Letter pubs.acs.org/JPCL
The Role of the Partner Atom and Resonant Excitation Energy in Interatomic Coulombic Decay in Rare Gas Dimers Patrick O’Keeffe,*,† Enrico Ripani,† Paola Bolognesi,† Marcello Coreno,† Michele Devetta,‡ Carlo Callegari,§,† Michele Di Fraia,∥,§ Kevin Charles Prince,§ Robert Richter,§ Michele Alagia,⊥ Antti Kivimak̈ i,⊥ and Lorenzo Avaldi† †
CNR-IMIP, Area della Ricerca di Roma 1, Monterotondo Scalo, Italy Dipartimento di Fisica, Università degli Studi di Milano, Milan, Italy § Elettra-Sincrotrone Trieste, Area Science Park, 34149 Trieste, Italy ∥ Department of Physics, University of Trieste, 34127 Trieste, Italy ⊥ CNR-IOM, Laboratorio TASC, 34149 Trieste, Italy ‡
S Supporting Information *
ABSTRACT: 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 2p−1 3/2 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. SECTION: Spectroscopy, Photochemistry, and Excited States
I
condensed matter chemistry and in living tissues, where electrons and energetic radical cations may produce irreparable damage to DNA.11 This has led, on one hand, to studies involving water dimers and clusters and solutions12−14 and, on the other hand, to pose the question on how one may control ICD. A possible route to this goal is to resonantly excite one of the components of the system which then decays to states that either can or cannot undergo ICD. This is the approach taken in this work; we choose Ar−Ar and Ar−Ne dimers because the excitation and de-excitation processes can be understood in terms of the corresponding processes in a free atom. The sharp atomic-like resonances that provide an easy handle to control the opening of ICD channels with increasing photon energy along with the existence of a well-defined initial molecular state allow a quantitative description of the process. Such an approach based on resonant Auger (RA) induced ICD has been suggested and discussed theoretically by Gokhberg et al.15 Furthermore, ICD after RA decay has been demonstrated recently by experimental works on argon dimers16 and molecular dimers,17 but control of the ICD by RA has until now not been proven. Rare gas dimers are benchmark systems for the experimental study of ICD, as they are easily produced in a cooled supersonic expansion. Furthermore, it is possible to experimentally identify
nteratomic Coulombic decay (ICD) is a process that, although only recently predicted theoretically1 and confirmed experimentally,2,3 is proving to be quite ubiquitous in van der Waals complexes, H-bonded systems, clusters, and condensed phase physics (for a full account see reviews4,5). It occurs when a system containing two or more atoms (or molecules) is perturbed by an event that leaves a singly ionized system with one of its components with an inner valence hole. If the energy of this state lies below the double ionization potential of the isolated atom (molecule), then the system cannot decay by autoionization, but only via radiative decay, which is a slow process. However, if the atom has a neighbor, the system can relax more quickly by transfer of energy from the excited ion to the neutral partner (via the Coulomb interaction) and the emission of a low energy electron from the latter. This leads to two singly ionized atoms (molecules), which then undergo a Coulomb explosion. In Ne clusters, where the ICD process was first demonstrated,2,3 ℏω
NeN(2s22p6) ⎯→ ⎯ Ne+(2s12p6)NeN − 1(2s22p6) + e−ph → Ne+(2s22p5)Ne+(2s22p5)NeN − 2(2s22p6) + e−ICD (1)
the full process occurs in 6 fs for bulk Ne+.6 Since ICD occurs each time an inner valence ionized atom (molecule) cannot autoionize7−10 and is linked via a weak interaction to one or more partners, ICD is considered to be a relevant process in © XXXX American Chemical Society
Received: March 27, 2013 Accepted: May 10, 2013
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the ICD channel by coincidence detection of all the charged particle products. The idea of the experiments performed here is to resonantly excite an inner shell electron of a rare gas atom within a dimer to an unoccupied orbital. The dimer then undergoes RA decay, and the branching ratios of the various decay channels change depending on the resonance that has been excited. We demonstrate this effect by exciting Ar2 and NeAr, via the Ar 2p−1 3/2 nl inner-shell resonances (nl = 3d, 4d and 5d; see Figure 1). The overall process we investigate is Ar···Rg + hω
1 → Ar(2p−3/2 nl)···Rg
1 Ar(2p−3/2 nl)···Rg → Ar +*···Rg + e−RA
Ar +*···Rg
→ Ar +(3p−1) + Rg + + e−ICD
(2)
Figure 2. PECs of the ArRg dimer systems used to illustrate the ICD process induced by RA. The ground state PEC of ArRg (here only Ar2 for clarity) is very weakly bound, while the ground state wave function is centered at an internuclear distance of 3.76 Å . The resonant excitation (RE) induces the transition to (for example) the Ar 2p−1 3/23d Rg state, which can decay via RA decay to the Ar+*3d-Rg state. This state can then undergo ICD, resulting in emission of an electron and Coulomb explosion of the Ar+···Ar+ state. The Ar+···Ar+ and Ar2+···Ar (Ar2+···Ne is similar on this scale) are taken from ref 18, while the Ne+···Ar+ is a e2/r curve shifted to the Ne+ + Ar+ asymptotic limit.
Ar(2p−13d)Ar → Ar+(3p4 (1D)3d (2D))Ar + e−RA → Ar+ + Ar+ + e−ICD process. While all Ar+*nd-Ar states lie above the Ar+···Ar+ curve at the ground state equilibrium distance (shaded area in Figure 2) and thus can undergo ICD, some of the Ar+*nd-Ne states lie below the Ar+···Ne+ curve. It should be noted, however, that the RA process also includes shakeup processes in which, for example, Ar+*(n+1)d-Rg and Ar+*(n +2)d-Rg states can be formed following excitation of an Ar 2p−1 3/2nd resonance. This could be a possible explanation for the −1 anomalous intensity distribution of the Ar 2p−1 3/23d, Ar 2p3/24d, + + − −1 and Ar 2p3/25d resonances in the Ar /Ne /e spectrum, where it could be suggested that only a few shakeup states can undergo ICD following decay from the Ar 2p−1 3/23d resonance, while for the Ar 2p−1 4d resonance most shakeup states can give 3/2 a low energy electron through ICD, and, finally, for the 5d state both spectator and shakeup processes give rise to states that can undergo ICD. The above is true in the atomic model, where it is assumed that the dimer has the same absorption cross section as the atom. This is not necessarily a good approximation, and we need to consider molecular effects. Indeed, for the e−/Ar+/Ar+ spectrum (Figure 1b), the resonances shift to lower energy and broaden (while for NeAr they remain at similar energies). This can be understood by considering the core-hole and the ground state PECs of the dimers. The ground state PECs of the Ar2 and NeAr dimers are very weakly bound with ground state well depths of 12.3 and 5.7 meV, respectively.19 We have not found core-hole PECs of these dimers in the literature; however, we invoke the equivalent-core approximation20 and replace them
Figure 1. A scan of the synchrotron energy in the region of the Ar −1 −1 2p−1 3/23d, Ar 2p3/24d, and Ar 2p3/25d resonances showing the yield of − + − + + (a) e /Ar , (b) e /Ar /Ar , and (c) e−/Ar+/Ne+ coincidences as a function of the photon energy (see Experimental Methods for details).
