[1] Vasili Stumpf, Simona Scheit, Přemysl Kolorenč, and Kirill Gokhberg. Electron transfer mediated decay in NeXe triggered by K-LL Auger decay of Ne. CHEMICAL PHYSICS, 482(SI):192--200, JAN 12 2017. [ bib | DOI ]
In this article we present the results of an ab initio study of electron transfer mediated decay (ETMD) in NeXe dimer triggered by the K -LL Auger decay of Ne. We found that the Ne2+(2p(-2) D-1)Xe and Ne2+(2p(-2) S-1)Xe states which are strongly populated in the Auger process may decay by ETMD emitting a slow electron and leading to the Coulomb explosion of the dimer which results in Ne+ and Xe2+ ions. We also computed the corresponding decay widths, the ETMD electron spectra, and the kinetic energy release of the nuclei (KER) spectra. We showed that the spectra corresponding to the decaying states which derive from the two multiplets have completely different shape which reflects differing accessibility of the ETMD final states. Thus, in the Ne2+(2p(-2) S-1)Xe state ETMD is allowed for all interatomic distances accessible in nuclear dynamics, while in the Ne2+(2p(-2) D-1)Xe state the ETMD channels become closed one by one. This in turn leads to the different behavior of the ETMD decay widths and ultimately the spectra. We show how these differences make it possible to study ETMD of the two states separately in a coincident measurement. We also discuss how the dynamics which follow ETMD in the final state manifold may lead to the appearance of the unusual products: Ne, Xe3+ and a slow electron. (C) 2016 Elsevier B.V. All rights reserved.

[2] J. Rist, T. Miteva, B. Gaire, H. Sann, F. Trinter, M. Keiling, N. Gehrken, A. Moradmand, B. Berry, M. Zohrabi, M. Kunitski, I. Ben-Itzhak, A. Belkacem, T. Weber, A. L. Landers, M. Schoeffler, J. B. Williams, P. Kolorenč, K. Gokhberg, T. Jahnke, and R. Doerner. A comprehensive study of Interatomic Coulombic Decay in argon dimers: Extracting R-dependent absolute decay rates from the experiment. CHEMICAL PHYSICS, 482(SI):185--191, JAN 12 2017. [ bib | DOI ]
In this work we present a comprehensive and detailed study of Interatomic Coulombic Decay (ICD) occurring after irradiating argon dimers with XUV-synchrotron radiation. A manifold of different decay channels is observed and the corresponding initial and final states are assigned. Additionally, the effect of nuclear dynamics on the ICD electron spectrum is examined for one specific decay channel. The internuclear distance-dependent width Gamma(R) of the decay is obtained from the measured kinetic energy release distribution of the ions employing a classical nuclear dynamics model. (C) 2016 Elsevier B.V. All rights reserved.

[3] Přemysl Kolorenč, Vitali Averbukh, Raimund Feifel, and John Eland. Collective relaxation processes in atoms, molecules and clusters. JOURNAL OF PHYSICS B: ATOMIC MOLECULAR AND OPTICAL PHYSICS, 49(8):082001, 2016. [ bib | http ]
Electron correlation is an essential driver of a variety of relaxation processes in excited atomic and molecular systems. These are phenomena which often lead to autoionization typically involving two-electron transitions, such as the well-known Auger effect. However, electron correlation can give rise also to higher-order processes characterized by multi-electron transitions. Basic examples include simultaneous two-electron emission upon recombination of an inner-shell vacancy (double Auger decay) or collective decay of two holes with emission of a single electron. First reports of this class of processes date back to the 1960s, but their investigation intensified only recently with the advent of free-electron lasers. High fluxes of high-energy photons induce multiple excitation or ionization of a system on the femtosecond timescale and under such conditions the importance of multi-electron processes increases significantly. We present an overview of experimental and theoretical works on selected multi-electron relaxation phenomena in systems of different complexity, going from double Auger decay in atoms and small molecules to collective interatomic autoionization processes in nanoscale samples.

[4] Raimund Feifel, John H. D. Eland, Richard J. Squibb, Melanie Mucke, Sergey Zagorodskikh, Per Linusson, Francesco Tarantelli, Přemysl Kolorenč, and Vitali Averbukh. Ultrafast molecular three-electron auger decay. PHYSICAL REVIEW LETTERS, 116:073001, Feb 2016. [ bib | DOI | http ]
Three-electron Auger decay is an exotic and elusive process, in which two outer-shell electrons simultaneously refill an inner-shell double vacancy with emission of a single Auger electron. Such transitions are forbidden by the many-electron selection rules, normally making their decay lifetimes orders of magnitude longer than the few-femtosecond lifetimes of normal (two-electron) Auger decay. Here we present theoretical predictions and direct experimental evidence for a few-femtosecond three-electron Auger decay of a double inner-valence-hole state in CH3F. Our analysis shows that in contrast to double core holes, double inner-valence vacancies in molecules can decay exclusively by this ultrafast three-electron Auger process, and we predict that this phenomenon occurs widely.

