A molecular beam study of the H+N3 reaction. Product NH internal state distribution and electronic state branching ratio

The H+N3→NH(X 3∑−,a 1Δ, b 1∑+)+N2 reaction has been studied in a molecular beam-gas scattering arrangement in order to determine the nascent product state distribution. The NH product in specific rovibronic/fine-structure states has been detected by laser fluorescence excitation. The relative cross sections for formation of various vibrational levels in the a 1Δ electronic state were determined to equal 1:1.0±0.3:1.4±0.3:≤1.5 for v=0 through 3, inclusive, while the v=0 to v=1 population ratio in the X 3∑− state was found to be 1:0.015±0.003. The rotational distributions in all vibronic levels were found to be characterized by temperatures near 300 K, suggestive of relaxation of the nascent rotational distributions. By comparison of the populations of a specific pair of X 3∑− and a 1Δ state levels and with summation over the derived rovibrational distributions, an electronic state branching ratio of 3.2±1.3 was obtained for the X 3∑− to a 1Δ electronic state branching ratio. An upper limit of ≤0.02 was also derived for the ratio of the b 1∑+ v=0 to a 1Δ v=0 populations. These results are compared with NH fragment distributions observed in the photodissociation of HN3(X̃ 1A′) and with our expectations based on our fragmentary knowledge of HN3 potential energy surfaces.