Association of molecular resonances with the oscillatory structures in nucleus–nucleus fusion cross section and its energy-weighted derivatives

Structures or peaks observed in the variation of measured results of nucleus–nucleus fusion cross section as a function of energy above the Coulomb barrier are believed to be associated with intermediate-structure and/or quasimolecular resonances of the ion–ion interaction. As a result of this oscillation in the fusion excitation function, the extracted values of the energy derivative of the excitation function times energy become oscillatory in the variation with incident energy showing several peaks and deeps including deeps of negative values. These structures are more pronounced in the fusion of light nuclei as compared to those in heavier ones. By a theoretical investigation we demonstrate how resonances give rise to oscillatory structures in the fusion cross sections and their energy-weighted derivatives and successfully reproduce the experimentally observed structures in the fusion data of the ¹⁶O+¹⁶O, ²⁸Si+²⁸Si, ¹⁶O+²⁰⁸Pb, ³⁶S+¹¹⁰Pd, ⁴⁰Ca+⁹⁶Zr, ⁴⁸Ca+⁹⁶Zr, and ⁵⁸Ni+⁶⁰Ni systems involving light as well as heavy nuclei. (paper)