where Rg = Ar or Ne, and Ar+* represents any one of the many possible final state of the RA decay step. In the cooled supersonic expansion used, dimers are only 99% unperturbed atoms, and therefore process 2 is rare compared to the RA of free atoms (Ar + hω→ Ar(2p−1nl) → Ar+ + e−). The latter is detected as a double coincidence (e−/Ar+) and serves as a reference (Figure 1a), whereas the triple coincidence detection (e−/Ar+/Rg+) sifts out process 2 (note the different signal-to-noise ratio in Figure 1a with respect to Figure 1b,c). Furthermore, the coexpansion of Ar and Ne allows both Ar2 and NeAr dimers to be formed in the same beam, while the coincidences allow us to select out events related to each dimer. The idea of using RA to control ICD can be understood more clearly by examining the potential energy curves (PECs) in Figure 2. Let us examine the simpler case of spectator Auger decay, where the resonantly excited electron does not participate in the decay process: the choice of the resonance being excited determines which Ar+*nd-Rg state is accessed. The particular case illustrated in Figure 2 is the Ar2 + hω→ 1798
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with the corresponding PECs of K−Ar;21 for Ar−Ne not even the substitute K−Ne PECs exist, but based on the argument that the attractive forces scale with the polarizabilities of the Rg partner (Ar: 11.07 au; Ne: 2.67 au), the shift will be a factor of 4 smaller, which is not significantly compensated by a shorter equilibrium distance in the ground state (Ar2: 3.76 Å; NeAr: 3.46 Å).19 These curves show that the lowest core-hole state is more bound than the ground state of the dimer, therefore resulting in a negative shift of the resonances, while for NeAr the 4 times smaller shift is not detectable on the scale of the experiment. Finally, the broadening of the peaks may be due to excitation to electronic excited states of the Ar(2p−1 3/2nl)Rg manifold. In order to corroborate the model outlined above, we have performed a second experiment in which the kinetic energy (KE) distribution of the low energy electrons produced in coincidence with Ar+/Ar+ and Ar+/Ne+ ions were measured in an electron imaging experiment (see Experimental Methods for technical details). The resulting electron KE distributions for the three resonances examined are shown in Figure 3a,c,e. The
that the intensity distribution is governed by the probability that the corresponding state is populated by RA. The experimental RA spectra of atomic Ar22−24 were therefore used as input data for this model. By subtracting the energy of the Auger electron, the sum of the ionization energy of the two ions and the quantity of energy channeled into the KE of the ions due to Coulomb explosion at the equilibrium internuclear distance of the ground state (4 eV) from the photon energy, one obtains the energy of the ICD electron (stick spectra in Figure 3b,d,f). Furthermore, if we can assume that the RA + ICD process is so rapid that we can neglect the motion of the nuclei, a convolution over the probability distribution for the initial-state internuclear distance P(r) (which we take to be the square of the wave function of the lowest vibrational state of the dimer) is sufficient. We therefore convolute the stick spectrum with P(r), with P(r) dr taken as an implicit function of E. While this can be done exactly, it is more instructive to note that P(E) dE is well approximated by the projection of P(r) onto the Ar+−Ar+ PEC, so that the final spectrum is well approximated by a Gaussian broadening of 500 meV (full width halfmaximum). Both the stick spectra and convoluted distributions −1 are plotted in Figure 3b,d,f for the Ar 2p−1 3/23d, Ar 2p3/24d, and −1 Ar 2p3/25d resonances. Also shown is the energetic limit above which the autoionization of Ar+*nd-Rg to Ar2+-Rg states competes with ICD. This simple model does not provide a quantitative description of the process, but, remarkably, it does capture the essence of the problem: in Figure 3, one can see that the general trends of the experimental data are reproduced and, in the case of the Ar 2p−1 3/23d resonance, even the substructure. At first sight it would seem that the model breaks down significantly for the Ar 2p−1 3/25d resonance where the peaks at 0.5 and 2.5 eV do not have any correspondence in the simple empirical model. A possible explanation for this can be obtained by examining the KE distribution of the low-energy electrons formed in coincidence with the Ar2+ ion, which arise mainly from the monomer in the beam (red lines in Figure 3a,c,e). The peaks in the e−/Ar2+ spectrum correspond to the “unexpected” peaks in the dimer coincidence spectrum. Thus we postulate that the decay processes giving rise to these electrons are similar, i.e., decay of the Ar+* and Ar+*nd-Ar states to Ar2+ and Ar2+−Ar, respectively. The Ar2+−Ar state produced in the case of the dimer then transfers to the Ar+···Ar+ curve leading to a Coulomb explosion and thus a low energy electron/Ar+/Ar+ coincidence. Furthermore, the peaks in the ICD model lying above the Ar2+ limit find no corresponding structures in the experimental spectrum (i.e., those with KE > 8 eV). The equivalent results based on the e−/Ne+/Ar+ coincidences originating from the NeAr dimers are presented in Figure 4. The experimental data shows that the ICD electrons have spectra peaked at 0 eV. From the empirical model point of view, the most significant difference is that for this system the Ar+··· Ne+ asymptote lies 5.81 eV above that of the Ar+···Ar+ asymptote (see Figure 2). This simply means that the simulated electron KE is shifted to lower energies by this amount (compare the right-hand sides of Figures 3 and 4) and thus that the simulated electron KE distributions are peaked at zero, in agreement with the experiment. Comparing the right-hand sides of Figures 3 and 4 again, one notes that the number of states open to ICD increases on going from resonant excitation to the 3d → 4d → 5d resonances for NeAr (as described above when discussing the intensities of Figure 1c). The result is that the e−/Ne+/Ar+ spectrum in
Figure 3. Left panel: black (red) traces are the electron kinetic energy (KE) distributions obtained for e−/Ar+/Ar+ (e−/Ar2+) coincidences for the various resonances indicated and normalized to each other for KEs >12 eV. Right panels are ICD electron KE distributions estimated from experimental RA spectra of the atom (see text for details). The vertical dashed line is the threshold above which autoionization to Ar2+Ar after RA is energetically open.
