A guided-ion beam study of the reactions of Xe~+ and Xe ~(2+) with NH_3 at hyperthermal collision energies

摘要

We have measured the absolute cross sections for reactions of Xe+ and Xe2+ with NH_3 at collision energies in the range from near-thermal to ～34 and ～69 eV, respectively. For Xe+, the cross section for charge transfer, the only exothermic channel, decreases from ～200 ?~2 below 0.1 eV to ～12 ?~2 at the highest energies studied. The production of NH 3+ is the only channel observed below 5 eV, above which a small amount of NH 2+ is also formed. In Xe2+ reactions, the main products observed are NH 3+ and NH 2+. The charge transfer cross section decreases monotonically from ～80 to ～6 ?~2 over the studied energy range. The NH 2+ 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 ?~2 at 0.7 eV, above which the cross section decreases to ～30 ?~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.