Conclusion the Rydberg signature and its implications

The alkali model and its extensions are fundamental to the development of atomic physics, and will be referred to several times in the course of the present monograph. 

In view of the fact that the Coulomb interaction between the electrons is long range, it may seem surprising that the atomic core should be of finite extent and, moreover, possess a fairly well-defined radius. This aspect is further discussed in chapter 5. 

While Rydberg series are usually prominent, on occasions they may also be absent, i.e. they may not be found at excitation energies at which they would have been expected. Such an observation can also be important, and may provide a valuable clue as to the nature of the excitation channel. 

The breakdown of exact one-electron quantisation may be more or less pronounced for a highly correlated system, i.e. one in which the electrons 

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