[5] Nicolas Sisourat, Sévan Kazandjian, Aurélie Randimbiarisolo, and Přemysl Kolorenč. Interatomic coulombic decay widths of helium trimer: A diatomics-in-molecules approach. THE JOURNAL OF CHEMICAL PHYSICS, 144(8):084111, Feb 2016. [ bib | DOI | http ]
We 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.

[6] Přemysl Kolorenč and Nicolas Sisourat. Interatomic coulombic decay widths of helium trimer: Ab initio calculations. THE JOURNAL OF CHEMICAL PHYSICS, 143(22):224310, Dec 2015. [ bib | DOI ]
We report on an extensive study of interatomic Coulombic decay (ICD) widths in helium trimer computed using a fully ab initio method based on the Fano theory of resonances. Algebraic diagrammatic construction for one-particle Green's function is utilized for the solution of the many-electron problem. An advanced and universal approach to partitioning of the configuration space into discrete states and continuum subspaces is described and employed. Total decay widths are presented for all ICD-active states of the trimer characterized by one-site ionization and additional excitation of an electron into the second shell. Selected partial decay widths are analyzed in detail, showing how three-body effects can qualitatively change the character of certain relaxation transitions. Previously unreported type of three-electron decay processes is identified in one class of the metastable states. (C) 2015 AIP Publishing LLC.

[7] A. Sanchez-Gonzalez, T. R. Barillot, R. J. Squibb, P. Kolorenč, M. Agaker, V. Averbukh, M. J. Bearpark, C. Bostedt, J. D. Bozek, S. Bruce, S. Carron Montero, R. N. Coffee, B. Cooper, J. P. Cryan, M. Dong, J. H. D. Eland, L. Fang, H. Fukuzawa, M. Guehr, M. Ilchen, A. S. Johnsson, C. Liekhus-S, A. Marinelli, T. Maxwell, K. Motomura, M. Mucke, A. Natan, T. Osipov, C. Ostlin, M. Pernpointner, V. S. Petrovic, M. A. Robb, C. Sathe, E. R. Simpson, J. G. Underwood, M. Vacher, D. J. Walke, T. J. A. Wolf, V. Zhaunerchyk, J-E Rubensson, N. Berrah, P. H. Bucksbaum, K. Ueda, R. Feifel, L. J. Frasinski, and J. P. Marangos. Auger electron and photoabsorption spectra of glycine in the vicinity of the oxygen k-edge measured with an x-fel. JOURNAL OF PHYSICS B: ATOMIC MOLECULAR AND OPTICAL PHYSICS, 48(23):234004, DEC 14 2015. [ bib | DOI ]
We report the first measurement of the near oxygen K-edge auger spectrum of the glycine molecule. Our work employed an x-ray free electron laser as the photon source operated with input photon energies tunable between 527 and 547 eV. Complete electron spectra were recorded at each photon energy in the tuning range, revealing resonant and non-resonant auger structures. Finally ab initio theoretical predictions are compared with the measured above the edge auger spectrum and an assignment of auger decay channels is performed.

[8] Elke Fasshauer, Přemysl Kolorenč, and Markus Pernpointner. Relativistic decay widths of autoionization processes: The relativistic fanoadc-stieltjes method. THE JOURNAL OF CHEMICAL PHYSICS, 142(14):144106, APR 14 2015. [ bib | DOI ]
Electronic decay processes of ionized systems are, for example, the Auger decay or the Interatomic/Intermolecular Coulombic Decay. In both processes, an energetically low lying vacancy is filled by an electron of an energetically higher lying orbital and a secondary electron is instantaneously emitted to the continuum. Whether or not such a process occurs depends both on the energetic accessibility and the corresponding lifetime compared to the lifetime of competing decay mechanisms. We present a realization of the non-relativistically established FanoADC-Stieltjes method for the description of autoionization decay widths including relativistic effects. This procedure, being based on the Algebraic Diagrammatic Construction (ADC), was adapted to the relativistic framework and implemented into the relativistic quantum chemistry program package Dirac. It is, in contrast to other existing relativistic atomic codes, not limited to the description of autoionization lifetimes in spherically symmetric systems, but is instead also applicable to molecules and clusters. We employ this method to the Auger processes following the Kr3d(-1), Xe4d(-1), and Rn5d(-1) ionization. Based on the results, we show a pronounced influence of mainly scalar-relativistic effects on the decay widths of autoionization processes. (C) 2015 AIP Publishing LLC.

