Interatomic Coulombic Decay Process Research Articles

Interference effects in the photoelectron spectrum of the NeKr dimer and vibrationally selected interatomic Coulombic decay

In our work we study the interatomic Coulombic decay (ICD) in the NeKr dimer, where after $2s$ ionization of the Ne, the system relaxes and the excess energy is utilized to ionize the Kr. The temporal evolution of the ICD process in NeKr has been recently measured and theoretically explained by Trinter et al. [Chem. Sci. 13, 1789 (2022)]. Here we focus on two other main goals. The first goal regards the found interference effects in the photoemission (PE) spectrum, which are unusual phenomena in noble gas dimers. They result from the coherently excited vibrational energy levels and substantial dependence of the large ICD decay width on the internuclear distance. The PE spectrum reacts sensitively to changes in the potential energy curve (PEC) of the $2s$ ionized state, and we modified the available ab initio PEC in such a way that satisfactory agreement between theoretical and experimental data is achieved. The impact of isotope masses on the PE spectrum is briefly discussed and used in the determination of the PEC. Our second main goal concerns the nuclear motion during the ICD process. Here we investigate the impact of different vibrationally excited states of the electronic ground state on the ICD-electron and kinetic energy release (KER) spectra. To transfer our vibrationally selected ICD model to a realizable experiment, we also present the impact of temperature on the ICD-electron spectrum. Finally, our studies are complemented by comparing the directly computed KER spectrum to the mirror image of the ICD-electron spectrum, which coincide under certain conditions.

Impact of intense ultrashort laser on Interatomic Coulombic decay in the NeAr dimer

The exposure of Ne-Ar dimer to an intense ultrashort laser can trigger a variety of competing ionization processes in addition to the already predicted interatomic Coulombic decay (ICD). The question of how and to what extent these competing ionization processes influence the line shape of the electron spectrum obtained for an ICD is addressed to in this work. The calculations predict that ionization from the ICD and final ionic states significantly influences the line shape of the electron spectrum. The time resolved electron spectrum for an only ICD process was calculated by employing an analytical expression. A line splitting in the ICD spectrum is observed at a comparatively higher peak intensity and systematic analysis involving time resolved electron spectrum indicates that the splitting is caused due to the effect of photoionization from the final ionic state. The effects of the ponderomotive shift of the free electron released prior to the ICD step on the ICD electron spectra were also estimated.

Extreme Ultraviolet Wave Packet Interferometry of the Autoionizing HeNe Dimer.

Femtosecond extreme ultraviolet wave packet interferometry (XUV-WPI) was applied to study resonant interatomic Coulombic decay (ICD) in the HeNe dimer. The high demands on phase stability and sensitivity for vibronic XUV-WPI of molecular-beam targets are met using an XUV phase-cycling scheme. The detected quantum interferences exhibit vibronic dephasing and rephasing signatures along with an ultrafast decoherence assigned to the ICD process. A Fourier analysis reveals the molecular absorption spectrum with high resolution. The demonstrated experiment shows a promising route for the real-time analysis of ultrafast ICD processes with both high temporal and high spectral resolution.

Interatomic Coulombic decay of a Li dimer in a coupled electron and nuclear dynamics approach

Interatomic Coulombic decay (ICD) is a fundamental process between atoms or molecules via a neighbor interaction that produces a relaxation of an electronically excited atom or molecule when embedded in an environment. Due to the physical nature of the process, the electronic and nuclear degrees of freedom are coupled. In this paper, we study the ICD process for a lithium dimer by means of the electron and nuclear dynamics (END) approach. The END approach incorporates a full time-dependent description of the electronic and nuclear degrees of freedom, although its current version does not properly account for continuum states and has limitations in the electronic description by using a single determinantal wave function. Despite this, we confirm that the ICD process takes place via a dipole interaction that induces the nuclear motion of the dimer with a consequent electronic population transfer to higher excited states simulating the ionization process. When the dimer approaches a distance of around 11.5 a.u. (6 \AA{}), this ionization process takes place due to the dipole coupling and occurs at the place of the strongest attractive dipole force. Passing that point, we find that the two lithium atoms repel each other via a Coulomb explosion process followed with a consequent kinetic-energy release (KER). We determine the KER and the timing of the ICD process. We point out the strengths and weaknesses of the END approach and the required enhancements to account for a better description of the ICD process in a coupled electron and nuclear dynamics.

