Rydberg states, double photoionization

The prototypical indirect double photoionization process is the classical Auger effect, where the single-hole state created by ejection of an inner-shell electron exists for a significant time before ejection of a second electron. Alternatively, an intermediate singly charged state may exist as a multiply excited valence state or a Rydberg state, but whatever its nature, a lifetime of at least a few femtoseconds will normally allow the whole process to be considered as a sequence of two distinct steps. A sharp peak in the photoelectron spectrum and also, therefore, in... 

R. Zhao, l.M. Konen, R.N. Zare, Optical-optical double resonance photoionization spectroscopy of nf Rydberg states of nitric oxide. J. Chem. Phys. 121, 9938 (2004)... 

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