angular distributions were isotropic as expected for the ICD process and are therefore not reported. In Figure 3, the KE distribution of the ejected electrons increases from the Ar −1 2p−1 3/23d to the Ar 2p3/24d resonance and then slightly increases on passing to the Ar 2p−1 3/25d resonance. To rationalize these observations, an empirical model can be used to estimate the distribution of the ICD electron KEs. This model works on the assumption that the Ar+*Ar states undergoing ICD can be well approximated from an energetic point of view by the corresponding atomic states Ar+* and, therefore, that the energy difference between these states and the Ar+··· Ar+ asymptotic limit is the total energy available to each state after it undergoes ICD. Also, it is assumed that all states energetically open to ICD actually undergo ICD and therefore 1799
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plate detector, while the ions produced are sent in the opposite direction into a 10.5 cm time-of-flight (TOF) tube. The numbers of e−/Ar+, e−/Ar+/Ar+, and e−/Ne+/Ar+ coincidence per photon energy are extracted from a single scan, and the results are shown in Figure 1. The second experiment used an electron velocity map imaging (VMI) apparatus based on a delay line position sensitive detector (PSD) together with an ion TOF similar to that described above26 (for a schematic outline and further technical details of this experimental apparatus, see Supporting Information Figure S2). In this setup, the same experiment as above is performed, but with the significant advantage that it is now possible to extract the energy and angular distributions of the electrons in coincidence with any selected region of the ion−ion TOF map described above. The VMI technique is based on the projection of the expanding sphere of electrons onto a two-dimensional PSD. In order to retrieve the angular distribution and angle integrated photoelectron spectrum from this image, it is necessary to apply an inversion technique based on the Abel inversion, which takes advantage of the cylindrical symmetry of the original three-dimensional (3D) system to extract from the projection image a slice through the original 3D distribution. Data was acquired at the photon energies −1 corresponding to the maxima of the Ar 2p−1 3/23d, Ar 2p3/24d, and −1 Ar 2p3/25d resonances for the dimers as determined in the first experiment, and the VMI images in coincidence with the two Ar+ generated in the Coulomb explosion were extracted. These images were inverted using the pBasex method,27 and the resulting KE distributions for the Ar2 and NeAr dimers are shown in Figures 3 and 4, respectively.
Figure 4. Left panel: the electron KE distributions obtained selecting e−/Ne+/Ar+ coincidences for the resonances indicated. Right panels are the ICD electron KE distributions estimated from experimental RA spectra of argon atoms (see text and Figure 3). The vertical dashed line is the energy above which the states produced by RA can undergo autoionization to Ar2+Ne.
Figure 1c presents a different intensity distribution with respect to the e−/Ar+/Ar+ spectrum in Figures 1b, where all states formed by RA are open to ICD. Considering that the apparatus used in the first experiment, while favoring low energy electrons, also detects RA electrons with an efficiency of ≈50%, the fact that the opening of the ICD channel so significantly changes the relative intensities in Figure 1c indicates that ICD is a major decay channel after RA; otherwise, the relative intensities in Figure 1c would not change (if we assume that molecular effects on the cross section are small). In conclusion, it has been demonstrated that the ICD process takes place after RA decay in the Ar2 and NeAr rare gas dimers and represents a major channel in the cascade following core excitation. More importantly, it has been shown that it is possible to tune the ICD electron KE simply by choosing the resonance at which the dimer is photoexcited or, indeed, that it is possible to gradually switch on or off the ICD channel by exciting the appropriate resonance with the more suitable partner atom (Ne or Ar). Therefore, the resonance Auger-ICD cascade exploits the site and energy selectivity of core excitation to locate the energy deposition in the system. Note added: The control of ICD using RA decay in the ArKr and ArXe dimers has been very recently independently observed.25
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ASSOCIATED CONTENT
S Supporting Information *
Schematic layouts of the two experimental set-ups used are given and described in the Supporting Information. This material is available free of charge via the Internet at http:// pubs.acs.org/.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: patrick.okeeff[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank K. Gokhberg, A. Kuleff, and L. S. Cederbaum for stimulating discussions. We also thank L. Stebel, R. Sergo, and G. Cautero for help in setting up the position sensitive detector. This work was partially supported by the MIUR PRIN 2009W2W4YF and 2009SLKFEX.
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EXPERIMENTAL METHODS Two separate experiments have been performed: the first experiment is an electron−ion−ion coincidence experiment (see Supporting Information Figure S1 for a schematic layout and technical details). In the interaction region of this apparatus, synchrotron light from the Gas phase beamline of the Italian synchrotron source, Elettra, crosses a liquid nitrogen cooled supersonic beam made by expansion of a mixture of Ar and Ne through a 50 μm orifice. The electrons produced in this way are accelerated by an extraction field to a microchannel
REFERENCES
(1) Cederbaum, L. S.; Zobeley, J.; Tarantelli, F. Giant Intermolecular Decay and Fragmentation of Clusters. Phys. Rev. Lett. 1997, 79, 4778− 4781. (2) Marburger, S.; Kugeler, O.; Hergenhahn, U.; Mö ller, T. Experimental Evidence for Interatomic Coulombic Decay in Ne Clusters. Phys. Rev. Lett. 2003, 90, 203401. (3) Jahnke, T.; Czasch, A.; Schöffler, M. S.; Schössler, S.; Knapp, A.; Käsz, M.; Titze, J.; Wimmer, C.; Kreidi, K.; Grisenti, R. E.; Staudte, A.; Jagutzki, O.; Hergenhahn, U.; Schmidt-Böcking, H.; Dörner, R. Experimental Observation of Interatomic Coulombic Decay in Neon Dimers. Phys. Rev. Lett. 2004, 93, 163401.
