Molecular Beam Studies of the Dynamics of Reactions Involving the Azide Radical and Hydrazoic Acid

Several elementary reactions of atoms with N _3, HN_3, or halogens have been studied by laser fluorescence detection in a molecular beam-gas scattering arrangement approaching single -collision conditions. In the H + N_3, NCO to NH(X^3Sigma^ {-}, a^1Delta, b^1Sigma^{+}) + N_2, CO reactions, the NH product was detected. It was found in the N_3 reaction that product NH(a^1Delta ) carries considerable amount of vibrational energy (35% of the total available energy) while the NH(X ^3Sigma^{-}) product was vibrationally cold. An electronic state branching ratio of 3.2 +/- 1.3 was obtained for the X^3Sigma^{-} to a^1Delta electronic states. Comparison was made to the HN_3 (X ^1rm A^' ) photodissociation experiments and to our expectations based on our fragmentary knowledge of HN_3 potential energy surfaces. The corresponding NCO reaction was found to produce almost exclusively NH(X ^3Sigma^{-}) product due to the slight endothermicity of the NH(a^1 Delta) + CO channel. The total reaction cross section for H + NCO vs that for H + N_3 was estimated to be 1.2 +/- 0.3: 1. In the system of Ca, Sr + HN_3 , emission from electronically excited M( ^1P, ^3P), the MH(A ^2Pi, B^2Sigma ^{+}), and MOH(A^2 Pi, B^2Sigma^ {+}) was observed. The formation of MOH* was found due to a secondary reaction involving O _2 impurity in the HN_3 samples. Ground state MOH and MN_3 were detected but the search for CaNH was unsuccessful. All of the observed emissions can be explained as arising from secondary reactions of the metal imide (MNH) forced in the M + HN_3 primary reaction. A kinetic model shows that the M + HN_3 reaction proceeds mainly by formation of MNH, rather than MN_3. In the reactions of Pb + F_2 and Cl_2, the PbX products were detected. The PbCl product was observed in 18 vibrational levels of the ground electronic state with an average vibrational excitation of 21% of the total available energy. The PbF product was found to be characterized by a 300 K Boltzmann distribution for all the detected rovibrational states and proven to be an artifact. The radiative lifetimes of the PbF(A,B) and PbCl(A) states were also measured.