Inverted Pairing and Excitation Induced by Quadrupole-Quadrupole Interaction

In this paper, eit is shown for a single-$j$ shell that the intrinsic excitations induced by the quadrupole-quadrupole interaction can be viewed as that due to the inverted surface-delta interaction whose multipole-pairing component with the largest spin is the dominant term and is attractive. This allow us to trace the origin of the recently introduced optimum pair description of rotation and leads naturally to analytical expressions for the rotational energies for the various bands in a single $j$-shell with the quadrupole-quadrupole interaction.