Two-nucleon Excitation from p to sd Shell in 12,14C

The effect of the two-nucleon excitation from p to sd shell is discussed on 12C and 14C in the frame work of the nuclear shell model. The recently suggested shell-model Hamiltonian YSOX provides an suitable tool to investigate the 2 ~! excitation in psd region. Because the strength of the < pp|V |sdsd > interaction, which represents the interaction between the 0 and 2 ~! configurations, is considered in the construction of the Hamiltonian YSOX. The level of 12C is almost independent on the interaction, but excitation energies of certain states in 14C are strongly affected by it. Further investigation shows that the percentage of 2 ~! configuration in these states is quite different from that of the ground state. The non-linear effects of the < pp|V |sdsd > interaction on the configurations and transition rates are also discussed.