Reactions of NH Radicals. I. Photolysis of HN3 Vapor at 313 nm

Photolysis of HN3 vapor was studied at 313 nm as a function of HN3 and Xe pressures, light intensity, and temperature. The photolysis of hydrazoic acid labeled with 15N was also studied. The quantum yields of N2, H2, and NH4N3 as a product were 4.85, 0.494, and 0.842 at 30 °C and 6.7 kPa of HN3, respectively. The mechanism for the main reactions was postulated as follows: HN3+hν(313 nm)→N2+NH(a1Δ); NH(a1Δ)+HN3→2N2+2H (2); NH(a1Δ)+HN3→N3+NH2 (3); NH(a1Δ)+HN3→N2+N2H2* (4). The rate constant ratios of k3⁄k2=0.746 and k4⁄k2=1.23 were obtained at 30°C. (k3+k4)⁄k2 decrease drastically with rising temperature. Xe is effective for the collisional deactivation, NH(a1Δ)+Xe→NH(X3Σ−)+Xe (15), and k15⁄(k2+k3+k4)=0.187 was obtained at 30 °C.