[9] Bridgette Cooper, Přemysl Kolorenč, Leszek J. Frasinski, Vitali Averbukh, and Jon P. Marangos. Analysis of a measurement scheme for ultrafast hole dynamics by few femtosecond resolution x-ray pump-probe auger spectroscopy. FARADAY DISCUSSIONS, 171:93--111, 2014. [ bib | DOI | http ]
Ultrafast hole dynamics created in molecular systems as a result of sudden ionisation is the focus of much attention in the field of attosecond science. Using the molecule glycine we show through ab initio simulations that the dynamics of a hole, arising from ionisation in the inner valence region, evolves with a timescale appropriate to be measured using X-ray pulses from the current generation of SASE free electron lasers. The examined pump-probe scheme uses X-rays with photon energy below the K edge of carbon (275-280 eV) that will ionise from the inner valence region. A second probe X-ray at the same energy can excite an electron from the core to fill the vacancy in the inner-valence region. The dynamics of the inner valence hole can be tracked by measuring the Auger electrons produced by the subsequent refilling of the core hole as a function of pump-probe delay. We consider the feasibility of the experiment and include numerical simulation to support this analysis. We discuss the potential for all X-ray pump-X-ray probe Auger spectroscopy measurements for tracking hole migration.

[10] T. Miteva, Y.-C. Chiang, P. Kolorenč, A. I. Kuleff, L. S. Cederbaum, and K. Gokhberg. The effect of the partner atom on the spectra of interatomic coulombic decay triggered by resonant auger processes. THE JOURNAL OF CHEMICAL PHYSICS, 141(16):164303, 2014. [ bib | DOI | http ]
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.

[11] T. Miteva, Y. C. Chiang, P. Kolorenč, A. I. Kuleff, K. Gokhberg, and L. S. Cederbaum. Interatomic coulombic decay following resonant core excitation of ar in argon dimer. THE JOURNAL OF CHEMICAL PHYSICS, 141(6):064307, AUG 14 2014. [ bib | DOI ]
A scheme utilizing excitation of core electrons followed by the resonant-Auger - interatomic Coulombic decay (RA-ICD) cascade was recently proposed as a means of controlling the generation site and energies of slow ICD electrons. This control mechanism was verified in a series of experiments in rare gas dimers. In this article, we present fully ab initio computed ICD electron and kinetic energy release spectra produced following 2p(3/2) -> 4s, 2p(1/2) -> 4s, and 2p(3/2) -> 3d core excitations of Ar in Ar-2. We demonstrate that the manifold of ICD states populated in the resonant Auger process comprises two groups. One consists of lower energy ionization satellites characterized by fast interatomic decay, while the other consists of slow decaying higher energy ionization satellites. We show that accurate description of nuclear dynamics in the latter ICD states is crucial for obtaining theoretical electron and kinetic energy release spectra in good agreement with the experiment. (C) 2014 AIP Publishing LLC.

[12] Kirill Gokhberg, Přemysl Kolorenč, Alexander I. Kuleff, and Lorenz S. Cederbaum. Site- and energy-selective slow-electron production through intermolecular coulombic decay. NATURE, 505(7485):661+, JAN 30 2014. [ bib | DOI ]
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.

[13] V. Stumpf, P. Kolorenč, K. Gokhberg, and L. S. Cederbaum. Efficient pathway to neutralization of multiply charged ions produced in auger processes. PHYSICAL REVIEW LETTERS, 110(25):258302, JUN 21 2013. [ bib | DOI ]
After core ionization of an atom or molecule by an x-ray photon, multiply charged ions are produced in the Auger decay process. These ions tend to neutralize their charge when embedded in an environment. We demonstrate that, depending on the atom or molecule and its neighbors, electron transfer mediated decay (ETMD) provides a particularly efficient neutralization pathway for the majority of the ions produced by Auger decay. The mechanism is rather general. As a showcase example, we conducted an ab initio study of the NeKr2 cluster after core ionization of the Ne atom. This example has been chosen because it is amenable to both ab initio calculations and coincidence experiments. We find that even for frozen nuclei, the neutralization rate can be as fast as 0.130 ps(-1). We also show that nuclear dynamics may increase the rate by about an order of magnitude. The generality of the mechanism makes this neutralization pathway important in weakly bonded environments.

[14] Nicolas Sisourat, Nikolai V. Kryzhevoi, Přemysl Kolorenč, Simona Scheit, and Lorenz S. Cederbaum. Giant interatomic coulombic decay. In ID Williams, HW VanDerHart, JF McCann, and DSF Crothers, editors, XXVII INTERNATIONAL CONFERENCE ON PHOTONIC, ELECTRONIC AND ATOMIC COLLISIONS (ICPEAC 2011), PTS 1-15, volume 388 of Journal of Physics Conference Series, page 012043, DIRAC HOUSE, TEMPLE BACK, BRISTOL BS1 6BE, ENGLAND, 2012. IOP PUBLISHING LTD. 27th International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC), Queens Univ Belfast, Belfast, NORTH IRELAND, JUL 27-AUG 02, 2011. [ bib | DOI ]
On the example of the giant helium dimer, we present an efficient electronic decay process for excited atoms or molecules embedded in a chemical environment, called Interatomic (intermolecular) Coulombic decay (ICD). After simultaneous ionization and excitation of a helium atom within a helium dimer, the excited ion relaxes by ICD to He+ (1s) and the neighbor neutral helium is ionized to He+ (1s) as well and emits a secondary electron. A short review on ab initio methods developed during the last 10 years to accurately describe ICD is reported. Finally, the main striking results on the helium dimer obtained experimentally and theoretically are summarized.

