Intensities in the continuum

Continuity across the threshold is a fundamental property, which de- 

Since continuity across the threshold is so fundamental, it is worth testing the principle under conditions where / values can be measured to very high principal quantum numbers n, and where a strong intruding resonance located in the photoionisation continuum just above the threshold perturbs the course of intensities in the Rydberg series. An example of this kind occurs in the spectrum of Ba and is shown in fig. 4.3. The fact that, even in such a case, the df/dE curve joins completely smoothly shows that perturbations do not upset this principle, i.e. that it is of very general validity. 

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