The soft Giant Monopole Resonance as a probe of the spin-orbit splitting

The isoscalar monopole response is studied in doubly magic ²⁰⁸Pb , ^{100, 132}Sn nuclei using the Skyrme HF+RPA model. A low-energy strength is predicted and corresponds to almost pure single-particle excitations. These pure single-particle excitations allow to analyse the splitting of the corresponding spin-orbit partners. A good agreement with the spin-orbit splitting data is found in the case of ²⁰⁸Pb . The experimental width of the giant monopole resonance may hinder the measurement of the soft monopole mode.