Mechanism of superexchange interatomic Coulombic decay in rare-gas clusters

Interatomic Coulombic decay (ICD) is an ultrafast energy transfer process. Via ICD, an excited atom can transfer its excess energy to a neighboring atom which is thus ionized. On the example of the NeHeNe cluster, we recently reported [Phys. Rev. Lett. 119, 083403 (2017)] that the total ICD widths are substantially enhanced in the presence of an ICD inactive atom. The enhancement occurs due to the coupling of the resonance state to intermediate virtual states of the bridge atom---a mechanism named superexchange ICD. In this followup work, we analyze the partial ICD widths in the NeHeNe cluster and show that only some channels are affected by the superexchange ICD process. Furthermore, we consider superexchange ICD in NeHeAr. We show that in this system the enhancement is still present but the energy transfer mediated by the superexchange mechanism is less efficient than in NeHeNe owing to the different ionization potentials of Ar and Ne. The behavior of the computed ICD widths is explained with a simple model based on first-order perturbation theory and a Hartree-Fock-like description of the states.

Virtual Photon Approximation for Three-Body Interatomic Coulombic Decay.

Interatomic Coulombic decay (ICD) is a mechanism that allows microscopic objects to rapidly exchange energy. When the two objects are distant, the energy transfer between the donor and acceptor species takes place via the exchange of a virtual photon. On the contrary, recent abinitio calculations have revealed that the presence of a third passive species can significantly enhance the ICD rate at short distances due to the effects of electronic wave function overlap and charge transfer states [Phys. Rev. Lett. 119, 083403 (2017)PRLTAO0031-900710.1103/PhysRevLett.119.083403]. Here, we develop a virtual photon description of three-body ICD, allowing us to investigate retardation and geometrical effects which are out of reach for current abinitio techniques. We show that a passive atom can have a significant influence on the rate of the ICD process at fairly large interatomic distances, due to the scattering of virtual photons off the mediator. Moreover, we demonstrate that in the retarded regime ICD can be substantially enhanced or suppressed depending on the position of the ICD-inactive object, even if the latter is far from both donor and acceptor species.

The influence of retardation and dielectric environments on interatomic Coulombic decay

Interatomic Coulombic decay (ICD) is a very efficient process by which high-energy radiation is redistributed between molecular systems, often producing a slow electron, which can be damaging to biological tissue. During ICD, an initially-ionised and highly-excited donor species undergoes a transition where an outer-valence electron moves to a lower-lying vacancy, transmitting a photon with sufficient energy to ionise an acceptor species placed close by. Traditionally the ICD process has been described via ab initio quantum chemistry based on electrostatics in free space, which cannot include the effects of retardation stemming from the finite speed of light, nor the influence of a dispersive, absorbing, discontinuous environment. Here we develop a theoretical description of ICD based on macroscopic quantum electrodynamics in dielectrics, which fully incorporates all these effects, enabling the established power and broad applicability of macroscopic quantum electrodynamics to be unleashed across the fast-developing field of ICD.

Interatomic relaxation processes induced in neon dimers by electron-impact ionization

We report an experimental observation of the interatomic Coulombic decay (ICD) and radiative charge-transfer (RCT) processes in a Ne dimer $(e,2e)$ following a 380-eV electron impact. By detecting the $\mathrm{N}{\mathrm{e}}^{+}\ensuremath{-}\mathrm{N}{\mathrm{e}}^{+}$ cation pair and one of the emitted electrons in coincidence, the fingerprint of the ICD process initiated by the inner-valence ionization of Ne is obtained. Furthermore, the experimental results and ab initio calculations together unambiguously confirm the occurrence of the RCT process, and we show that most of the low-energy electrons produced in ionization of the Ne dimers are due to the ICD, which strongly suggests the importance of the ICD in causing radiation damage in a biological medium.

