Reduced dimensionality wave packet study of the NH3++H2, D2 reaction

The reaction between NH3+ and D2 (or H2), leading to NH3D++D (or NH4++H) is investigated using a quantum wave packet approach at a collision energy below 2.5 eV. The study is restricted to the collinear geometry preserving C3v symmetry. Three degrees of freedom are explicitly treated: the reactive D–D and N–D distances, and the umbrella angle of NH3. The effects of the initial vibrational excitation of D2 (or H2) and of the umbrella motion of NH3+ are studied. The reaction probability is found to be large and to decrease with internal excitation of the reagents. The state-to-state reaction probabilities for the two isotopic variants differ qualitatively. This is related to the existence of a Fermi resonance in the geometrically constrained NH4+ ion, which does not exist in NH3D+. The umbrella motion is found to play an active role in the reactivity at a collision energy above 1 eV.