Interatomic Coulombic electron capture from first principles

Interatomic Coulombic electron capture (ICEC) is an environment-assisted process in which a free electron can efficiently attach to an ion, atom or molecule by transferring the excess energy to a neighboring species. Absolute cross sections are necessary to evaluate the relative importance of this process. In this work, we employ the R-matrix method to compute ab initio these cross sections for a singly charged neon ion embedded in small helium clusters. Our results show that the ICEC cross sections are several orders of magnitude higher than anticipated and dominate other competing processes. Electron energy loss spectra on an absolute scale are provided for the Ne+@He20 cluster. Such spectra exhibit an unambiguous signature of the ICEC process. The finding is expected to stimulate experimental observations

The virtual photon approximation for three-body interatomic Coulombic decay

Interatomic Coulombic decay (ICD) is a mechanism which 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 ab initio 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)]. Here, we develop a virtual photon description of three-body ICD, showing that a mediator atom can have a significant influence at much larger distances. In this regime, this impact is due to the scattering of virtual photons off the mediator, allowing for simple analytical results and being manifest in a distinct geometry-dependence which includes interference effects. As a striking example, we show 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

On the computations of interatomic Coulombic decay widths with R-matrix method

Interatomic Coulombic Decay (ICD) is a general mechanism in which an excited atom can transfer its excess energy to a neighbor which is thus ionized. ICD belongs to the family of Feshbach resonance processes, and, as such, states undergoing ICD are characterized by their energy width. In this work, we investigate the computations of ICD widths using the R-matrix method as implemented in the UKRmol package. Helium dimer is used here as a benchmark system. The results are compared with those obtained with the well established Fano-Algebraic Diagrammatic Construction method. It is shown that the R-matrix method in its present implementation provides accurate total and partial widths if the kinetic energy of the ICD electron is lower than 10 eV. Advantages and limitations of the R-matrix method on the computations of ICD widths are discussed

Fano interferences in environment-enabled electron capture

Interatomic Coulombic electron capture (ICEC) is an environment-assisted process in which a free electron can efficiently attach to a quantum system by transferring the excess energy of the electron capture to a neighbor ionizing it. Using the ab initio R-matrix method, we show that Fano profiles, resulting from interferences between the ICEC final states and resonant states, appear in the ICEC cross sections even at extremely large system-neighbor separations. We identify several types of resonant states depending on their decay pathways which may involve long-range electron and energy transfer. ICEC is a fundamental process and the interferences lead to substantial enhancement or decrease of the cross sections. The present investigation is therefore of general relevance in many contexts wherever electron capture in an environment takes place

Electron attachment to a proton in water by interatomic Coulombic electron capture: An <i><b>R</b></i>-matrix study

Interatomic Coulombic electron capture (ICEC) is an environment-enabled electron capture process in which a free electron can efficiently attach to a quantum system by transferring the excess energy to a neighbor thus ionizing it. Using the ab initio R-matrix method, we investigate the electron attachment to a proton in the neighborhood of a water molecule. The corresponding ICEC cross sections exhibit clear Fano profiles, resulting from interferences between the ICEC final states and resonant states. These Fano interferences, observed in the total ICEC cross sections, were discussed in our recent work on large system-neighbor separations [A. Molle et al., Phys. Rev. A 103, 012808 (2021)]. In the present study, we report on the ICEC cross sections at shorter distances which are relevant in biological and biochemical contexts. Furthermore, we investigate the partial ICEC cross sections and demonstrate that the ionization of a water molecule via ICEC is substantially different from that due to direct photoionization. Finally, we show that the distortion of the equilibrium geometry of the water molecule due to the presence of the proton influences the ICEC process

Competition between proton transfer and intermolecular Coulombic decay in water

Intermolecular Coulombic decay (ICD) is a ubiquitous relaxation channel of electronically excited states in weakly bound systems, ranging from dimers to liquids. As it is driven by electron correlation, it was assumed that it will dominate over more established energy loss mechanisms, for example fluorescence. Here, we use electron–electron coincidence spectroscopy to determine the efficiency of the ICD process after 2a1 ionization in water clusters. We show that this efficiency is surprisingly low for small water clusters and that it gradually increases to 40–50% for clusters with hundreds of water units. Ab initio molecular dynamics simulations reveal that proton transfer between neighboring water molecules proceeds on the same timescale as ICD and leads to a configuration in which the ICD channel is closed. This conclusion is further supported by experimental results from deuterated water. Combining experiment and theory, we infer an intrinsic ICD lifetime of 12–52 fs for small water clusters

Hard-X-Ray-Induced Multistep Ultrafast Dissociation

Creation of deep core holes with very short (τ≤1  fs) lifetimes triggers a chain of relaxation events leading to extensive nuclear dynamics on a few- femtosecond time scale. Here we demonstrate a general multistep ultrafast dissociation on an example of HCl following Cl 1s→σ∗ excitation. Intermediate states with one or multiple holes in the shallower core electron shells are generated in the course of the decay cascades. The repulsive character and large gradients of the potential energy surfaces of these intermediates enable ultrafast fragmentation after the absorption of a hard x-ray photon

Etude théorique de phénomènes d'interférences au cours de collisions atomiques et moléculaires

PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Inner-valence Auger decay in hydrocarbon molecules

International audienceWe have theoretically studied the Auger effect after inner-valence ionization of several unsaturated and saturated cyclic and linear hydrocarbon molecules. These prototype molecules were chosen such that the effects of the different characteristics of aromaticity (π electrons, conjugation, cyclic geometry) on the Auger decay can be investigated separately. We show that among these molecules, the ones having π electrons can undergo Auger decay after inner-valence ionization. Furthermore, the results reported here suggest that conjugation allows for several open Auger decay channels while aromaticity limits the range of the latter

Interatomic Coulombic decay widths of helium trimer: A diatomics-in-molecules approach

International audienceWe report a new method to compute the Interatomic Coulombic Decay (ICD) widths for large clusters which relies on the combination of the projection-operator formalism of scattering theory and the diatomics-in-molecules approach. The total and partial ICD widths of a cluster are computed from the energies and coupling matrix elements of the atomic and diatomic fragments of the system. The method is applied to the helium trimer and the results are compared to fully ab initio widths. A good agreement between the two sets of data is shown. Limitations of the present method are also discussed