Effect of the entrance channel mass asymmetry on the limitation of light heavy-ion fusion cross sections.

Evaporation residues resulting from the $^{11}\mathrm{B}$${+}^{27}$Al and $^{19}\mathrm{F}$${+}^{19}$F fusion reactions leading to the $^{38}\mathrm{Ar}$ compound nucleus and from the $^{19}\mathrm{F}$+${(}^{12}$C, $^{16}\mathrm{O}$, $^{27}\mathrm{Al}$, $^{40}\mathrm{Ca}$) reactions have been measured at incident energies 32 MeV\ensuremath{\le}${\mathit{E}}_{\mathit{L}}$${(}^{19}$F)\ensuremath{\le}72 MeV and 15 MeV\ensuremath{\le}${\mathit{E}}_{\mathit{L}}$${(}^{11}$B)\ensuremath{\le}50 MeV. The hindrance of the fusion cross sections, at energies above the interaction barrier, show a clear dependence on the entrance channel mass asymmetry. This dependence is discussed in terms of model predictions that treat explicitly the mass asymmetry degree of freedom.