We have studied the scattering of low energy O- and O+ ions off a clean Cu(
001) surface in order to gain further insight into nonadiabatic electron tr
ansfer processes during reactive ion-surface collisions. For incident energ
ies of 0.45 keV, we have measured O+/O- ratios and the absolute yields of p
ositive, negative, and neutral oxygen atoms in the scattered flux over a wi
de range of scattering geometries. We have determined the extent to which m
emory loss occurs by comparing O+/O- ratios for single scattering events, o
btained with incident O- ions and identified with a classical trajectory si
mulation, to those made in a similar study [C.A. Keller, A.C. Lavery, B.H.
Cooper, Phys. Rev. B. 58 (1998) 10959] that was performed using incident O ions; The neutral and negative ions observed in the scattered flux can be
explained with a simple model based on the energetics of resonant charge ex
change. The presence of scattered positive ions, however, is explained by i
nvoking a collisional mechanism for their production. (C) 1999 Elsevier Sci
ence B.V. All rights reserved.