The influence of $\alpha$ clustering on nuclear reaction dynamics is investigated using the giant dipole resonance (GDR) lineshape studies in the reactions ${}^{20}\mathrm{Ne}$ ($E_{\mathrm{lab}}=145,160$ MeV) $+$ ${}^{12}\mathrm{C}$ and ${}^{20}\mathrm{Ne}$ ($E_{\mathrm{lab}}=160$ MeV) $+$ ${}^{27}\mathrm{Al}$, populating ${}^{32}\mathrm{S}$ and ${}^{47}\mathrm{V}$, respectively. The GDR lineshapes from the two systems are remarkably different from each other. Whereas, the non-$\alpha$-like ${}^{47}\mathrm{V}$ undergoes Jacobi shape transition and matches exceptionally well with the theoretical GDR lineshape estimated under the framework rotating liquid drop model (RLDM) and thermal shape fluctuation model (TSFM) signifying shape equilibration, for the $\alpha$ cluster ${}^{32}\mathrm{S}$ an extended prolate kind of shape is observed. This unusual deformation, seen directly via $\gamma$ decay for the first time, is predicted to be due to the formation of orbiting dinuclear configuration or molecular structure of ${}^{16}\mathrm{O}$ $+$ ${}^{16}\mathrm{O}$ in the ${}^{32}\mathrm{S}$ superdeformed band.

• Received 17 February 2010

DOI:https://doi.org/10.1103/PhysRevC.81.061302