[15] Vitali Averbukh and Přemysl Kolorenč. Electronic decay in multiply charged polyatomic systems. In CA Nicolaides and E Brandas, editors, ADVANCES IN QUANTUM CHEMISTRY, VOL 63: UNSTABLE STATES IN THE CONTINUOUS SPECTRA, PT II - INTERPRETATION, THEORY AND APPLICATIONS, volume 63 of Advances in Quantum Chemistry, pages 309--342. ELSEVIER ACADEMIC PRESS INC, 525 B STREET, SUITE 1900, SAN DIEGO, CA 92101-4495 USA, 2012. [ bib | DOI ]
Inner-shell ionization of atoms, molecules, and clusters often leads to creation of highly excited ionic states that are embedded into double (or even multiple) ionization continua and decay by electron emission. The most common electronic decay process triggered by core ionization is known as Auger effect. The dynamics of the Auger decay is usually assumed to be exponential, and the process is characterized by a decay rate. The advent of the high-intensity x-ray free-electron lasers and their envisaged applications in molecular imaging have made it necessary to consider Auger-type processes in polyatomic systems under conditions of multiple ionization, both in the core and in the valence shells. Here, we review our recent theoretical work on the theory of electronic decay in multiply charged molecules and clusters. Particular attention is given to the effects of the spectator vacancies on the Auger decay rates, trapping of the Auger electron in a multiply charged system, and collective decay of two vacancies.

[16] Přemysl Kolorenč and Vitali Averbukh. K-shell auger lifetime variation in doubly ionized ne and first row hydrides. THE JOURNAL OF CHEMICAL PHYSICS, 135(13):134314, OCT 7 2011. [ bib | DOI ]
We consider 1s Auger decay in doubly (core-core and core-valence) ionized Ne and in the isoelectronic first row element hydrides. We show theoretically that the presence of the spectator inner valence vacancy leads to Auger lifetime variation of up to about a factor of 2, relative to the Auger lifetimes in the singly ionized species. The origin of this effect is traced to spin selection rules. Implications on the modelling of the radiation damage in strong x-ray fields are discussed. (C) 2011 American Institute of Physics. [doi:10.1063/1.3646204]

[17] V. Averbukh, Ph. V. Demekhin, P. Kolorenč, S. Scheit, S. D. Stoychev, A. I. Kuleff, Y. C. Chiang, K. Gokhberg, S. Kopelke, N. Sisourat, and L. S. Cederbaum. Interatomic electronic decay processes in singly and multiply ionized clusters. JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA, 183(1-3, SI):36--47, JAN 2011. [ bib | DOI ]
Since their theoretical prediction in 1997, interatomic (intermolecular)Coulombic decay (ICD) and relatedprocesses have been in the focus of intensive theoretical and experimental research. The spectacular progress in this direction has been stimulated both by the fundamental importance of the discovered electronic decay phenomena and by the exciting possibility of their practical application, for example in spectroscopy of interfaces. Interatomic decay phenomena take place in inner-shell-ionized clusters due to electronic correlation between two or more cluster constituents. These processes lead to the decay of inner-shell vacancies by electron emission and often also to disintegration of the resulting multiply ionized cluster. Here we review the recent progress in the study of interatomic decay phenomena in singly and multiply ionized clusters. (C) 2010 Elsevier B.V. All rights reserved.

[18] Nicolas Sisourat, Nikolai V. Kryzhevoi, Přemysl Kolorenč, Simona Scheit, and Lorenz S. Cederbaum. Impact of nuclear dynamics on interatomic coulombic decay in a he dimer. PHYSICAL REVIEW A, 82(5):053401, NOV 3 2010. [ bib | DOI ]
After simultaneous ionization and excitation of one helium atom within the giant weakly bound helium dimer, the excited ion can relax via interatomic Coulombic decay (ICD) and the excess energy is transferred to ionize the neighboring helium atom. We showed [Sisourat et al. Nature Phys. 6, 508 (2010)] that the distributions of the kinetic energy released by the two ions reflect the nodal structures of the ICD-involved vibrational wave functions. We also demonstrated that energy transfer via ICD between the two helium atoms can take place over more than 14 angstrom. We report here a more detailed analysis of the ICD process and of the impact of the nuclear dynamics on the electronic decay. Nonadiabatic effects during the ICD process and the accuracy of the potential energy curve of helium dimer and of the computed decay rates are also investigated.

