Perturbation of Rydberg series by atomic compound states

The discrete spectrum of excited states of an atom contains Rydberg series of states and valence excited states, made up of electron orbitals with small principal quantum numbers. For an atom with a few electrons in the open outer shell the spectrum of the valence excited states is extremely dense and extremely complicated, and the corresponding atomic eigenstates are strongly chaotic and similar to nuclear compound states. This enables us to consider mixing of the Rydberg and compound valence atomic states in a general form as a function of the residual interaction strength. It appears that the mixing reaches its maximum for the 'physical' values of the interaction. The Rydberg series are strongly perturbed for n < D--1/3, where D is the mean level spacing between the compound states (in atomic units). For larger values of n the mixing is weak for any interaction strength. This follows from the separable character of the interaction between the Rydberg and compound states.