Experimental Observation of Interatomic Coulombic Decay in Neon Dimers

Abstract

Recently Cederbaum et al. [Phys. Rev. Lett. 79, 4778 (1997)]] predicted a new decay channel of excited atoms and molecules termed interatomic Coulombic decay (ICD). In ICD the deexcitation energy is transferred via virtual photon exchange to a neighboring atom, which releases it by electron emission. We report on an experimental observation of ICD in 2s ionized neon dimers. The process is unambiguously identified by detecting the energy of two Ne1+ fragments and the ICD electron in coincidence, yielding a clean, background free experimental spectral distribution of the ICD electrons.

Experimental Separation of Virtual Photon Exchange and Electron Transfer in Interatomic Coulombic Decay of Neon Dimers

“…Figure 2(a) shows that distribution on a logarithmic color scale. Apart from the structures described in [3], a set of new features appears at higher KERs and photo electron energies that do not belong to ICD or 2s photoionization. In order to identify the origin of those features, Fig.…”

“…Our expectation is the following. Shakeup states of even parity -just like the 2s ionized state investigated so far [2,3]-can decay to the 2p ionized ground state via virtual dipole photon emission (i.e., the dipole-allowed virtual photon exchange ICD channel is open), whereas decay from excited states of odd parity to the ionized ground state is dipole forbidden, and thus the ICD takes place only at small R where the overlap of the orbitals becomes significant. Measuring R at the instance of ICD by detecting the kinetic energy release (KER) for each shakeup state separately, we have successfully demonstrated that the dipole-allowed ICD takes place at the instant of photoionization at the equilibrium R of the ground state, whereas the dipole-forbidden ICD takes place only after shortening of R, i.e., contraction of the dimer.…”

“…As ICD occurs, the energy of an excited atom in van der Waals or hydrogen bound matter is used to release a low energy electron from a neighboring atom. During the last three years, the existence of ICD has been proven experimentally by means of electron spectroscopy [2] and multiparticle coincidence momentum spectroscopy techniques (COLTRIMS) [3]. Later experimental evidence of ICD in species other than a neon cluster was found, as well [4].…”

“…In [3], the key figure [ Fig. 4(a)] showed the measured electron energy in dependence of the KER of the Coulomb exploding dimer.…”

On the nature and origin of dicationic, charge-separated species formed in liquid water on X-ray irradiation

“…[10][11] In recent years a set of novel non-local autoionization processes has been identified to play an important role in weakly bonded atomic and molecular systems. [12][13][14] One such relaxation process is Intermolecular Coulombic Decay (ICD), initially observed upon innervalence ionization of van der Waals-bonded clusters, 12,[15][16][17] and later also (hydrogen bonded) water clusters. 18 In the ICD process, the energy provided by an outer valence electron upon filling the vacancy is used to expel a second electron from an atom or molecule neighboring the initially ionized site.…”