Classical trajectory multiple interaction simulations were used to study the bombardment of a clean, perfect, Cu target by low energy (<200 eV) O+ ions. Both attractive and repulsive Cu-O potential functions were investigated. At these energies, in this system, atom ejection is more sensitive to the shape of the ion-atom potential function than previously established for larger mass ratios. Significant atom size effects are recorded, but an attractive ion-atom potential function has no effect on atom ejection. The O+ bombardment led to unexpectedly high yields of Cu2 molecules. Below 100 eV, CuO molecules were formed which included the bombarding O+ ion. The internal (vibrational and rotational) energies of the ejected molecules are discussed. © 1986 Elsevier Science Publishers B. V. (North-Holland Physics Publishing Division).