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1.
Phys Rev Lett ; 123(21): 213001, 2019 Nov 22.
Artigo em Inglês | MEDLINE | ID: mdl-31809166

RESUMO

We report the observation of the radiative decay of singly charged noble gas ground-state ions embedded in heterogeneous van der Waals clusters. Electron-photon coincidence spectroscopy and dispersed photon spectroscopy are applied to identify the radiative charge transfer from Kr atoms to a Ne_{2}^{+} dimer, which forms after single valence photoionization of Ne atoms at the surface of a NeKr cluster. This mechanism might be a fundamental decay process of ionized systems in an environment.

2.
J Chem Phys ; 151(18): 184305, 2019 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-31731862

RESUMO

Using electron spectroscopy, we investigated the nanoplasma formation process generated in xenon clusters by intense soft x-ray free electron laser (FEL) pulses. We found clear FEL intensity dependence of electron spectra. Multistep ionization and subsequent ionization frustration features are evident for the low FEL-intensity region, and the thermal electron emission emerges at the high FEL intensity. The present FEL intensity dependence of the electron spectra is well addressed by the frustration parameter introduced by Arbeiter and Fennel [New J. Phys. 13, 053022 (2011)].

3.
J Chem Phys ; 151(8): 084314, 2019 Aug 28.
Artigo em Inglês | MEDLINE | ID: mdl-31470702

RESUMO

Charge transfer (CT) at avoided crossings of excited ionized states of argon dimers is observed using a two-color pump-probe experiment at the free-electron laser in Hamburg (FLASH). The process is initiated by the absorption of three 27-eV-photons from the pump pulse, which leads to the population of Ar2+*-Ar states. Due to nonadiabatic coupling between these one-site doubly ionized states and two-site doubly ionized states of the type Ar+*-Ar+, CT can take place leading to the population of the latter states. The onset of this process is probed by a delayed infrared (800 nm) laser pulse. The latter ionizes the dimers populating repulsive Ar2+ -Ar+ states, which then undergo a Coulomb explosion. From the delay-dependent yields of the obtained Ar2+ and Ar+ ions, the lifetime of the charge-transfer process is extracted. The obtained experimental value of (531 ± 136) fs agrees well with the theoretical value computed from Landau-Zener probabilities.

4.
J Chem Phys ; 150(16): 164309, 2019 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-31042888

RESUMO

Electron transfer mediated decay (ETMD) is a process responsible for double ionization of dopants in He droplets. It is initiated by producing He+ in the droplet, which is neutralized by ETMD, and has been shown to strongly enhance the dopant's double ionization cross section. The efficiency of ETMD, the spectra of emitted secondary electrons, and the character of the ionic products depend on the nuclear dynamics during the decay. To date, there has been no theoretical investigation of multimode dynamics which accompanies ETMD, which could help to understand such dynamics in a He droplet. In this article, we consider the He-Li2 cluster where an ab initio examination of multimode dynamics during the electronic decay is feasible. Moreover, this cluster can serve as a minimal model for Li2 adsorbed on the droplet's surface-a system where ETMD can be observed experimentally. In He droplets, Li2 can be formed in both the ground X1Σg + and the first excited a3Σu + states. In this article, we present ab initio potential energy surfaces of the electronic states of the He-Li2 cluster involved in ETMD, as well as the respective decay widths. We show that the structure of these surfaces and expected nuclear dynamics strongly depend on the electronic state of Li2. Thus, the overall decay rate and the appearance of the observable electron spectra will be dictated by the electronic structure of the dopant.

5.
Nat Commun ; 10(1): 2186, 2019 05 16.
Artigo em Inglês | MEDLINE | ID: mdl-31097703

RESUMO

The increasing availability of X-ray free-electron lasers (XFELs) has catalyzed the development of single-object structural determination and of structural dynamics tracking in real-time. Disentangling the molecular-level reactions triggered by the interaction with an XFEL pulse is a fundamental step towards developing such applications. Here we report real-time observations of XFEL-induced electronic decay via short-lived transient electronic states in the diiodomethane molecule, using a femtosecond near-infrared probe laser. We determine the lifetimes of the transient states populated during the XFEL-induced Auger cascades and find that multiply charged iodine ions are issued from short-lived (∼20 fs) transient states, whereas the singly charged ones originate from significantly longer-lived states (∼100 fs). We identify the mechanisms behind these different time scales: contrary to the short-lived transient states which relax by molecular Auger decay, the long-lived ones decay by an interatomic Coulombic decay between two iodine atoms, during the molecular fragmentation.

6.
J Chem Phys ; 146(10): 104305, 2017 Mar 14.
Artigo em Inglês | MEDLINE | ID: mdl-28298097

RESUMO

The ultrafast transfer of excitation energy from one atom to its neighbor is observed in singly charged argon dimers in a time-resolved extreme ultraviolet (XUV)-pump IR-probe experiment. In the pump step, bound 3s-hole states in the dimer are populated by single XUV-photon ionization. The excitation-energy transfer at avoided crossings of the potential-energy curves leads to dissociation of the dimer, which is experimentally observed by further ionization with a time-delayed IR-probe pulse. From the measured pump-probe delay-dependent kinetic-energy release of coincident Ar+ + Ar+ ions, we conclude that the transfer of energy occurs on a time scale of about 800fs. This mechanism represents a fast relaxation process below the energy threshold for interatomic Coulombic decay.

