtained when N₂O or N₂O/NO mixtures are irradiated at wavelengths $\text{≧1600}$ Å, i.e., within the long‐wavelength absorption band of N₂O. The roles of N₂ (A ³Σ_u⁺), N (²D), N (²P) are evaluated and discussed. The emission of γ bands is also obtained in the photolysis of HN₃/NO mixtures at 1470 and 1236 Å. This observation is explained by the photodissociation $${\mathrm{HN}}_3\to {\mathrm{N}}_2{\mathrm{(A\hspace{0.17em}\Sigma }}_u^{+}\mathrm{)+}\mathrm{NH}{\mathrm{(X}}^3{\Sigma }^{-})$$ followed by the reaction between N₂ (A ³Σ_u⁺) and NO, yielding NO (A ²Σ⁺). The other possibility, that O atoms which are formed by photodissociation of NO react with HN₃ to form excited NO—as in the O/N₂H₄ atomic flame—is excluded.