1800
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The Journal of Physical Chemistry Letters
Letter
(4) Hergenhahn, U. Interatomic and Intermolecular Coulombic Decay: The Early Years. J. Electr. Spectr. Relat. Phenom. 2011, 184, 78− 90. (5) Averbukh, V.; Demekhin, P.; Kolorenc, P.; Scheit, S.; Stoychev, S.; Kuleff, A.; Chiang, Y.-C.; Gokhberg, K.; Kopelke, S.; Sisourat, N.; Cederbaum, L. Interatomic Electronic Decay Processes in Singly and Multiply Ionized Clusters. J. Electron Spectrosc. Relat. Phenom. 2011, 183, 36−47. (6) Ö hrwall, G.; Tchaplyguine, M.; Lundwall, M.; Feifel, R.; Bergersen, H.; Rander, T.; Lindblad, A.; Schulz, J.; Peredkov, S.; Barth, S.; Marburger, S.; Hergenhahn, U.; Svensson, S.; Björneholm, O. Femtosecond Interatomic Coulombic Decay in Free Neon Clusters: Large Lifetime Differences between Surface and Bulk. Phys. Rev. Lett. 2004, 93, 173401. (7) Lablanquie, P.; Aoto, T.; Hikosaka, Y.; Morioka, Y.; Penent, F.; Ito, K. Appearance of Interatomic Coulombic Decay in Ar, Kr, and Xe Homonuclear Dimers. J. Chem. Phys. 2007, 127, 154323. (8) Morishita, Y.; Liu, X.-J.; Saito, N.; Lischke, T.; Kato, M.; Prümper, G.; Oura, M.; Yamaoka, H.; Tamenori, Y.; Suzuki, I. H.; et al. Experimental Evidence of Interatomic Coulombic Decay from the Auger Final States in Argon Dimers. Phys. Rev. Lett. 2006, 96, 243402. (9) Barth, S.; Joshi, S.; Marburger, S.; Ulrich, V.; Lindblad, A.; Ö hrwall, G.; Björneholm, O.; Hergenhahn, U. Observation of Resonant Interatomic Coulombic Decay in Ne Clusters. J. Chem. Phys. 2005, 122, 241102. (10) Aoto, T.; Ito, K.; Hikosaka, Y.; Shigemasa, E.; Penent, F.; Lablanquie, P. Properties of Resonant Interatomic Coulombic Decay in Ne Dimers. Phys. Rev. Lett. 2006, 97, 243401. (11) Grieves, G. A.; Orlando, T. M. Intermolecular Coulomb Decay at Weakly Coupled Heterogeneous Interfaces. Phys. Rev. Lett. 2011, 107, 016104. (12) Jahnke, T.; Sann, H.; Havermeier, T.; Kreidi, K.; Stuck, C.; Meckel, M.; Schoeffler, M.; Neumann, N.; Wallauer, R.; Voss, S.; et al. Ultrafast Energy Transfer between Water Molecules. Nat. Phys. 2010, 6, 139−142. (13) Mucke, M.; Braune, M.; Barth, S.; Förstel, M.; Lischke, T.; Ulrich, V.; Arion, T.; Becker, U.; Bradshaw, A.; Hergenhahn, U. A Hitherto Unrecognized Source of Low-Energy Electrons in Water. Nat. Phys. 2010, 6, 143−146. (14) Aziz, E. F.; Ottosson, N.; Faubel, M.; Hertel, I. V.; Winter, B. Interaction between Liquid Water and Hydroxide Revealed by Core− Hole De-excitation. Nature 2008, 455, 89−91. (15) Gokhberg, K.; Kolorenc, P.; Kuleff, A. I.; Cederbaum, L. S. A New Intermolecular Mechanism to Selectively Drive Photoinduced Damages. arXiv.org, e-Print Arch., Phys. (physics.atm-clus) 2013, No. arXiv:1303.6440. (16) Kimura, M.; Fukuzawa, H.; Sakai, K.; Mondal, S.; Kukk, E.; Kono, Y.; Nagaoka, S.; Tamenori, Y.; Saito, N.; Ueda, K. Efficient SiteSpecific Low-Energy Electron Production via Interatomic Coulombic Decay Following Resonant Auger Decay. Phys. Rev. A 2013, 87, 043414. (17) Trinter, F.; Schoffler, M. S.; Kim, H.-K.; Sturm, F.; Cole, K.; Neumann, N.; Vredenborg, A.; Williams, J.; Bocharova, I.; Guillemin, R. Experimental Proof of Resonant Auger Decay Driven Intermolecular Coulombic Decay. Nature 2013, submitted for publication. (18) Saito, N.; Morishita, Y.; Suzuki, I.; Stoychev, S.; Kuleff, A.; Cederbaum, L.; Liu, X.-J.; Fukuzawa, H.; Prumper, G.; Ueda, K. Evidence of Radiative Charge Transfer in Argon Dimers. Chem. Phys. Lett. 2007, 441, 16−19. (19) Cybulski, S. M.; Toczylowski, R. R. Ground State Potential Energy Curves for He2, Ne2, Ar2, He−Ne, He−Ar, and Ne−Ar: A Coupled-Cluster Study. J. Chem. Phys. 1999, 111, 10520−10528. (20) Jolly, W. L.; Hendrickson, D. N. Thermodynamic Interpretation of Chemical Shifts in Core Electron Binding Energies. J. Am. Chem. Soc. 1970, 92, 1863−1871. (21) El-Hadj-Rhouma, M. B.; Berriche, H.; Lakhdar, Z. B.; Spiegelman, F. One-Electron Pseudopotential Calculations of Excited States of LiAr, NaAr, and KAr. J. Chem. Phys. 2002, 116, 1839−1849.
(22) Meyer, M.; v. Raven, E.; Sonntag, B.; Hansen, J. E. Decay of the Ar 2p5 nd Core Resonances: An Autoionization Spectrum Dominated by Shake Processes. Phys. Rev. A 1991, 43, 177−188. (23) de Gouw, J. A.; van Eck, J.; Peters, A. C.; van der Weg, J.; Heideman, H. G. M. Resonant Auger Spectra of the 2p−1 nl States of Argon. J. Phys. B 1995, 28, 2127−2141. (24) Mursu, J.; Aksela, H.; Sairanen, O.-P.; Kivimäki, A.; Nõmmiste, E.; Ausmees, A.; Svensson, S.; Aksela, S. Decay of the 2p54s, 2p53d and 2p54d States of Ar Studied by Utilizing the Auger Resonant Raman Effect. J. Phys. B 1996, 29, 4387−4399. (25) Kimura, M.; Fukuzawa, H.; Tachibana, T.; Yuta Ito, S. M.; Schoffler, M.; Williams, J.; Yuhai Jiang, Y. T.; Saito, N.; Ueda, K. Controlling Low-energy Electron Emission via Resonant-Augerinduced Interatomic Coulombic Decay. J. Phys. Chem. Lett. 2013, DOI: 10.1021/jz4006674. (26) O’Keeffe, P.; Bolognesi, P.; Coreno, M.; Moise, A.; Richter, R.; Cautero, G.; Stebel, L.; Sergo, R.; Pravica, L.; Ovcharenko, Y.; et al. A Photoelectron Velocity Map Imaging Spectrometer for Experiments Combining Synchrotron and Laser Radiations. L. Rev. Sci. Instrum. 2011, 82, 033109. (27) Garcia, G. A.; Nahon, L.; Powis, I. Two-Dimensional Charged Particle Image Inversion using a Polar Basis Function Expansion. Rev. Sci. Instrum. 2004, 75, 4989−4996.
