Topical Review - Atomic Physics
Review of experimental and theoretical research on positronium ions and molecules
Department of Physics, Faculty of Sciences, Science and Research Branch, Islamic Azad University, Tehran, Iran
2 Department of Physics and Astronomy, York University, M3J 1P3, Toronto, ON, Canada
Accepted: 21 May 2021
Published online: 28 June 2021
In this review we discuss the status of the research for the three-body positronium negative ion (, ) and the four-body positronium molecule (, ) from both theoretical and experimental points of view. Experimental results are included to compare with theoretical predictions. J. A. Wheeler, during the 1940s, proved that has a stable bound state and he also speculated that larger systems such as can exist. There have been several theoretical works starting from the 1940s about the properties of and . However, experimental observation of such exotic systems proved to be challenging. Thus, was first observed in 1981 and Ps was only seen in 2007. During recent decades, there have been major advances in determining the properties of the positronium negative ion and the positronium molecule. These studies shed light on the properties of such exotic systems and allow us to better understand and test the theory of quantum electrodynamics (QED).
© The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature 2021