Quasiclassical Trajectory Study of NH(3Σ–) + NH(3Σ–) Reactive Collisions: The Role of Vibrational Energy

Abstract

We present a quasiclassical trajectory study of the reaction NH(3Σ–) + NH(3Σ–) → N2 + H + H to investigate the role of vibrational excitation of the reactants. Using the global six-dimensional DMBE potential energy surface for the singlet ground state of N2H2 (Poveda, L. A.; etal. J. Chem. Phys., 2009, 131, 044309). we characterize the singlet-surface contribution to this reaction. We ran trajectories for NH(v, 1) colliding with NH(v′, 1), with v = 1–5, covering both the case where a single reactant carries vibrational excitation (v′ = 0) and the case where both do (v = v′), for translational energies 0.1 ≤ Etr/kcal mol–1 ≤ 10. As in our previous study, the dominant product channel is N2 + H + H, formed via competing one-step and two-step (N2H-intermediate) microscopic mechanisms. At low translational energy, states in which both reactants are vibrationally excited show a larger two-step contribution than the corresponding singly excited states. A comparison of three states with nearly matched total vibrational energy, (4, 0), (3, 1), and (2, 2), shows that the distribution of vibrational energy between the reactants affects the mechanism branching: above a few kcal mol–1, sharing the excitation between both reactants favors the one-step mechanism, whereas the enhanced two-step contribution at the lowest collision energies is specific to (2, 2). The vibrational energy content of the nascent N2 increases markedly with reactant vibrational excitation. Reactive cross sections, excitation functions, and rate constants are also reported.