Site- and energy-selective slow-electron production through intermolecular Coulombic decay

Citation metadata

From: Nature(Vol. 505, Issue 7485)
Publisher: Nature Publishing Group
Document Type: Report
Length: 5,488 words
Lexile Measure: 1520L

Document controls

Main content

Article Preview :

Irradiation of matter with light tends to electronically excite atoms and molecules, with subsequent relaxation processes determining where the photon energy is ultimately deposited and electrons and ions produced. In weakly bound systems, intermolecular Coulombic decay (1) (ICD) enables very efficient relaxation of electronic excitation through transfer of the excess energy to neighbouring atoms or molecules that then lose an electron and become ionized (2-9). Here we propose that the emission site and energy of the electrons released during this process can be controlled by coupling the ICD to a resonant core excitation. We illustrate this concept with ab initio many-body calculations on the argon-krypton model system, where resonant photoabsorption produces an initial or 'parent' excitation of the argon atom, which then triggers a resonant-Auger-ICD cascade that ends with the emission of a slow electron from the krypton atom. Our calculations show that the energy of the emitted electrons depends sensitively on the initial excited state of the argon atom. The incident energy can thus be adjusted both to produce the initial excitation in a chosen atom and to realize an excitation that will result in the emission of ICD electrons with desired energies. These properties of the decay cascade might have consequences for fundamental and applied radiation biology and could be of interest in the development of new spectroscopic techniques.

Since its prediction (1) in 1997, ICD has been successfully investigated in a variety of systems (7). It usually proceeds on a femtosecond timescale and becomes faster the more neighbours are present, often dominating most of the competing relaxation processes. ICD remains effective over considerable interatomic distances: in He dimers, the weakest bound systems known in nature, it is operative over distances of about 45 times the atomic radius (8, 9). The initial electronic excitation triggering ICD may be produced directly by photoabsorption, electron impact or even ion impact, as demonstrated recently (10). It can also result from multistage processes such as Auger decay (11-13), with the overall Auger-ICD cascade initiated by core ionization of an atom (typically through X-ray absorption) that is part of a more complex system. In this case, however, there is little control over where exactly the Auger decay is triggered and where the subsequent ICD takes place. Indeed, in a polyatomic system, all atoms with core-ionization potentials below the energy of the impacting photon may become ionized and undergo an Auger transition.

Our proposal for realizing ICD with control over both the location of the process and the energies of the emitted ICD electrons exploits resonant Auger decay (14). It uses photons with an energy just below the core-ionization threshold of a selected atom in a larger system, so that at a number of discrete energies the core electron will resonantly absorb the photon and be promoted to some bound, unoccupied orbital to give a highly energetic, core-excited state that can decay through the emission of an Auger electron. In this process, a valence electron fills the initial vacancy and another valence electron is...

Source Citation

Source Citation   

Gale Document Number: GALE|A361351610