Rydberg auto-ionization

Optical spectra of auto ionizing Rydberg states... 

Although in the case of pyrazine the interpretation is complicated by cross-term signals and auto-ionizing Rydberg states, the experimental and theoretical investigations nevertheless demonstrate the considerable potential of femtosecond time-resolved photoelectron spectroscopy. As a beautiful example of a more favorable case, Stolow and coworkers have recently presented time-resolved ionization studies on decatetraene. In direct analogy to the discussion presented above, they managed to monitor the S2 Si internal conversion associated with a conical intersection in real time. 

Fig.6.19a-d. Level schemes of ionization spectroscopy, (a) Photo-ionization, (b) excitation of auto-ionizing Rydberg levels, (c) two-photon ionization of excited molecules, (d) experimental arrangement for photoionization spectroscopy in a molecular beam... 

This auto-ionization process competes with the radiative decay of the Rydberg level, often also with possible predissociation. However, the spontaneous transition probability is approximately proportional to n 3. For large quantum numbers n the radiative decay therefore becomes very slow and even small auto-ionization probabilities may already result in complete auto-ionization of a Rydberg level if predissociation can be neglected. This means that the excitation of these molecular Rydberg levels above the ionization limit can be very effectively monitored through the resulting ion. 

We have therefore started in Kaiserslautern experimental investigations of auto-ionizing Rydberg states of Lig. The experimental procedure is illustrated in Fig. 8. The Lij molecules are prepared in a... 

Similar experiments on auto-ionization of molecular Rydberg levels have been performed on Naa and Kg by Martin et al.33 and by Leutwyler et al.34.35. / complete analysis of the auto-ionization spectra of all these alkali molecules is, however, still pending since a full understanding of all perturbations requires very detailed studies of the many molecular states closely below the ionization limit. These will not only be Rydberg states but also doubly excited states which can interact with the Rydberg states. For Lij such investigations are under way in our laboratory. 

S. Leutwyler, T. Heinis, and M. Jungen, Auto-ionizing Rydberg States in Nag, Chem. Phys. Lett. 87 (1982). 

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