Angular momentum effects in subbarrier fusion ofMo64

Angular momentum distributions ${\sigma }_l$ for the compound nucleus ${}_{}{}^{164}{}_{}{}^{}\mathrm{Yb}$ were deduced from measurements of γ-ray multiplicity for all significant evaporation residues from fusion of ${}_{}{}^{64}{}_{}{}^{}\mathrm{Ni}$ and ${}_{}{}^{100}{}_{}{}^{}\mathrm{Mo}$. At the lowest bombarding energies the ${\sigma }_l$ extend to higher l values than do predictions of barrier-penetration models that include coupling of the principal inelastic channels, even if the coupling strengths are increased to match the experimental excitation function. Likewise, ${\sigma }_l$ from a real potential with an energy-dependent shape fitted to the excitation function fails to reproduce the experimental ${\sigma }_l$ distribution. Better success is achieved with models in which fusion occurs at large distances.