Atoms and molecules in highly excited (Rydberg) states have a number of unique characteristics due to the strong dependence of their properties on the values of principal quantum numbers. The paper discusses the results of an investigation of collisional Rydberg complexes specific features, resulting in the development of dynamic chaos and the accompanying diffusion autoionization processes. It is shown (experiment and theory) that, in subthermal low energies, the global chaotic regime that evolved in quasimolecular systems leads to significant changes in the Rydberg gases radiation/ionization kinetics. The effect of Förster resonance on the width of the fluorescence spectra and stochastic ionization processes in Rydberg systems is also discussed.
We have considered two types of interactions between particles resulting in autoionization of the intermediate Rydberg collisional complex. The first type is caused by the charge exchange processes inside the ionic core of the complex and is responsible for the formation of the final associative ionization channel due to the departure of a Rydberg electron (RE) of the complex to the energy continuum. We have investigated the evolution of the orbital momentum L of RE and discovered a non-trivial time dependence of L, demonstrating a contrasting oscillatory structure in both direction orientation and its absolute value. The second type of interaction, dipole-dipole interaction, dominates in cold highly excited gaseous media and leads to Penning ionization of various pairs of Rydberg atoms. We have found the optimal quantum configurations of atomic pairs, which intensify the PI rates by several orders of magnitude, and become important suppliers of charged particles upon the evolution of Rydberg gas into cold plasma.
Penning ionisation (PI) processes involving pairs of Rydberg alkali-metal atoms, excited to different quantum states and experiencing dipole–dipole interactions, have a wide range of important properties in atomic physics. Within the framework of the semiclassical approximation, we have used both numerical and analytical approaches to examine the Penning autoionisation width dependence on the state quantum numbers in a quasi-molecule formed by the interacting partner atoms. We described the characteristics of optimal quantum numbers that lead to enhanced PI widths for the interacting Rydberg atom pairs of all alkali-metal atoms. The excited states of atoms in these pairs are asymmetric, resulting in a large atomic shell size difference: inspired by Efimov et al (2016 J. Phys. B: At. Mol. Opt. Phys. 49 125302), we call such a pair ‘Tom’ and ‘Jerry’ (for ‘big’ and ‘small’). Compared to symmetric pairs, the optimal asymmetric pairs display a significant (by several orders of magnitude) increase in the PI rate. This property makes PI a relevant source for producing charged particles in cold Rydberg systems that spontaneously evolve into cold plasma. Contrary to hydrogen atoms examined in (Efimov et al 2016 J. Phys. B: At. Mol. Opt. Phys. 49 125302), the difference in quantum defects in alkali-metal atoms results in a strong Penning width dependence on the orbital quantum numbers l of the quasi-molecule. In particular, alkali-metal atoms exhibit two PI channels associated with bound–bound optical transitions showing Δl = ±1—individual and closely spaced (doublet-like) configurations of optimal pairs. Furthermore, we demonstrate that the presence of Förster resonances can lead to a notable (up to five times) increase in the PI efficiency.
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