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The Role of the Partner Atom and Resonant Excitation Energy in Interatomic Coulombic Decay in Rare Gas Dimers Patrick O’Keeffe,*,† Enrico Ripani,† Paola Bolognesi,† Marcello Coreno,† Michele Devetta,‡ Carlo Callegari,§,† Michele Di Fraia,∥,§ Kevin Charles Prince,§ Robert Richter,§ Michele Alagia,⊥ Antti Kivimak̈ i,⊥ and Lorenzo Avaldi† †
CNR-IMIP, Area della Ricerca di Roma 1, Monterotondo Scalo, Italy Dipartimento di Fisica, Università degli Studi di Milano, Milan, Italy § Elettra-Sincrotrone Trieste, Area Science Park, 34149 Trieste, Italy ∥ Department of Physics, University of Trieste, 34127 Trieste, Italy ⊥ CNR-IOM, Laboratorio TASC, 34149 Trieste, Italy ‡
S Supporting Information *
ABSTRACT: 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 2p−1 3/2 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. SECTION: Spectroscopy, Photochemistry, and Excited States
I
condensed matter chemistry and in living tissues, where electrons and energetic radical cations may produce irreparable damage to DNA.11 This has led, on one hand, to studies involving water dimers and clusters and solutions12−14 and, on the other hand, to pose the question on how one may control ICD. A possible route to this goal is to resonantly excite one of the components of the system which then decays to states that either can or cannot undergo ICD. This is the approach taken in this work; we choose Ar−Ar and Ar−Ne dimers because the excitation and de-excitation processes can be understood in terms of the corresponding processes in a free atom. The sharp atomic-like resonances that provide an easy handle to control the opening of ICD channels with increasing photon energy along with the existence of a well-defined initial molecular state allow a quantitative description of the process. Such an approach based on resonant Auger (RA) induced ICD has been suggested and discussed theoretically by Gokhberg et al.15 Furthermore, ICD after RA decay has been demonstrated recently by experimental works on argon dimers16 and molecular dimers,17 but control of the ICD by RA has until now not been proven. Rare gas dimers are benchmark systems for the experimental study of ICD, as they are easily produced in a cooled supersonic expansion. Furthermore, it is possible to experimentally identify
nteratomic Coulombic decay (ICD) is a process that, although only recently predicted theoretically1 and confirmed experimentally,2,3 is proving to be quite ubiquitous in van der Waals complexes, H-bonded systems, clusters, and condensed phase physics (for a full account see reviews4,5). It occurs when a system containing two or more atoms (or molecules) is perturbed by an event that leaves a singly ionized system with one of its components with an inner valence hole. If the energy of this state lies below the double ionization potential of the isolated atom (molecule), then the system cannot decay by autoionization, but only via radiative decay, which is a slow process. However, if the atom has a neighbor, the system can relax more quickly by transfer of energy from the excited ion to the neutral partner (via the Coulomb interaction) and the emission of a low energy electron from the latter. This leads to two singly ionized atoms (molecules), which then undergo a Coulomb explosion. In Ne clusters, where the ICD process was first demonstrated,2,3 ℏω
NeN(2s22p6) ⎯→ ⎯ Ne+(2s12p6)NeN − 1(2s22p6) + e−ph → Ne+(2s22p5)Ne+(2s22p5)NeN − 2(2s22p6) + e−ICD (1)
the full process occurs in 6 fs for bulk Ne+.6 Since ICD occurs each time an inner valence ionized atom (molecule) cannot autoionize7−10 and is linked via a weak interaction to one or more partners, ICD is considered to be a relevant process in © XXXX American Chemical Society
Received: March 27, 2013 Accepted: May 10, 2013
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the ICD channel by coincidence detection of all the charged particle products. The idea of the experiments performed here is to resonantly excite an inner shell electron of a rare gas atom within a dimer to an unoccupied orbital. The dimer then undergoes RA decay, and the branching ratios of the various decay channels change depending on the resonance that has been excited. We demonstrate this effect by exciting Ar2 and NeAr, via the Ar 2p−1 3/2 nl inner-shell resonances (nl = 3d, 4d and 5d; see Figure 1). The overall process we investigate is Ar···Rg + hω
1 → Ar(2p−3/2 nl)···Rg
1 Ar(2p−3/2 nl)···Rg → Ar +*···Rg + e−RA
Ar +*···Rg
→ Ar +(3p−1) + Rg + + e−ICD
(2)
Figure 2. PECs of the ArRg dimer systems used to illustrate the ICD process induced by RA. The ground state PEC of ArRg (here only Ar2 for clarity) is very weakly bound, while the ground state wave function is centered at an internuclear distance of 3.76 Å . The resonant excitation (RE) induces the transition to (for example) the Ar 2p−1 3/23d Rg state, which can decay via RA decay to the Ar+*3d-Rg state. This state can then undergo ICD, resulting in emission of an electron and Coulomb explosion of the Ar+···Ar+ state. The Ar+···Ar+ and Ar2+···Ar (Ar2+···Ne is similar on this scale) are taken from ref 18, while the Ne+···Ar+ is a e2/r curve shifted to the Ne+ + Ar+ asymptotic limit.
Ar(2p−13d)Ar → Ar+(3p4 (1D)3d (2D))Ar + e−RA → Ar+ + Ar+ + e−ICD process. While all Ar+*nd-Ar states lie above the Ar+···Ar+ curve at the ground state equilibrium distance (shaded area in Figure 2) and thus can undergo ICD, some of the Ar+*nd-Ne states lie below the Ar+···Ne+ curve. It should be noted, however, that the RA process also includes shakeup processes in which, for example, Ar+*(n+1)d-Rg and Ar+*(n +2)d-Rg states can be formed following excitation of an Ar 2p−1 3/2nd resonance. This could be a possible explanation for the −1 anomalous intensity distribution of the Ar 2p−1 3/23d, Ar 2p3/24d, + + − −1 and Ar 2p3/25d resonances in the Ar /Ne /e spectrum, where it could be suggested that only a few shakeup states can undergo ICD following decay from the Ar 2p−1 3/23d resonance, while for the Ar 2p−1 4d resonance most shakeup states can give 3/2 a low energy electron through ICD, and, finally, for the 5d state both spectator and shakeup processes give rise to states that can undergo ICD. The above is true in the atomic model, where it is assumed that the dimer has the same absorption cross section as the atom. This is not necessarily a good approximation, and we need to consider molecular effects. Indeed, for the e−/Ar+/Ar+ spectrum (Figure 1b), the resonances shift to lower energy and broaden (while for NeAr they remain at similar energies). This can be understood by considering the core-hole and the ground state PECs of the dimers. The ground state PECs of the Ar2 and NeAr dimers are very weakly bound with ground state well depths of 12.3 and 5.7 meV, respectively.19 We have not found core-hole PECs of these dimers in the literature; however, we invoke the equivalent-core approximation20 and replace them
Figure 1. A scan of the synchrotron energy in the region of the Ar −1 −1 2p−1 3/23d, Ar 2p3/24d, and Ar 2p3/25d resonances showing the yield of − + − + + (a) e /Ar , (b) e /Ar /Ar , and (c) e−/Ar+/Ne+ coincidences as a function of the photon energy (see Experimental Methods for details).
