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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(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.

3.
Phys Rev Lett ; 122(15): 153401, 2019 Apr 19.
Artigo em Inglês | MEDLINE | ID: mdl-31050514

RESUMO

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 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)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 ab initio 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.

4.
Nat Commun ; 9(1): 4988, 2018 11 26.
Artigo em Inglês | MEDLINE | ID: mdl-30478319

RESUMO

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.

5.
J Phys Chem Lett ; 9(15): 4457-4462, 2018 Aug 02.
Artigo em Inglês | MEDLINE | ID: mdl-30020787

RESUMO

X-ray absorption and Auger electron spectroscopies are demonstrated to be powerful tools to unravel the electronic structure of solvated ions. In this work for the first time, we use a combination of these methods in the tender X-ray regime. This allowed us to address electronic transitions from deep core levels, to probe environmental effects, specifically in the bulk of the solution since the created energetic Auger electrons possess large mean free paths, and moreover, to obtain dynamical information about the ultrafast delocalization of the core-excited electron. In the considered exemplary aqueous KCl solution, the solvated isoelectronic K+ and Cl- ions exhibit notably different Auger electron spectra as a function of the photon energy. Differences appear due to dipole-forbidden transitions in aqueous K+ whose occurrence, according to the performed ab initio calculations, becomes possible only in the presence of solvent water molecules.

6.
Phys Chem Chem Phys ; 20(6): 4415-4421, 2018 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-29372210

RESUMO

Hydride molecular ions are key ingredients of the interstellar chemistry since they are precursors of more complex molecules. In regions located near a soft X-ray source these ions may resonantly absorb an X-ray photon which triggers a complex chain of reactions. In this work, we simulate ab initio the X-ray absorption spectrum, Auger decay processes and the subsequent fragmentation dynamics of two hydride molecular ions, namely CH2+ and CH3+. We show that these ions feature strong X-ray absorption resonances which relax through Auger decay within 7 fs. The doubly-charged ions thus formed mostly dissociate into smaller ionic carbon fragments: in the case of CH2+, the dominant products are either C+/H+/H or CH+/H+. For CH3+, the system breaks primary into CH2+ and H+, which provides a new route to form CH2+ near a X-ray source. Furthermore, our simulations provide the branching ratios of the final products formed after the X-ray absorption as well as their kinetic and internal energy distributions. Such data can be used in the chemistry models of the interstellar medium.

7.
Phys Rev Lett ; 119(8): 083403, 2017 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-28952742

RESUMO

Inner-valence ionized states of atoms and molecules live shorter if these species are embedded in an environment due to the possibility for ultrafast deexcitation known as interatomic Coulombic decay (ICD). In this Letter we show that the lifetime of these ICD active states decreases further when a bridge atom is in proximity to the two interacting monomers. This novel mechanism, termed superexchange ICD, is an electronic correlation effect driven by the efficient energy transfer via virtual states of the bridge atom. The superexchange ICD is discussed in detail on the example of the NeHeNe trimer. We demonstrate that the decay width of the Ne^{+}(2s^{-1}) ^{2}Σ_{g}^{+} resonance increases 6 times in the presence of the He atom at a distance of 4 Å between the two Ne atoms. Using a simple model, we provide a qualitative explanation of the superexchange ICD and we derive analytical expressions for the dependence of the decay width on the distance between the neon atoms.

8.
J Chem Phys ; 146(24): 244109, 2017 Jun 28.
Artigo em Inglês | MEDLINE | ID: mdl-28668042

RESUMO

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.

9.
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.

10.
J Phys Chem A ; 121(1): 45-50, 2017 Jan 12.
Artigo em Inglês | MEDLINE | ID: mdl-27976576

RESUMO

Benzene dimer is a prototype to study intermolecular interactions between aromatic systems. Owing to the weak interactions between the molecules within the dimer, several conformational geometries are nearly isoenergetic and thus coexist even at low temperatures. Furthermore, standard spectroscopies are unable to distinguish between them. In this work, we study the electronic relaxation processes following inner-valence ionization of benzene and the lowest conformers of benzene dimer. We show that the kinetic energy distributions of the secondary electrons emitted via two autoionization mechanisms, namely, the Auger and the intermolecular coulombic decay (ICD) effects, provide a means to probe the conformers of benzene dimer. The proposed spectroscopy opens the way to a better characterization of weakly bound molecular clusters.

11.
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.

12.
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.

13.
J Chem Phys ; 135(15): 154113, 2011 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-22029303

RESUMO

The second-order algebraic construction (ADC(2)) approach to the two-particle (pp) propagator, devised to compute double ionization energies and associated spectroscopic amplitudes, is reformulated and extended using the concept of intermediate state representations (ISR). The ISR formulation allows one to go beyond the general limitations inherent to the propagator approach, as here (N-2)-electron wave functions and properties become directly accessible. The (N-2)-electron ISR(2) equations for a general one-particle operator have been derived and implemented in a recent version of the double ionization ADC(2) program. As a first test of the method, the dipole moments of a series of 2h states of LiH, HF, and H(2)O were computed and compared to the results of a full configuration interaction (FCI) treatment. The dipole moments obtained at the ADC(2)/ISR(2) computational level are in good agreement with the FCI results.

14.
Phys Chem Chem Phys ; 11(41): 9545-55, 2009 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-19830340

RESUMO

The importance of strict adherence to proper symmetry and careful examination of various Jahn-Teller isomers was demonstrated on geometrically optimized models of Cu(acac)(2)(3NOPy)(2) and Cu(acac)(2)(4NOPy)(2) complexes. It was shown that qualitatively the results are basis-set-independent. Spin density distribution and natural orbital analysis allowed rationalization of the stable spin states of the complexes. Based on comparison between the characteristics of the free radical-ligand and the complex with Cu(acac)(2), a protocol for molecular design of Cu(II) spin-hybrid systems with desired magnetic properties is suggested.

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