[19] Nicolas Sisourat, Hendrik Sann, Nikolai V. Kryzhevoi, Přemysl Kolorenč, Tilo Havermeier, Felix Sturm, Till Jahnke, Hong-Keun Kim, Reinhard Doerner, and Lorenz S. Cederbaum. Interatomic electronic decay driven by nuclear motion. PHYSICAL REVIEW LETTERS, 105(17):173401, OCT 22 2010. [ bib | DOI ]
The interatomic electronic decay after inner-valence ionization of a neon atom by a single photon in a neon-helium dimer is investigated. The excited neon atom relaxes via interatomic Coulombic decay and the excess energy is transferred to the helium atom and ionizes it. We show that the decay process is only possible if the dimer's bond stretches up to 6.2 angstrom, i.e., to more than twice the equilibrium interatomic distance of the neutral dimer. Thus, it is demonstrated that the electronic decay, taking place at such long distances, is driven by the nuclear motion.

[20] Přemysl Kolorenč, Nikolai V. Kryzhevoi, Nicolas Sisourat, and Lorenz S. Cederbaum. Interatomic coulombic decay in a he dimer: Ab initio potential-energy curves and decay widths. PHYSICAL REVIEW A, 82(1):013422, JUL 28 2010. [ bib | DOI ]
The energy gained by either of the two helium atoms in a helium dimer through simultaneous ionization and excitation can be efficiently transferred to the other helium atom, which then ionizes. The respective relaxation process called interatomic Coulombic decay (ICD) is the subject of the present paper. Specifically, we are interested in ICD of the lowest of the ionized excited states, namely, the He(+)(n = 2) He states, for which we calculated the relevant potential-energy curves and the interatomic decay widths. The full-configuration interaction method was used to obtain the potential-energy curves. The decay widths were computed by utilizing the Fano ansatz, Green's- function methods, and the Stieltjes imaging technique. The behavior of the decay widths with the interatomic distance is examined and is elucidated, whereby special emphasis is given to the asymptotically large interatomic separations. Our calculations show that the electronic ICD processes dominate over the radiative decay mechanisms over a wide range of interatomic distances. The ICD in the helium dimer has recently been measured by Havermeier et al. [Phys. Rev. Lett. 104, 133401 (2010)]. The impact of nuclear dynamics on the ICD process is extremely important and is discussed by Sisourat et al. [Nat. Phys. 6, 508 (2010)] based on the ab initio data computed in the present paper.

[21] Nicolas Sisourat, Nikolai V. Kryzhevoi, Přemysl Kolorenč, Simona Scheit, Till Jahnke, and Lorenz S. Cederbaum. Ultralong-range energy transfer by interatomic coulombic decay in an extreme quantum system. NATURE PHYSICS, 6(7):508--511, JUL 2010. [ bib | DOI ]
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 operative(1). 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 clusters(2-5) as well as in hydrogen-bonded systems(6-8). 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.

[22] J. Fedor, C. Winstead, V. McKoy, M. Čížek, K. Houfek, P. Kolorenč, and J. Horáček. Electron scattering in hcl: An improved nonlocal resonance model. PHYSICAL REVIEW A, 81(4):042702, APR 2010. [ bib | DOI ]
We present an improved nonlocal resonance model for electron-HCl collisions. The short-range part of the model is fitted to ab initio electron-scattering eigenphase sums calculated using the Schwinger multichannel method, while the long-range part is based on the ab initio potential-energy curve of the bound anion HCl(-). This model significantly improves the agreement of nonlocal resonance calculations with recent absolute experimental data on dissociative electron attachment cross sections for HCl and DCl. It also partly resolves an inconsistency in the temperature effect in dissociative electron attachment to HCl present in the literature. Finally, the present model reproduces all qualitative structures observed previously in elastic scattering and vibrational-excitation cross sections.

[23] K. Gokhberg, S. Kopelke, N. V. Kryzhevoi, P. Kolorenč, and L. S. Cederbaum. Dependence of interatomic decay widths on the symmetry of the decaying state: Analytical expressions and ab initio results. PHYSICAL REVIEW A, 81(1):013417, JAN 2010. [ bib | DOI ]
In this article, we investigate the dependence of interatomic Coulombic decay widths on the symmetry of the decaying state. In this type of decay, excited, ionized, and doubly ionized states of an atom or molecule can efficiently relax by ionizing their environment. We concentrate on an atom A and a neighboring atom B and consider such excited, ionized, or doubly ionized states of A that decay by emitting a single photon if A were an isolated atom. Analytical expressions for the various widths are derived for large interatomic distances R. A pronounced dependence of the widths on the symmetry properties of the decaying state is found. This dependence at large R is related to the dependence of the interaction energy of two classical dipoles on their mutual orientation. Comparison with precise ab initio calculations shows that the analytical results hold well at large R, while they deviate from the ab initio values at smaller R due to the effect of orbital overlap.

[24] Vitali Averbukh and Přemysl Kolorenč. Collective interatomic decay of multiple vacancies in clusters. PHYSICAL REVIEW LETTERS, 103(18):183001, OCT 30 2009. [ bib | DOI ]
We predict that inner-shell ionization of more than one atom (or molecule) in a cluster, e.g., by intense free-electron laser radiation, can lead to an interatomic decay process in which the formed vacancy states decay simultaneously, while a neighboring neutral species is ionized. This collective decay phenomenon can be regarded as a transfer of two or more virtual photons from the ionized cluster units to a neutral one. Simulations of collective decay in (4(s)(-1), 4(s)(-1)) (Kr(+))(2)Ar show that the two-virtual-photon process can be competitive with the dissociative nuclear dynamics of the doubly ionized cluster. Generality of the collective interatomic decay is discussed.