where Rg = Ar or Ne, and Ar+* represents any one of the many possible final state of the RA decay step. In the cooled supersonic expansion used, dimers are only 99% unperturbed atoms, and therefore process 2 is rare compared to the RA of free atoms (Ar + hω→ Ar(2p−1nl) → Ar+ + e−). The latter is detected as a double coincidence (e−/Ar+) and serves as a reference (Figure 1a), whereas the triple coincidence detection (e−/Ar+/Rg+) sifts out process 2 (note the different signal-to-noise ratio in Figure 1a with respect to Figure 1b,c). Furthermore, the coexpansion of Ar and Ne allows both Ar2 and NeAr dimers to be formed in the same beam, while the coincidences allow us to select out events related to each dimer. The idea of using RA to control ICD can be understood more clearly by examining the potential energy curves (PECs) in Figure 2. Let us examine the simpler case of spectator Auger decay, where the resonantly excited electron does not participate in the decay process: the choice of the resonance being excited determines which Ar+*nd-Rg state is accessed. The particular case illustrated in Figure 2 is the Ar2 + hω→ 1798
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with the corresponding PECs of K−Ar;21 for Ar−Ne not even the substitute K−Ne PECs exist, but based on the argument that the attractive forces scale with the polarizabilities of the Rg partner (Ar: 11.07 au; Ne: 2.67 au), the shift will be a factor of 4 smaller, which is not significantly compensated by a shorter equilibrium distance in the ground state (Ar2: 3.76 Å; NeAr: 3.46 Å).19 These curves show that the lowest core-hole state is more bound than the ground state of the dimer, therefore resulting in a negative shift of the resonances, while for NeAr the 4 times smaller shift is not detectable on the scale of the experiment. Finally, the broadening of the peaks may be due to excitation to electronic excited states of the Ar(2p−1 3/2nl)Rg manifold. In order to corroborate the model outlined above, we have performed a second experiment in which the kinetic energy (KE) distribution of the low energy electrons produced in coincidence with Ar+/Ar+ and Ar+/Ne+ ions were measured in an electron imaging experiment (see Experimental Methods for technical details). The resulting electron KE distributions for the three resonances examined are shown in Figure 3a,c,e. The
that the intensity distribution is governed by the probability that the corresponding state is populated by RA. The experimental RA spectra of atomic Ar22−24 were therefore used as input data for this model. By subtracting the energy of the Auger electron, the sum of the ionization energy of the two ions and the quantity of energy channeled into the KE of the ions due to Coulomb explosion at the equilibrium internuclear distance of the ground state (4 eV) from the photon energy, one obtains the energy of the ICD electron (stick spectra in Figure 3b,d,f). Furthermore, if we can assume that the RA + ICD process is so rapid that we can neglect the motion of the nuclei, a convolution over the probability distribution for the initial-state internuclear distance P(r) (which we take to be the square of the wave function of the lowest vibrational state of the dimer) is sufficient. We therefore convolute the stick spectrum with P(r), with P(r) dr taken as an implicit function of E. While this can be done exactly, it is more instructive to note that P(E) dE is well approximated by the projection of P(r) onto the Ar+−Ar+ PEC, so that the final spectrum is well approximated by a Gaussian broadening of 500 meV (full width halfmaximum). Both the stick spectra and convoluted distributions −1 are plotted in Figure 3b,d,f for the Ar 2p−1 3/23d, Ar 2p3/24d, and −1 Ar 2p3/25d resonances. Also shown is the energetic limit above which the autoionization of Ar+*nd-Rg to Ar2+-Rg states competes with ICD. This simple model does not provide a quantitative description of the process, but, remarkably, it does capture the essence of the problem: in Figure 3, one can see that the general trends of the experimental data are reproduced and, in the case of the Ar 2p−1 3/23d resonance, even the substructure. At first sight it would seem that the model breaks down significantly for the Ar 2p−1 3/25d resonance where the peaks at 0.5 and 2.5 eV do not have any correspondence in the simple empirical model. A possible explanation for this can be obtained by examining the KE distribution of the low-energy electrons formed in coincidence with the Ar2+ ion, which arise mainly from the monomer in the beam (red lines in Figure 3a,c,e). The peaks in the e−/Ar2+ spectrum correspond to the “unexpected” peaks in the dimer coincidence spectrum. Thus we postulate that the decay processes giving rise to these electrons are similar, i.e., decay of the Ar+* and Ar+*nd-Ar states to Ar2+ and Ar2+−Ar, respectively. The Ar2+−Ar state produced in the case of the dimer then transfers to the Ar+···Ar+ curve leading to a Coulomb explosion and thus a low energy electron/Ar+/Ar+ coincidence. Furthermore, the peaks in the ICD model lying above the Ar2+ limit find no corresponding structures in the experimental spectrum (i.e., those with KE > 8 eV). The equivalent results based on the e−/Ne+/Ar+ coincidences originating from the NeAr dimers are presented in Figure 4. The experimental data shows that the ICD electrons have spectra peaked at 0 eV. From the empirical model point of view, the most significant difference is that for this system the Ar+··· Ne+ asymptote lies 5.81 eV above that of the Ar+···Ar+ asymptote (see Figure 2). This simply means that the simulated electron KE is shifted to lower energies by this amount (compare the right-hand sides of Figures 3 and 4) and thus that the simulated electron KE distributions are peaked at zero, in agreement with the experiment. Comparing the right-hand sides of Figures 3 and 4 again, one notes that the number of states open to ICD increases on going from resonant excitation to the 3d → 4d → 5d resonances for NeAr (as described above when discussing the intensities of Figure 1c). The result is that the e−/Ne+/Ar+ spectrum in
Figure 3. Left panel: black (red) traces are the electron kinetic energy (KE) distributions obtained for e−/Ar+/Ar+ (e−/Ar2+) coincidences for the various resonances indicated and normalized to each other for KEs >12 eV. Right panels are ICD electron KE distributions estimated from experimental RA spectra of the atom (see text for details). The vertical dashed line is the threshold above which autoionization to Ar2+Ar after RA is energetically open.
