A new phenomenological model for heavy-ion fusion cross sections.

We describe a novel universal phenomenological formula that is able to reproduce, with a few parameters, experimental data of fusion excitation functions obtained in heavy-ion collisions, in a broad domain of masses and asymmetries and with unprecedented accuracy. Within the approach adopted in this paper, we observe the occurrence of a saturation behaviour for the critical angular momentum as a function of the compound excitation energy; for medium-light systems, the extracted limiting angular momenta are in reasonable agreement both with experimental values and theoretical predictions based on the liquid drop model. A detailed comparison of our predictions with experimental data suggests the occurrence of possible nuclear structure effects in the fusion of systems with nearly zero fusion $Q$-values.