Spins and Partial Widths of Quasimolecular Resonances inC12+C12Interactions

Angular distributions for the reaction ${\mathrm{C}}^{12}({\mathrm{C}}^{12}, \alpha ){\mathrm{Ne}}^{20}$ to levels in ${\mathrm{Ne}}^{20}$ at 0, 1.63, 4.25, and 4.97 MeV and an unresolved doublet at 5.63-5.80 MeV have been studied at incident energies near 6 MeV in the center-of-mass system. The results strongly suggest spins 2 and 4 for the "quasimolecular" states at 19.5- and 19.9-MeV excitation in ${\mathrm{Mg}}^{24}$. The partial widths of these states reduced to units of $\frac{{\hslash }^2}{M{R}^2}$ appropriate to each channel are given; in these units the ${\mathrm{C}}^{12}$ width is more than ten times the average width for $\alpha$-particle emission and one hundred times the average nucleon width. The nature of these states, which are prominent in the total reaction cross section, is discussed.