Elastic Scattering of Oxygen Ions by Carbon, Magnesium, and Aluminum

Elastic scattering measurements have been carried out on the O+C, O+Mg, and O+Al systems using beams of ${\mathrm{O}}^{16}$ ions of precisely defined energy from the Chalk River tandem accelerator. Measurements have been made for energies near and above the Coulomb barrier appropriate to each system. Evidence for sharp ($\Gamma \sim 300$ keV) resonance structure is contained in a yield curve for O+C at a center-of-mass angle of 90°. This evidence is used to estimate $\frac{{\Gamma }_{\mathrm{elastic}}}{\Gamma }$ for the resonant states to be ∼7-10%. It is suggested that the resonant states involved may be similar to the "quasimolecular" states postulated to play an important role in the case of C+C scattering, although their appearance only at energies well above the Coulomb barrier, in contrast to the situation in C+C scattering, may allow a more conventional explanation. In the case of angular distributions for O+C, but not for O+Mg and O+Al, well-developed diffraction structure is observed. It is found that the simple sharp-cutoff models do not account quantitatively for the data although they do give the same qualitative features.