Charge-Exchange Cross Sections for Argon Ions in H2 and D2 below 1 keV

Charge-exchange cross sections for Ar+ ions incident on hydrogen and deuterium have been measured over the energy range of 30 to approximately 1000 eV. The argon-ion beam was formed by electron bombardment and electrostatic acceleration. Ionizing electron energy was nominally 18 eV, although the results appeared to be insensitive to this parameter. The measured cross sections for Ar++H2→Ar+H2+ as a function of ion energy are compared with the results of other investigators, which are in rather poor agreement. The measurements confirm that the cross section exhibits a maximum at approximately 180 eV incident-ion energy. Theoretical calculations by Gurnee and Magee and by Karmohapatro are discussed for this reaction. The cross section for Ar++D2→Ar+D2+ was also found to exhibit a maximum, but at approximately 85 eV, which is nearly the same center-of-mass energy as for the H2 target. The possible influence of ion—molecule reactions on the charge-transfer cross sections is discussed.