Observation of fast and slow interatomic Coulombic decay in argon dimers induced by electron-impact ionization

We investigate the interatomic Coulombic decay (ICD) in argon dimers induced by electron-impact ionization (${E}_{0}=90\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$) using a multiparticle coincidence experiment in which the momentum vectors and, consequently, the kinetic energies for electrons and fragment ions are determined. The signature of the ICD process is obtained from a correlation map between ejected electron energy and kinetic energy release (KER) for ${\mathrm{Ar}}^{+}+{\mathrm{Ar}}^{+}$ fragment ions where low-energy ICD electrons can be identified. Furthermore, two types of ICD processes, termed fast and slow interatomic decay, are separated by the ICD initial-state energies and projectile energy losses. The dependence of the energies of emitted low-energy ICD electrons on the initial-state energy is studied. ICD electron energy spectra and KER spectra are obtained separately for fast and slow decay processes where the KER spectra for the slow decay channel are strongly influenced by nuclear motion. The KER and ICD electron energy spectra are well reproduced by ab initio calculations.

Strong field control of the interatomic Coulombic decay process in quantum dots

In recent years the laser-induced interatomic Coulombic decay (ICD) process in paired quantum dots has been predicted (Bande, 2013). In this work we target the enhancement of ICD by scanning over a range of strong-field laser intensities. The GaAs quantum dots are modeled by a one-dimensional double-well potential in which simulations are done with the space-resolved multi-configuration time-dependent Hartree method including antisymmetrization to account for the fermions. As a novelty a complementary state-resolved ansatz is developed to consolidate the interpretation of transient state populations, widths obtained for the ICD and the competing direct ionization channel, and Fano peak profiles in the photoelectron spectra. The major results are that multi-photon processes are unimportant even for the strongest fields. Further, below-π to π pulses display the highest ICD efficiency while the direct ionization becomes less dominant.

Interatomic Coulombic decay and electron-transfer-mediated decay following triple ionization of Ne2 and NeAr

We report observations of the interatomic Coulombic decay (ICD) and electron-transfer-mediated decay (ETMD) from the triply charged states in Ne2 and NeAr dimers. The ICD processes leading to fragmentation of Ne3+-Ne into Ne3+-Ne+ and Ne3+-Ar into Ne3+-Ar+, and ETMD processes leading to fragmentation of Ne3+-Ne into Ne2+-Ne2+ are unambiguously identified by electron–ion-ion coincidence spectroscopy in which the kinetic energy of the ICD or ETMD electron and the kinetic energy release between the two fragment ions are measured in coincidence.

Geometrical control of the interatomic coulombic decay process in quantum dots for infrared photodetectors.

In electron dynamics calculations the interatomic Coulombic decay (ICD) process has recently been shown to take place in two vertically-aligned quantum dots (QDs). Energy emitted during the relaxation of one electron in one QD is converted into kinetic energy of another electron ejected from a neighboring QD. As the electronic structure of QDs can be controlled by their geometries, we prove here in thorough scans of the transversal and vertical QD confinement potentials' widths that geometries are likewise control parameters for ICD. Such a comprehensive investigation has been enabled by a significant development of the calculations in terms of speed achieved among others by optimization of the grid and Coulomb interaction operator representations. As key result of this study we propose two cigar-shaped singly-charged GaAs QDs vertically aligned in the direction of their long side for a most efficient QD ICD realization useful for an infrared photodetector. © 2016 Wiley Periodicals, Inc.

Interatomic Coulombic Decay in Low Energy Ion-Dimer Collisions

SynopsisLow energy collisions between ions and neon dimers are investigated, focusing attention on the dissociation of the ionized molecular target. The results show a clear dependance of the processes with the projectile charge state and an unexpected appearance of inner-shell single electron capture from one site of the neon dimer leading to interatomic coulombic decay process and low energy electrons emission.

Interatomic Coulombic decay in two coupled quantum wells

Interatomic coulombic decay (ICD) is a relaxation process induced by electronic correlation. In this work we study the ICD process in a two coupled Quantum wells (QWs) nano-structure. We study a simple one-dimensional effective potential using experimental parameters of the semiconductor QW layers i.e. using the single band effective-mass approximation . In our calculations we consider the discontinuity of the effective mass of the electron in each of the QW layers. We control the ICD lifetime by changing the distance between the two wells. The expected overall trend is a decrease of ICD lifetime with a decrease in the distance between the wells. We show that the distance can be tuned such that the emitted ICD electron is trapped in a meta-stable state in the continuum i.e. a one electron resonance state. This causes the life time of the ICD to be an order of magnitude smaller even in very long distances, and improves the efficiency of the ICD. For the ICD to be dominant decay mechanism it must prevail over all other possible competitive decay processes. We have found that the lifetime of the ICD is on the timescale of picoseconds. Therefore, based on our results we can design an experiment that will observe the ICD phenomenon in QWs nano-structure for the first time. This work can lead to designing a wavelength sensitive detector which is efficient even in low intensities.

