A guided-ion beam study of the reactions of Xe+ and Xe2+ with NH3 at hyperthermal collision energies

We have measured the absolute cross sections for reactions of Xe+ and Xe2+ with NH3 at collision energies in the range from near-thermal to similar to 34 and similar to 69 eV, respectively. For Xe+, the cross section for charge transfer, the only exothermic channel, decreases from similar to 200 angstrom(2) below 0.1 eV to similar to 12 angstrom(2) at the highest energies studied. The production of NH3+ is the only channel observed below 5 eV, above which a small amount of NH2+ is also formed. In Xe2+ reactions, the main products observed are NH3+ and NH2+. The charge transfer cross section decreases monotonically from similar to 80 to similar to 6 angstrom(2) over the studied energy range. The NH2+ cross section is similar to the charge transfer cross section at the lowest energies, and exhibits a second component above 0.4 eV, with a maximum of 65 angstrom(2) at 0.7 eV, above which the cross section decreases to similar to 30 angstrom(2) at the highest energies studied. At energies above 10 eV, a small amount of NH+ is also observed in Xe2+ collisions. Product recoil velocity distributions were determined at selected collision energies, using guided-ion beam time-of-flight methods. (C) 2010 American Institute of Physics. [doi:10.1063/1.3488055]