Fusion Doorway States in theC12+C12System

The role of isoscalar giant quadrupole excitations in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ as doorway states for symmetric fission and intermediate structure resonances in ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ elastic scattering is investigated by means of model calculations using particle-hole excitations over two major shells. The fission mode is treated as a shape degree of freedom that couples the giant quadrupole resonances in ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ to the ground state. The associated intermediate-structure resonances have calculated widths for symmetric fission and $\gamma$ decay that are in qualitative agreement with experiment.