Collisional Excitation ofAr*+O2Mediated by Ion-Pair Formation

For ${\mathrm{Ar}}^{*}$ + ${\mathrm{O}}_2$ collisions at ≈ 100 eV energies an intense rainbow peak has been observed in the neutral-product angular distribution. The surprisingly large inelasticities (1-2 eV) and the absence of elastic scattering in this small-angle feature are explained by a charge-transfer model involving transient formation of an ${\mathrm{Ar}}^{+}$ + ${\mathrm{O}}_2^{-}$ intermediate. Large product inelasticities are understood by examing the relative timing of the projectile motion and the ${\mathrm{O}}_2^{-}$ vibration on the intermediate surface.