angular distributions were isotropic as expected for the ICD process and are therefore not reported. In Figure 3, the KE distribution of the ejected electrons increases from the Ar −1 2p−1 3/23d to the Ar 2p3/24d resonance and then slightly increases on passing to the Ar 2p−1 3/25d resonance. To rationalize these observations, an empirical model can be used to estimate the distribution of the ICD electron KEs. This model works on the assumption that the Ar+*Ar states undergoing ICD can be well approximated from an energetic point of view by the corresponding atomic states Ar+* and, therefore, that the energy difference between these states and the Ar+··· Ar+ asymptotic limit is the total energy available to each state after it undergoes ICD. Also, it is assumed that all states energetically open to ICD actually undergo ICD and therefore 1799
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plate detector, while the ions produced are sent in the opposite direction into a 10.5 cm time-of-flight (TOF) tube. The numbers of e−/Ar+, e−/Ar+/Ar+, and e−/Ne+/Ar+ coincidence per photon energy are extracted from a single scan, and the results are shown in Figure 1. The second experiment used an electron velocity map imaging (VMI) apparatus based on a delay line position sensitive detector (PSD) together with an ion TOF similar to that described above26 (for a schematic outline and further technical details of this experimental apparatus, see Supporting Information Figure S2). In this setup, the same experiment as above is performed, but with the significant advantage that it is now possible to extract the energy and angular distributions of the electrons in coincidence with any selected region of the ion−ion TOF map described above. The VMI technique is based on the projection of the expanding sphere of electrons onto a two-dimensional PSD. In order to retrieve the angular distribution and angle integrated photoelectron spectrum from this image, it is necessary to apply an inversion technique based on the Abel inversion, which takes advantage of the cylindrical symmetry of the original three-dimensional (3D) system to extract from the projection image a slice through the original 3D distribution. Data was acquired at the photon energies −1 corresponding to the maxima of the Ar 2p−1 3/23d, Ar 2p3/24d, and −1 Ar 2p3/25d resonances for the dimers as determined in the first experiment, and the VMI images in coincidence with the two Ar+ generated in the Coulomb explosion were extracted. These images were inverted using the pBasex method,27 and the resulting KE distributions for the Ar2 and NeAr dimers are shown in Figures 3 and 4, respectively.
Figure 4. Left panel: the electron KE distributions obtained selecting e−/Ne+/Ar+ coincidences for the resonances indicated. Right panels are the ICD electron KE distributions estimated from experimental RA spectra of argon atoms (see text and Figure 3). The vertical dashed line is the energy above which the states produced by RA can undergo autoionization to Ar2+Ne.
Figure 1c presents a different intensity distribution with respect to the e−/Ar+/Ar+ spectrum in Figures 1b, where all states formed by RA are open to ICD. Considering that the apparatus used in the first experiment, while favoring low energy electrons, also detects RA electrons with an efficiency of ≈50%, the fact that the opening of the ICD channel so significantly changes the relative intensities in Figure 1c indicates that ICD is a major decay channel after RA; otherwise, the relative intensities in Figure 1c would not change (if we assume that molecular effects on the cross section are small). In conclusion, it has been demonstrated that the ICD process takes place after RA decay in the Ar2 and NeAr rare gas dimers and represents a major channel in the cascade following core excitation. More importantly, it has been shown that it is possible to tune the ICD electron KE simply by choosing the resonance at which the dimer is photoexcited or, indeed, that it is possible to gradually switch on or off the ICD channel by exciting the appropriate resonance with the more suitable partner atom (Ne or Ar). Therefore, the resonance Auger-ICD cascade exploits the site and energy selectivity of core excitation to locate the energy deposition in the system. Note added: The control of ICD using RA decay in the ArKr and ArXe dimers has been very recently independently observed.25
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ASSOCIATED CONTENT
S Supporting Information *
Schematic layouts of the two experimental set-ups used are given and described in the Supporting Information. This material is available free of charge via the Internet at http:// pubs.acs.org/.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: patrick.okeeff[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS The authors thank K. Gokhberg, A. Kuleff, and L. S. Cederbaum for stimulating discussions. We also thank L. Stebel, R. Sergo, and G. Cautero for help in setting up the position sensitive detector. This work was partially supported by the MIUR PRIN 2009W2W4YF and 2009SLKFEX.
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EXPERIMENTAL METHODS Two separate experiments have been performed: the first experiment is an electron−ion−ion coincidence experiment (see Supporting Information Figure S1 for a schematic layout and technical details). In the interaction region of this apparatus, synchrotron light from the Gas phase beamline of the Italian synchrotron source, Elettra, crosses a liquid nitrogen cooled supersonic beam made by expansion of a mixture of Ar and Ne through a 50 μm orifice. The electrons produced in this way are accelerated by an extraction field to a microchannel
REFERENCES
(1) Cederbaum, L. S.; Zobeley, J.; Tarantelli, F. Giant Intermolecular Decay and Fragmentation of Clusters. Phys. Rev. Lett. 1997, 79, 4778− 4781. (2) Marburger, S.; Kugeler, O.; Hergenhahn, U.; Mö ller, T. Experimental Evidence for Interatomic Coulombic Decay in Ne Clusters. Phys. Rev. Lett. 2003, 90, 203401. (3) Jahnke, T.; Czasch, A.; Schöffler, M. S.; Schössler, S.; Knapp, A.; Käsz, M.; Titze, J.; Wimmer, C.; Kreidi, K.; Grisenti, R. E.; Staudte, A.; Jagutzki, O.; Hergenhahn, U.; Schmidt-Böcking, H.; Dörner, R. Experimental Observation of Interatomic Coulombic Decay in Neon Dimers. Phys. Rev. Lett. 2004, 93, 163401.
