Isotopic differences in the fusion cross sections for 0+0, observed by Thomas, et al., are interpreted with a coupled-channel model. We find that most of the subbarrier enhancement of ${}_{}{}^{18}{}_{}{}^{}$O${+\mathrm{}}^{16}$O over ${}_{}{}^{16}{}_{}{}^{}$O${+\mathrm{}}^{16}$O is attributable to the excitation of the low $2^{+}$ state in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$. However, the model predicts the enhancement to persist above the barrier, contrary to experimental findings.

• Received 28 June 1985

DOI:https://doi.org/10.1103/PhysRevC.32.1432