Ultralong-range energy transfer by interatomic Coulombic decay in an extreme quantum system

Abstract

Interatomic Coulombic decay is a recently discovered ionization process by which energy absorbed from incident radiation by one atom is rapidly transferred to another. A study of this process in helium now shows that it can operate over remarkably long distances of more than 45 atomic radii. When an atom is electronically excited, it relaxes by emitting a photon or an electron. These carry essential information on the electronic structure of their emitter. However, if an atom is embedded in a chemical environment, another ultrafast non-radiative decay process called interatomic Coulombic decay (ICD) can become operative1. As ICD occurs only in the presence of neighbours, it is highly sensitive to that environment. Therefore, it has the potential to become a powerful spectroscopic method to probe the close environment of a system. ICD has been observed experimentally in van der Waals clusters2,3,4,5 as well as in hydrogen-bonded systems6,7,8. A key feature of ICD is that the excited atom can transfer its excess energy to its neighbours over large distances. The giant extremely weakly bound helium dimer is a perfect candidate to investigate how far two atoms can exchange energy. We report here that the two helium atoms within the dimer can exchange energy by ICD over distances of more than 45 times their atomic radius. Moreover, we demonstrate that ICD spectroscopy can be used for imaging vibrational wavefunctions of the ionized–excited helium dimer.