1800
dx.doi.org/10.1021/jz400671h | J. Phys. Chem. Lett. 2013, 4, 1797−1801
The Journal of Physical Chemistry Letters
Letter
(4) Hergenhahn, U. Interatomic and Intermolecular Coulombic Decay: The Early Years. J. Electr. Spectr. Relat. Phenom. 2011, 184, 78− 90. (5) Averbukh, V.; Demekhin, P.; Kolorenc, P.; Scheit, S.; Stoychev, S.; Kuleff, A.; Chiang, Y.-C.; Gokhberg, K.; Kopelke, S.; Sisourat, N.; Cederbaum, L. Interatomic Electronic Decay Processes in Singly and Multiply Ionized Clusters. J. Electron Spectrosc. Relat. Phenom. 2011, 183, 36−47. (6) Ö hrwall, G.; Tchaplyguine, M.; Lundwall, M.; Feifel, R.; Bergersen, H.; Rander, T.; Lindblad, A.; Schulz, J.; Peredkov, S.; Barth, S.; Marburger, S.; Hergenhahn, U.; Svensson, S.; Björneholm, O. Femtosecond Interatomic Coulombic Decay in Free Neon Clusters: Large Lifetime Differences between Surface and Bulk. Phys. Rev. Lett. 2004, 93, 173401. (7) Lablanquie, P.; Aoto, T.; Hikosaka, Y.; Morioka, Y.; Penent, F.; Ito, K. Appearance of Interatomic Coulombic Decay in Ar, Kr, and Xe Homonuclear Dimers. J. Chem. Phys. 2007, 127, 154323. (8) Morishita, Y.; Liu, X.-J.; Saito, N.; Lischke, T.; Kato, M.; Prümper, G.; Oura, M.; Yamaoka, H.; Tamenori, Y.; Suzuki, I. H.; et al. Experimental Evidence of Interatomic Coulombic Decay from the Auger Final States in Argon Dimers. Phys. Rev. Lett. 2006, 96, 243402. (9) Barth, S.; Joshi, S.; Marburger, S.; Ulrich, V.; Lindblad, A.; Ö hrwall, G.; Björneholm, O.; Hergenhahn, U. Observation of Resonant Interatomic Coulombic Decay in Ne Clusters. J. Chem. Phys. 2005, 122, 241102. (10) Aoto, T.; Ito, K.; Hikosaka, Y.; Shigemasa, E.; Penent, F.; Lablanquie, P. Properties of Resonant Interatomic Coulombic Decay in Ne Dimers. Phys. Rev. Lett. 2006, 97, 243401. (11) Grieves, G. A.; Orlando, T. M. Intermolecular Coulomb Decay at Weakly Coupled Heterogeneous Interfaces. Phys. Rev. Lett. 2011, 107, 016104. (12) Jahnke, T.; Sann, H.; Havermeier, T.; Kreidi, K.; Stuck, C.; Meckel, M.; Schoeffler, M.; Neumann, N.; Wallauer, R.; Voss, S.; et al. Ultrafast Energy Transfer between Water Molecules. Nat. Phys. 2010, 6, 139−142. (13) Mucke, M.; Braune, M.; Barth, S.; Förstel, M.; Lischke, T.; Ulrich, V.; Arion, T.; Becker, U.; Bradshaw, A.; Hergenhahn, U. A Hitherto Unrecognized Source of Low-Energy Electrons in Water. Nat. Phys. 2010, 6, 143−146. (14) Aziz, E. F.; Ottosson, N.; Faubel, M.; Hertel, I. V.; Winter, B. Interaction between Liquid Water and Hydroxide Revealed by Core− Hole De-excitation. Nature 2008, 455, 89−91. (15) Gokhberg, K.; Kolorenc, P.; Kuleff, A. I.; Cederbaum, L. S. A New Intermolecular Mechanism to Selectively Drive Photoinduced Damages. arXiv.org, e-Print Arch., Phys. (physics.atm-clus) 2013, No. arXiv:1303.6440. (16) Kimura, M.; Fukuzawa, H.; Sakai, K.; Mondal, S.; Kukk, E.; Kono, Y.; Nagaoka, S.; Tamenori, Y.; Saito, N.; Ueda, K. Efficient SiteSpecific Low-Energy Electron Production via Interatomic Coulombic Decay Following Resonant Auger Decay. Phys. Rev. A 2013, 87, 043414. (17) Trinter, F.; Schoffler, M. S.; Kim, H.-K.; Sturm, F.; Cole, K.; Neumann, N.; Vredenborg, A.; Williams, J.; Bocharova, I.; Guillemin, R. Experimental Proof of Resonant Auger Decay Driven Intermolecular Coulombic Decay. Nature 2013, submitted for publication. (18) Saito, N.; Morishita, Y.; Suzuki, I.; Stoychev, S.; Kuleff, A.; Cederbaum, L.; Liu, X.-J.; Fukuzawa, H.; Prumper, G.; Ueda, K. Evidence of Radiative Charge Transfer in Argon Dimers. Chem. Phys. Lett. 2007, 441, 16−19. (19) Cybulski, S. M.; Toczylowski, R. R. Ground State Potential Energy Curves for He2, Ne2, Ar2, He−Ne, He−Ar, and Ne−Ar: A Coupled-Cluster Study. J. Chem. Phys. 1999, 111, 10520−10528. (20) Jolly, W. L.; Hendrickson, D. N. Thermodynamic Interpretation of Chemical Shifts in Core Electron Binding Energies. J. Am. Chem. Soc. 1970, 92, 1863−1871. (21) El-Hadj-Rhouma, M. B.; Berriche, H.; Lakhdar, Z. B.; Spiegelman, F. One-Electron Pseudopotential Calculations of Excited States of LiAr, NaAr, and KAr. J. Chem. Phys. 2002, 116, 1839−1849.
(22) Meyer, M.; v. Raven, E.; Sonntag, B.; Hansen, J. E. Decay of the Ar 2p5 nd Core Resonances: An Autoionization Spectrum Dominated by Shake Processes. Phys. Rev. A 1991, 43, 177−188. (23) de Gouw, J. A.; van Eck, J.; Peters, A. C.; van der Weg, J.; Heideman, H. G. M. Resonant Auger Spectra of the 2p−1 nl States of Argon. J. Phys. B 1995, 28, 2127−2141. (24) Mursu, J.; Aksela, H.; Sairanen, O.-P.; Kivimäki, A.; Nõmmiste, E.; Ausmees, A.; Svensson, S.; Aksela, S. Decay of the 2p54s, 2p53d and 2p54d States of Ar Studied by Utilizing the Auger Resonant Raman Effect. J. Phys. B 1996, 29, 4387−4399. (25) Kimura, M.; Fukuzawa, H.; Tachibana, T.; Yuta Ito, S. M.; Schoffler, M.; Williams, J.; Yuhai Jiang, Y. T.; Saito, N.; Ueda, K. Controlling Low-energy Electron Emission via Resonant-Augerinduced Interatomic Coulombic Decay. J. Phys. Chem. Lett. 2013, DOI: 10.1021/jz4006674. (26) O’Keeffe, P.; Bolognesi, P.; Coreno, M.; Moise, A.; Richter, R.; Cautero, G.; Stebel, L.; Sergo, R.; Pravica, L.; Ovcharenko, Y.; et al. A Photoelectron Velocity Map Imaging Spectrometer for Experiments Combining Synchrotron and Laser Radiations. L. Rev. Sci. Instrum. 2011, 82, 033109. (27) Garcia, G. A.; Nahon, L.; Powis, I. Two-Dimensional Charged Particle Image Inversion using a Polar Basis Function Expansion. Rev. Sci. Instrum. 2004, 75, 4989−4996.
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