Using two different guided ion beam machines the cross section for the slightly endothermic title reaction has been measured in a collision energy range which includes the threshold onset. High‐energy resolution has been achieved by combining a slow guided ion beam with a supersonic deuterium beam, in one case by crossing the two beams, in the other case by merging them. In a brief discussion the kinematic conditions are compared for the two geometries with those of a beam scattering cell arrangement. In contrast to previous low‐resolution measurements the present data clearly indicate a threshold, but, despite the high experimental resolution, it is not straightforward to extract a precise value of the reaction endothermicity or barrier since both reactants can contribute internal energy. Variation of the D2 rotational temperature proves that kinetic and rotational energy are equivalent in promoting the reaction. In contrast to that, the two beam experiments give some hints that energy from excited N+ fine structure states is inefficient. This is also corroborated by a low‐temperature ion trap study. With this assumption new phase space theory calculations have been performed to estimate threshold values. First evaluations indicate 11 meV for the reaction with H2 and 29 meV for the reaction with D2.

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