Importance of nonlinear couplings in fusion-barrier distributions and mean angular momenta

The effects of higher-order coupling of surface vibrations to the relative motion on heavy-ion fusion reactions at near-barrier energies are investigated. The coupled-channels equations are solved to all orders, and also in the linear and the quadratic-coupling approximations. It is shown that the shape of fusion-barrier distributions and the energy dependence of the average angular momentum of the compound nucleus can significantly change when the higher-order couplings are included. The role of octupole vibrational excitation of ¹⁶O in the ¹⁶O + ¹⁴⁴Sm fusion reaction is also discussed using the all-order coupled-channels equations.