[25] Ph. V. Demekhin, Y. C. Chiang, S. D. Stoychev, P. Kolorenč, S. Scheit, A. I. Kuleff, F. Tarantelli, and L. S. Cederbaum. Interatomic coulombic decay and its dynamics in near following k-ll auger transition in the ne atom. THE JOURNAL OF CHEMICAL PHYSICS, 131(10):104303, SEP 14 2009. [ bib | DOI ]
We analyze in detail the accessible relaxation pathways via electron emission of the Ne(2+)Ar states populated via the K-LL Auger decay of Ne(+)(1s(-1))Ar. In particular, we concentrate on the “direct” interatomic Coulombic decay (ICD) of the Ne(2+)(2s(-1)2p(-1))Ar weakly bound doubly ionized states into the manifold of the Ne(2+)(2p(-2))-Ar(+)(3p(-1)) repulsive triply ionized ones. To carry out the present study the potential energy curves of the NeAr ground state, the core ionized state Ne(+)(1s(-1))Ar, the relevant dicationic and tricationic states, and the corresponding ICD transition rates have been computed using accurate ab initio methods and basis sets. The total and partial ICD electron spectra are computed within the framework of the time-dependent theory of wave packet propagation. Thereby, the impact of nuclear dynamics accompanying the electronic decay on the computed ICD-electron spectra is investigated in detail. (C) 2009 American Institute of Physics. [doi:10.1063/1.3211114]

[26] V. Averbukh, P. Kolorenč, K. Gokhberg, and L. S. Cederbaum. Quantum chemical approach to interatomic decay rates in clusters. In P Piecuch, J Maruani, G DelgadoBarrio, and S Wilson, editors, ADVANCES IN THE THEORY OF ATOMIC AND MOLECULAR SYSTEMS: DYNAMICS, SPECTROSCOPY, CLUSTERS, AND NANOSTRUCTURES, volume 20 of Progress in Theoretical Chemistry and Physics, pages 155--181. Michigan State Univ, James B Henry Ctr, Execut Dev, 2009. 13th International Workshop on Quantum Systems in Chemisty and Physics, E Lansing, MI, JUL 06-12, 2008. [ bib | DOI ]
Since their theoretical prediction in 1997, interatomic (intermolecular) Coulombic decay (ICD) and related processes have been in the focus of intensive theoretical and experimental research. The spectacular progress in this direction has been stimulated both by the fundamental importance of the discovered electronic decay phenomena and by the exciting possibility of their practical application, for example, in spectroscopy of interfaces. Interatomic decay phenomena take place in inner-shell-ionized clusters due to electronic correlation between two or more cluster constituents. These processes lead to the decay of inner-shell vacancies by electron emission and often also to the disintegration of the resulting multiple ionized cluster. The primary objective of the theory is, thus, to predict the kinetic energy spectra of the emitted electrons and of the cluster fragments. These spectra are determined by an interplay between the electronic decay process and the nuclear dynamics. Key to the reliable prediction of the observable quantities is the knowledge of the time scale of the interatomic decay. Here we review the recent progress in the development of ab initio quantum chemical methods for the calculation of interatomic decay rates in excited, singly ionized, and doubly ionized systems as well as some of their applications, e.g., to rare gas systems and to endohedral fullerenes.

[27] Přemysl Kolorenč, Vitali Averbukh, Kirill Gokhberg, and Lorenz S. Cederbaum. Ab initio calculation of interatomic decay rates of excited doubly ionized states in clusters. THE JOURNAL OF CHEMICAL PHYSICS, 129(24):244102, DEC 28 2008. [ bib | DOI ]
Recently, a computational technique for ab initio calculation of the interatomic and intermolecular nonradiative decay processes has been developed [V. Averbukh and L. S. Cederbaum, J. Chem. Phys. 123, 204107 (2005)]. It combines the Fano formalism with the Green's function method known as the algebraic diagrammatic construction. The problem of normalization of continuum wave functions stemming from the use of the Gaussian basis sets is solved by using the Stieltjes imaging technique. In the present paper, the methodology is extended in order to describe the interatomic decay of excited doubly ionized states of clusters. The new computational scheme is applied to compute the interatomic decay rates of doubly ionized states formed by Auger relaxation of core vacancies in NeAr and MgNe van der Waals clusters.

