Excitation functions of the reactions ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{16}$O${,}^8$Be${)}^{20}$Ne and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{16}$O${,}^4$He${)}^{24}$Mg leading to several states have been measured in the range ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=25.7–38.6 MeV. From cross channel correlation analysis two intermediate resonance structures at ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=26.9 and 29.5 MeV corresponding to excitation energies of 43.7 and 46.2 MeV in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ have been identified. Angular distribution measurements for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$${(}^{16}$O${,}^4$He${)}^{24}$${\mathrm{Mg}}_{\mathrm{g}.\mathrm{s}.\mathrm{}}$ have also been made at the lower resonance at ${\mathit{E}}_{\mathrm{c}.\mathrm{m}.\mathrm{}}$=26.9 MeV which enable spin assignment of ${\mathit{J}}^{\mathrm{\pi }}$=${14}^{+}$ to this resonance. Striking observation of preferential ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$ decay of both the resonances to the 8-particle–4-hole states in ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ is interpreted as evidence for the resonances to be highly deformed shape isomeric configurations in ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ expected from deformed shell-model calculations.

• Received 23 December 1991

DOI:https://doi.org/10.1103/PhysRevC.47.1418