The isospin splitting of isovector monopole excitations

The excitation energy of the isovector monopole state is calculated for a series of nuclei with N > Z using a simple residual particle-hole interaction and a basis of wave functions which conserve isospin. Such wave functions include 2p2h configurations in addition to 1p1h states. The splitting between the T0 + 1 and T0 components of the isovector monopole state is obtained. Using the wave function of the T0 + 1 component the amount of isospin mixing in the ground states is estimated. (orig.)