From molecular autoionization to thermionic emission

Abstract

Autoionization of Rydberg states and delayed ionization are two decay processes where the excess energy in the molecule or cluster is released by ejecting a free electron. While precise spectroscopic studies of molecular autoionization are commonly performed, allowing a very detailed understanding of the ongoing processes, the study of delayed ionization in clusters is by far less well known and its description is noticeably less precise. Indeed, in complex systems such as clusters, only a statistical approach is found to be suitable for describing the decay dynamics of the system. Beyond these apparent profound differences it is shown that both phenomena are actually two facets of the same general phenomenon and that delayed ionization, or thermionic emission in clusters, are analogous to molecular autoionization. The transition from autoionization of Rydberg states to delayed ionization, depicted as a transition from a process entirely described within the framework of quantum mechanics to a process described only in the framework of statistical mechanics may further be foreseen as a prototype of the transition from quantum to classical dynamics.

Keywords:

• Autoionization
• Rydberg states
• Thermionic emission
• Clusters

Acknowledgements

CB warmly acknowledges fruitful discussions with Christian Jungen in the early stages of this work. Contributions of Michel Broyer, Serge Martin, Pierre Labastie, Jacques Chevaleyre, Pierre-François Brevet, and Bernard Tribollet to the work on Na₂ Rydberg states are gratefully acknowledged. The work on clusters has also benefited from enlightening discussions with Klavs Hansen and Florent Calvo.