[28] Miroslav Šulc, Přemysl Kolorenč, Michal Tarana, and Jiří Horáček. Fast and efficient solution of scattering integral equations. In TE Simos and G Maroulis, editors, SELECTED PAPERS FROM ICNAAM 2007 AND ICCMSE 2007, volume 1046 of AIP CONFERENCE PROCEEDINGS, pages 142--145, 2008. International Conference on Computational Methods in Science and Engineering, Corfu, GREECE, SEP 25, 2008-SEP 30, 2009. [ bib ]
In this work we propose a method for numerical treatment of integral equations describing scattering of low-energy electrons with atoms and molecules. The method is based on a combination of R-matrix approach with the Schwinger-Lanczos method proposed by the authors. It is shown on the example of scattering of electrons by hydrogen atoms in the static exchange approximation that the method is very fast, economic and very accurate. By using only 64 meshpoints the accuracy of 9 significant figures can be easily obtained.

[29] J. Fedor, M. Cingel, J. D. Skalny, P. Scheier, T. D. Maerk, M. Čížek, P. Kolorenč, and J. Horáček. Dissociative electron attachment to hbr: A temperature effect. PHYSICAL REVIEW A, 75(2):022703, FEB 2007. [ bib | DOI ]
The effects of rovibrational temperature on dissociative electron attachment to hydrogen bromide has been investigated from the experimental and theoretical point of view. Theoretical calculations based on the nonlocal resonance model predict a strong temperature effect on the Br- fragment ion yield due to population of higher vibrational and rotational states. A crossed beam experimental setup consisting of a temperature controlled effusive molecular beam and a trochoidal electron monochromator has been used to confirm this prediction. The high degree of agreement between experiment and theory indicates the validity of the theoretical model and its underlying physical picture.

[30] Jiří Horáček, Martin Čížek, Karel Houfek, and Přemysl Kolorenč. Long-lived states of molecular hydrogen anion. In E Roueff, editor, Atomic and Molecular Data and Their Applications, volume 901 of AIP CONFERENCE PROCEEDINGS, pages 147--155. Consell Sci Observ Paris; Observ Paris, Dept LUTh; Observ Paris, Dept LERMA; CNRS; Programme Natl Phys & Chimie Milleu Interstellaire; Programme Natl Planetol; Programme Natl Phys Stellaire; Assoc Euratom CEA; Inst Lasers & Plasmas; Reg Ile France, 2007. 5th International Conference on Atomic and Molecular Data and Their Applications, Meudon, FRANCE, OCT 15-NOV 19, 2006. [ bib ]
The existence of long-lived states (of the order of microseconds) of the molecular hydrogen anion H-2(-) is discussed both from theoretical and experimental points of view. The history of experimental search for these states is briefly reviewed and a theoretical explanation based on the use of the nonlocal resonance model offered. Final unambiguous confirmation of the existence by means of the accelerator mass spectrometry and mass spectrometry and the measurement of their lifetimes in electrostatic ion-beam trap is described.

[31] Přemysl Kolorenč and Jiří Horáček. Dissociative electron attachment and vibrational excitation of the chlorine molecule. PHYSICAL REVIEW A, 74(6):062703, DEC 2006. [ bib | DOI ]
This paper is aimed at the theoretical investigation of the inelastic processes taking place in resonant collisions of low-energy electrons with the chlorine molecule. Dissociative electron attachment and vibrational excitation of Cl-2 by electron impact is investigated in the energy range 0-1.5 eV, where the (2)Sigma(+)(u) resonance plays the central role. The calculations were carried out within the framework of the nonlocal resonance model. This approach makes it possible to calculate the integrated cross sections of the above-mentioned processes for a variety of initial and final rovibrational states of the target molecule. The present model is constructed on the basis of ab initio fixed-nuclei R-matrix calculations using the so-called Feshbach-Fano R-matrix method. The Schwinger-Lanczos algorithm was utilized to solve the Lippmann-Schwinger equation describing the motion of the nuclei.

[32] J Horáček, M Čížek, K Houfek, P Kolorenč, and W Domcke. Dissociative electron attachment and vibrational excitation of h-2 by low-energy electrons: Calculations based on an improved nonlocal resonance model. ii. vibrational excitation. PHYSICAL REVIEW A, 73(2):022701, FEB 2006. [ bib | DOI ]
We treat vibrational excitation of hydrogen by low-energy electrons using an improved nonlocal resonance model. The model is based on accurate ab initio data for the (2)Sigma(+)(u) shape resonance and takes full account of the nonlocality of the effective potential for nuclear motion. Integral vibrational excitation cross sections were calculated for numerous initial and final rovibrational states of the hydrogen molecule, and the dependence of the vibrational excitation cross section on the rovibrational initial target state has been investigated. The vibrational excitation cross sections are in very good agreement with measurements for the transitions v=0 -> 1 and v=0 -> 2, while for higher vibrational channels the agreement is less satisfactory. However, the oscillatory structures in v=0 -> 4 vibrational excitation and higher channels predicted by Domcke and collaborators and measured by Allan are described by the present calculation, in very good agreement with the experimental data. A detailed analysis of the origin of the oscillations has been performed. It is shown that the oscillations can be qualitatively understood within the so-called boomerang model of Herzenberg. The resonance contribution to the vibrationally elastic scattering (v -> v) is also discussed. It is found that this cross section is dominated at low energies by the resonance contribution, as predicted by Schulz. The calculated integral vibrational excitation cross sections generally are in good agreement with other theoretical data obtained by different approaches. A comprehensive study of the effect of isotopic substitution has been performed, and an inverse isotope effect in vibrational excitation has been found for certain vibrational levels of the target.

