Guided-Ion Beam Study of the O+(4S) + NH3 System at Hyperthermal Energies

摘要

We have measured absolute cross sections for the reaction of ground- state 0+ with ammonia at collision energies in the range from near-thermal to approximately 15 eV, using the guided-ion beam (GIB) method. Measurements were also performed using ammonia-d3 to aid in mass assignments. The reaction is dominated at low collision energies by charge transfer; however, the cross section for this exothermic channel is rather small, decreasing sharply with energy from approx. 40 A2 for normal ammonia at near-thermal energies and leveling off at 3.7 A2 above 6 eV; the cross section is slightly smaller for ammonia-d3. Other channels, corresponding to the production of NH2+ and NO+ and possibly OH+, were detected. The NO+ channel, although nominally exothermic, is very small and exhibits a threshold of approx. 7 eV. Product recoil velocity distributions were also determined at selected collision energies, using GIB time-of-flight methods.