Shell model description of the decay out of the superdeformed band of 36Ar.

Large scale shell model calculations in the valence space spanned by two major oscillator shells (sd and pf) describe simultaneously the superdeformed excited band of 36Ar and its spherical ground state. We explain the appearance of this superdeformed band at low excitation energy as a consequence of the very large quadrupole correlation energy of the configurations with many particles and many holes (np-nh) relative to the normal filling of the spherical mean field orbits (0p-0h). We study the mechanism of mixing between the different configurations to understand why the superdeformed band survives and how it finally decays into the low-lying spherical states via the indirect mixing of the 0p-0h and 4p-4h configurations.