The sub-Coulomb 12C + 12C resonances in a microscopic 12C+12C,[alpha]+20Ne, 8Be+16O cluster basis

Abstract

The low-J resonances in the Coulomb barrier region of the 12 C+12C system are investigated in the framework of a microscopic cluster model basis including 12C+12C, [alpha]+ 20Ne, and su8 Be+ 16O fragment decompositions. Calculations are carried out in an orthogonality condition model approximation in which Pauli-forbidden components are properly excluded from the basis but in which the interaction among cluster fragments is approximated by a local potential, obtained from a gaussian NN interaction by a folding procedure leading to both spherical and Q [middle dot] Q terms. Only minor adjustments of overall strength and fall-off parameters are introduced to gain a consistent picture of the low-energy spectrum in the separate rearrangement channels. The basis includes cluster relative motion excitations with oscillator quanta from 12 to 20 and is not quite rich enough to give a detailed quantitative comparison between theory and experiment. Predicted excitation energies are too high by ~ 3 MeV and predicted 12C partial widths are too small to indicate a well-developed surface-peaked molecular character; but it does appear possible to identify a 5 MeV region as the potential seat of the 0+, 2+, 4+ resonances. The number and approximate spacing of the resonance fine structure components are in agreement with experiment.