Vibrationally state-selected reactions of ammonia ions. I. NH+3(v)+D2

Abstract

Resonance enhanced multiphoton ionization has been applied to the production of vibrationally state‐selected ion beams. Ammonia ions are selectively formed with a specific number of vibrational quanta in the ν₂ umbrella bending mode. The effect of vibrational excitation of this mode on the reaction of NH⁺₃(X̃, v=0 to 9) with D₂ is examined over the 0.5 to 10 eV center‐of‐mass kinetic energy range in a tandem quadrupole mass spectrometer. Under these conditions, (1) abstraction of a D atom to form NH₃D⁺ is the dominant reaction channel, (2) NH₃D⁺ having sufficient internal energy may decompose to yield NH₂D⁺ and this decomposition process is enhanced by vibrational excitation of the NH⁺₃ reagent, and (3) NH₂D⁺ is also formed by direct hydrogen–deuterium exchange of NH⁺₃ with D₂, but this channel appears as a minor contribution which is insensitive to the vibrational excitation of the NH⁺₃. A spectator stripping model is able to account for the ratio of NH₂D⁺ to NH₃D⁺ as a function of the NH⁺₃ translational and vibrational energy.