Interatomic Coulombic decay as a new source of low energy electrons in slow ion-dimer collisions.

We provide the experimental evidence that the single electron capture process in slow collisions between O^{3+} ions and neon dimer targets leads to an unexpected production of low-energy electrons. This production results from the interatomic Coulombic decay process, subsequent to inner-shell single electron capture from one site of the neon dimer. Although pure one-electron capture from the inner shell is expected to be negligible in the low collision energy regime investigated here, the electron production due to this process overtakes by 1 order of magnitude the emission of Auger electrons by the scattered projectiles after double-electron capture. This feature is specific to low charge states of the projectile: similar studies with Xe^{20+} and Ar^{9+} projectiles show no evidence of inner-shell single-electron capture. The dependence of the process on the projectile charge state is interpreted using simple calculations based on the classical over the barrier model.

The effect of the partner atom on the spectra of interatomic Coulombic decay triggered by resonant Auger processes.

The resonant-Auger - interatomic Coulombic decay (ICD) cascade was recently suggested as an efficient means of controlling the course of the ICD process. Recent theoretical and experimental works show that control over the energies of the emitted ICD electrons can be achieved either by varying the photon energy to produce different initial core excitations or by changing the neighboring species. This work presents a theoretical investigation on the role of the rare-gas neighbor and clarifies how the latter influences the ICD process. For this purpose, we compare fully ab initio computed ICD-electron and kinetic energy release spectra following the 2p(3/2) → 4s, 2p(1/2) → 4s and 2p(3/2) → 3d of Ar in ArKr and Ar2. We demonstrate that the presence of the chemically "softer" partner atom results in an increase in the energies of the emitted ICD electrons, and also in the appearance of additional ICD-active states. The latter leads to a threefold increase in the ICD yield for the case of the 2p(3/2, 1/2) → 4s parent core excitations.

Detecting ultrafast interatomic electronic processes in media by fluorescence

Interatomic coulombic decay (ICD), a radiationless transition in weakly bonded systems, such as solutes or van der Waals bound aggregates, is an effective source for electrons of low kinetic energy. So far, the ICD processes could only be probed in ultra-high vacuum by using electron and/or ion spectroscopy. Here we show that resonant ICD processes can also be detected by measuring the subsequently emitted characteristic fluorescence radiation, which makes their study in dense media possible.

Dissociation mechanisms of the Ar trimer induced by a third atom in high-energy electron-impact ionization

We experimentally studied the dissociation dynamics of a highly charged ${\text{Ar}}_{3}$ cluster initiated by a high-energy electron. The dissociation patterns of the correlated ions from a two-body and a three-body Coulombic explosion (CE) of (${\text{Ar}}_{3}$)${}^{2+}$ suggest that predissociation alters the evolution of radiative charge transfer. The three-body CE in (${\text{Ar}}_{3}$)${}^{4+}$ and (${\text{Ar}}_{3}$)${}^{5+}$ is driven, after double ionization of one constituent Ar atom, by single ionization with a simultaneous interatomic Coulombic decay process.

The Role of the Partner Atom and Resonant Excitation Energy in Interatomic Coulombic Decay in Rare Gas Dimers.

We provide experimental evidence for interatomic Coulombic decay (ICD) in mixed rare gas dimers following resonant Auger decay. A velocity map imaging apparatus together with a cooled supersonic beam containing Ar2 and NeAr dimers was used to record the energy and angular distributions of electrons in coincidence with two mass selected ions following the excitation of a number of resonances converging to the Ar 2p3/2–1 threshold using synchrotron radiation. It is shown that the ICD process can be controlled by the choice of the partner atom in the dimer or of the resonance that triggers the resonant Auger decay.

Interatomic Coulombic decay and electron-transfer-mediated decay following triple ionization in Ne2, NeAr, and Ar2

We report the first observation of electron-transfer-mediated decay (ETMD) and interatomic Coulombic decay (ICD) from the triply charged states with an inner-valence vacancy, using the Ne2, NeAr, and Ar2. These ETMD and ICD processes are unambiguously identified by electron-ion-ion coincidence spectroscopy in which the kinetic energy of the ETMD or ICD electron and the kinetic energy release between the two fragment ions are measured in coincidence.