Sum rules and the disappearance of Rydberg series

One consequence of the appearance of a giant resonance in one excitation channel and the existence of sum rules for the oscillator strength (section 4.5) is the weakening or disappearance of oscillator strength for Rydberg series of the same channel. This can be explained in several different ways. 

Another description stresses the spatial overlap between the initial and final state wavefunctions the radius of the Ad initial state orbital is such as to have a large overlap with the inner well of the l = 3 double-well potential. Consequently, final state orbitals which are collapsed have a large spatial overlap with the initial state, giving rise to a large dipole matrix element and transition probability. On the other hand, final state orbitals which are eigenfunctions of the outer well (Rydberg orbitals) have very little spatial overlap with the Ad orbital, and give rise to very low transition probabilities. 

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