[33] J Horáček, M Čížek, P Kolorenč, and W Domcke. Isotope effects in vibrational excitation and dissociative electron attachment of dcl and dbr. EUROPEAN PHYSICAL JOURNAL D, 35(2):225--230, AUG 2005. [ bib | DOI ]
The results of calculations of vibrational excitation and dissociative electron attachment cross-sections of DCl and DBr are reported. The calculations are based on the nonlocal resonance model for electron-HCl/HBr scattering. The cross-sections for many initial rovibrational target states were calculated both for the hydrogenated and the deuterated compounds. The calculations reveal an unexpected result: the vibrational excitation cross-section of the deuterated molecule may in some cases be (significantly) larger than that of the hydrogenated compound. This effect is observed when the target molecule is initially excited to a vibrational state the energy of which is close to the threshold of dissociative attachment. Rotational excitation of the target molecule plays a similar role. Isotope effects in dissociative electron attachment are also discussed.

[34] P Kolorenč, V Brems, and J Horáček. Computing resonance positions, widths, and cross sections via the feshbach-fano r-matrix method: Application to potential scattering. PHYSICAL REVIEW A, 72(1, Part a-b):012708, JUL 2005. [ bib | DOI ]
The general Feshbach-Fano R-matrix procedure proposed recently by Nestmann [J. Phys. B 31, 3929 (1998)] makes it possible to construct resonance metastable states of transient molecular ions and their coupling elements to the background scattering continuum. These quantities are needed for the study of nuclear dynamics in the framework of the nonlocal resonance model. The performance of this approach is carefully studied and its properties analyzed in the field of potential scattering. An improvement of the Nestmann procedure which makes the calculation more stable and robust is proposed.

[35] J Horáček, M Čížek, K Houfek, P Kolorenč, and W Domcke. Dissociative electron attachment and vibrational excitation of h-2 by low-energy electrons: Calculations based on an improved nonlocal resonance model. PHYSICAL REVIEW A, 70(5):052712, NOV 2004. [ bib | DOI ]
An improved nonlocal resonance model proposed by Čížek, Horáček, and Domcke [J. Phys. B 31, 2571 (1998)] is used for the calculation of cross sections of electron dissociative attachment and vibrational excitation of molecular hydrogen by the impact of low-energy electrons in the range of (2)Sigma(u)(+) resonance. The model is based on ab initio data and takes full account of the nonlocality of the effective potential for the nuclear motion. The dissociative attachment cross sections and rate constants are calculated for all target states (v,J) of relevance and compared with other theoretical and experimental data. It is found that the present dissociative attachment cross section calculated under the conditions of the experiment carried out by Schulz and Asundi reproduces the larger of the two values proposed by them, i.e.-2.8x10(-21) cm(2). A detailed discussion of the dissociative attachment cross section as a function of the vibrational and rotational target states is given. Very narrow peaks, with a width of 1 meV, are observed in the dissociative attachment cross section for large values of the orbital quantum number J. These structures are interpreted as shape resonances in H-+H collision dynamics. It is shown that for large values of J rotational excitation of the hydrogen molecule enhances the dissociative attachment more efficiently than vibrational excitation. The largest dissociative attachment cross section of 28.3x10(-16) cm(2) is obtained for v=1 and J=29. The process of vibrational excitation will be discussed in a separate paper.

[36] J Horáček, M Čížek, K Houfek, P Kolorenč, and L Pichl. Resonance contributions to low-energy electron collisions with molecular hydrogen. NUKLEONIKA, 48(2):109--112, 2003. 2nd International Symposium on Low Energy Electron-Molecule Interactions, CHLEWISKA SIEDLCE, POLAND, AUG 29-SEP 02, 2002. [ bib ]
Calculations of electron dissociative attachment and vibrational excitation of molecular hydrogen by low-energy electrons based on an improved nonlocal resonance model are reported. The role of the rotational excitation of the target molecules is discussed.

[37] P Kolorenč, M Čížek, J Horáček, G Mil'nikov, and H Nakamura. Study of dissociative electron attachment to hi molecule by using r-matrix representation for green's function. PHYSICA SCRIPTA, 65(4):328--335, APR 2002. [ bib | DOI ]
The new method of calculation of scattering Green's function recently proposed by the authors (G. M. Mil'nikov. H. Nakamura, and J. Horáček. Comp. Phys. Comm. 135, 278 (2001)) is applied to the process of dissociative attachment of low-energy electrons to HI molecule previously considered by Horáček, Domcke and Nakamura (Z. Phys, D 42, 181 (1997)). The calculation is extended to vibrationally and rotationally excited target gas molecules. The temperature dependence of the dissociative attachment cross section is determined.

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