Ionic Collision Processes in Gaseous Ammonia

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Abstract
Rate coefficients for reactions resulting from collisions of NH3+ and NH2+ with NH3 have been measured as a function of primary ion translational energy over the energy range 0–8.0 eV. NH4+ was the only observed product of NH3+/NH3 collisions. The rate coefficient drops sharply with increasing energy from 18.1 × 10−10 cm3 molecule−1·sec−1 for thermal ions to 10.2 × 10−10 cm3 molecule−1·sec−1 for ions with a maximum translational energy (KE) of 1 eV. Above 3 eV an essentially constant value of 8 × 10−10 cm3 molecule−1·sec−1 is obtained. Collisions of NH2+/NH3 result in the production of both NH4+ and NH3+. With increasing ion energy below 1 eV the relative number of collisions which proceed via the less exoergic mechanism increases. Above 3‐eV KE the rate coefficient for the removal of NH2+ increases which is taken to indicate that in this energy range the cross section for electron transfer is greater than that for ion–molecule reaction. The rate coefficient for NH4+ production drops to an undetectable level at about 2‐eV KE rising again above 3‐eV KE. It is proposed that this new onset can be attributed to the endoergic reaction in which the neutral products are N+H and not NH as is supposed for the proton‐transfer process at lower ion energies.

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