PHOTODISSOCIATION OF NCN3 IN VACUUM-ULTRAVIOLET PRODUCTION OF CN B2SIGMA AND NCN ALPHA32

The photodissociation of NCN3 in the vacuum ultraviolet has yielded CN B 2Σ and NCN A 3II. No NCN 1II was detected. The fluorescence intensity of the CN violet emission, I f/I0 was measured as a function of incident wavelength, λ. The If/I0-vs-λ curve shows structure, indicating that the process NCN3→hv→CN B 2Σ+N3 is predissociative. The yield at 1216 Å is estimated to be approximately 2.5%. The threshold wavelength of incident photons to yield CN B 2Σ is 1685±20 A. The production of NCN A 3II is attributed to the formation of N2 A 3Σ NCN3→hv→NCN X3Σ+N 2 A 3Σ, with the threshold wavelength of 1915±30 Å followed by the sensitized reaction, N2 A 3Σ+NCN3→ NCN A 3II+2N2. Bond dissociation energies obtained from threshold energies are D(NC-N2) = 4.2±0.1 eV ( = 96±2 kcal mole-1) and D(NCN-N 2) = 0.3±0.1 eV ( = 7±2 kcal mole-1) where the error limit indicates an experimental uncertainty of the threshold energy measurements. Estimated heats of formation are ΔHf° (NCN3) = 4.7±0.2 eV ( = 108±5 kcal mole-1) and ΔHf°(NCN) = 5.0±0.2 eV ( = 115±5 kcal mole-1) from which D(N-CN) of 4.3±0.2 eV ( = 99±5 kcal mole-1) is obtained. The absorption coefficient of NCN3 in the region 1200 to 2000 Å has been measured. A comparison is made of bond energies of several azide compounds.