7.
J Chem Phys ; 144(16): 164307, 2016 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-27131550

RESUMO

The impact of the solvent on the photodissociation of embedded molecules has been intensively investigated in the last decades. Collisions of photofragments with the solvating atoms or molecules can change their kinetic energy distribution or even lead to the de-excitation of the dissociating molecule to a bound electronic state quenching the dissociation. In this article we show that this cage effect is strongly enhanced if interatomic Coulombic decay (ICD) of the excited state becomes allowed. Ab initio calculations in H2O-Cl(-) cluster show that the ultra-fast dissociation of water in the à excited state is strongly quenched by ICD. We found that this very efficient quenching is due to two factors. First, the lifetimes of the à state due to ICD are short ranging between 6 and 30 fs. Second, nuclear dynamics is dominated by the chattering motion of the H atom between O and Cl(-) allowing ICD to act for longer times. We hope that this work will be an important first step in clarifying the impact of ICD on photodissociation of embedded molecules.

8.
Phys Chem Chem Phys ; 17(34): 22160-9, 2015 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-26256039

RESUMO

The X-ray absorption spectra (XAS) of Ar2 and ArNe dimers and small Ar clusters in the L2,3 region (244-252 eV) of the Ar atom have been recorded using synchrotron light and a combination of coincidence methods and kinetic energy discrimination of energetic ions. The absorption peaks in the spectra of the dimers and clusters were found to be shifted and broadened relative to the peaks in the spectrum of the Ar atom. In order to unambiguously relate these chemical shifts to the electronic structure of the core excited states in dimers, we performed ab initio calculations of the XAS spectra. Implications of the results for the use of XAS as a structure determination method in large rare gas clusters are discussed.

9.
J Chem Phys ; 140(20): 204320, 2014 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-24880293

RESUMO

Ionization satellites are key ingredients in the control of post ionization processes such as molecular dissociation and interatomic Coulombic decay. Here, using the high-level ab initio method of multi-reference configuration interaction up to triple excitations, we study the potential energy curves (PECs) of the ionization satellites of the ArHe dimer. With this model system, we demonstrate that the simple model used in alkaline earth metal and rare gas complexes to describe the satellites as a Rydberg electron moving on top of a dicationic core does not fully hold for the rare gas clusters. The more complex valence structure in the rare gas atom leads to the mixing of different electronic configurations of the dimer. This prevents one from assigning a single dicationic parent state to some of the ionization satellites. We further analyze the structure of the different PECs, demonstrating how the density of the Rydberg electron is reflected in the structure of the PEC wherever the simple model is applicable.

10.
Nature ; 505(7485): 661-3, 2014 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-24362566

RESUMO

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 (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. 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.

11.
J Chem Phys ; 138(1): 014305, 2013 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-23298039

RESUMO

In this work we investigate interatomic electronic decay processes taking place in mixed argon-xenon clusters upon the inner-valence ionization of an argon center. We demonstrate that both interatomic Coulombic decay and electron-transfer mediated decay (ETMD) are important in larger rare gas clusters as opposed to dimers. Calculated secondary electron spectra are shown to depend strongly on the spin-orbit coupling in the final states of the decay as well as the presence of polarizable environment. It follows from our calculations that ETMD is a pure interface process taking place between the argon-xenon layers. The interplay of all these effects is investigated in order to arrive at a suitable physical model for the decay of inner-valence vacancies taking place in mixed ArXe clusters.

12.
J Chem Phys ; 135(14): 144112, 2011 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-22010703

RESUMO

In this work we demonstrate that the interatomic Coulombic decay (ICD), an ultrafast electron relaxation process known for atoms and molecules, is possible in general binding potentials. We used the multiconfiguration time-dependent Hartree method for fermions to study ICD in real time in a two-electron model system of two potential wells. Two decay channels were identified and analyzed by using the box stabilization analysis as well as by evaluating the autocorrelation function and measuring the outgoing electron flux during time-propagations. The total and partial ICD widths of an excited state localized in one potential well as a function of the distance between the two potentials was obtained. Finally, we discuss the results with a view to a possible application of ICD in quantum dot technology.

13.
Phys Rev Lett ; 105(4): 043004, 2010 Jul 23.
Artigo em Inglês | MEDLINE | ID: mdl-20867842

RESUMO

An ultrafast mechanism belonging to the family of interatomic Coulombic decay (ICD) phenomena is proposed. When two excited species are present, an ultrafast energy transfer can take place bringing one of them to its ground state and ionizing the other one. It is shown that if large homoatomic clusters are exposed to an ultrashort and intense laser pulse whose photon energy is in resonance with an excitation transition of the cluster constituents, the large majority of ions will be produced by this ICD mechanism rather than by two-photon ionization. A related collective-ICD process that is operative in heteroatomic systems is also discussed.

14.
J Chem Phys ; 129(24): 244102, 2008 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-19123490

RESUMO

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.

15.
J Chem Phys ; 124(14): 144315, 2006 Apr 14.
Artigo em Inglês | MEDLINE | ID: mdl-16626204

RESUMO

In an isolated atom, excitation of an inner valence electron above the outer valence subshell leads to creation of an autoionizing state. Recently, it has been demonstrated experimentally that in a cluster, the inner-valence-excited states can decay also by an interatomic mechanism which has been called resonant interatomic Coulombic decay (RICD). Here we show that RICD is indeed the leading but not the only possible interatomic decay mode of the inner-valence excitations in clusters. Using Ne (2s-->3p) excitation in MgNe cluster as an example, we explore the possible decay mechanisms and draw conclusions on their relative importance and on the nature of the corresponding decay products.

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