| 1. |
- Iablonskyi, D., et al.
(author)
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Interatomic Coulombic Decay Processes after Multiple Valence Excitations in Ne Clusters
- 2015
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In: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6596 .- 1742-6588. ; 635, s. 112067-112067
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Conference paper (peer-reviewed)abstract
- We present a comprehensive analysis of autoionization processes in Ne clusters (similar to 5000 atoms) after multiple valence excitations by free electron laser radiation. The evolution from 2-body interatomic Coulombic decay (ICD) to 3-body ICD is demonstrated when changing from surface to bulk Frenkel exciton excitation. Super Coster-Kronig type 2-body ICD is observed at Wannier exciton which quenches the main ICD channel.
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| 2. |
- Iablonskyi, D., et al.
(author)
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Slow Interatomic Coulombic Decay of Multiply Excited Neon Clusters
- 2016
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In: Physical Review Letters. - 0031-9007. ; 117:27
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Journal article (peer-reviewed)abstract
- Ne clusters (∼5000 atoms) were resonantly excited (2p→3s) by intense free electron laser (FEL) radiation at FERMI. Such multiply excited clusters can decay nonradiatively via energy exchange between at least two neighboring excited atoms. Benefiting from the precise tunability and narrow bandwidth of seeded FEL radiation, specific sites of the Ne clusters were probed. We found that the relaxation of cluster surface atoms proceeds via a sequence of interatomic or intermolecular Coulombic decay (ICD) processes while ICD of bulk atoms is additionally affected by the surrounding excited medium via inelastic electron scattering. For both cases, cluster excitations relax to atomic states prior to ICD, showing that this kind of ICD is rather slow (picosecond range). Controlling the average number of excitations per cluster via the FEL intensity allows a coarse tuning of the ICD rate.
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| 3. |
- Takanashi, T, et al.
(author)
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Time-Resolved Measurement of Interatomic Coulombic Decay Induced by Two-Photon Double Excitation of Ne2
- 2017
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In: Physical Review Letters. - 0031-9007. ; 118:3
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Journal article (peer-reviewed)abstract
- The hitherto unexplored two-photon doubly excited states [Ne∗(2p-13s)]2 were experimentally identified using the seeded, fully coherent, intense extreme ultraviolet free-electron laser FERMI. These states undergo ultrafast interatomic Coulombic decay (ICD), which predominantly produces singly ionized dimers. In order to obtain the rate of ICD, the resulting yield of Ne2+ ions was recorded as a function of delay between the extreme ultraviolet pump and UV probe laser pulses. The extracted lifetimes of the long-lived doubly excited states, 390(-130/+450) fs, and of the short-lived ones, less than 150 fs, are in good agreement with ab initio quantum mechanical calculations.
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| 4. |
- Alagia, M, et al.
(author)
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Angular effects in autoionization of 3 P doubly excited states in He
- 2009
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In: Journal of Physics: Conference Series. ; 194
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Journal article (peer-reviewed)abstract
- The first members of dipole allowed 3 P o doubly excited series in helium have been observed in resonant photoexcitation of 1 s 2 s 3 S e metastable atoms. A good agreement measured relative photoionization cross sections is achieved when theory includes the radiation damping and, also important, the effects of spin-orbit multiplet splitting on electron angular distribution.
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| 5. |
- Alagia, M., et al.
(author)
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Excitation of 1S and 3S Metastable Helium Atoms to Doubly Excited States
- 2009
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:15, s. 153001-
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Journal article (peer-reviewed)abstract
- We present spectra of triplet and singlet metastable helium atoms resonantly photoexcited to doubly excited states. The first members of three dipole-allowed 1,3Po series have been observed and their relative photoionization cross sections determined, both in the triplet (from 1s2s 3Se) and singlet (from 1s2s 1Se) manifolds. The intensity ratios are drastically different with respect to transitions from the ground state. When radiation damping is included the results for the singlets are in agreement with theory, while for triplets spin-orbit interaction must also be taken into account.
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| 6. |
- Soderstrom, J, et al.
(author)
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X-ray-emission-threshold-electron coincidence spectroscopy
- 2004
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048. ; 141:2-3, s. 161-170
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Journal article (peer-reviewed)abstract
- Using a penetration-field threshold photoelectron (TPE) analyzer and efficient photon detectors X-ray-emission-threshold-electron coincidence (XETECO) spectroscopy has been developed to a point where peak shape analysis becomes meaningful. The spectra can, on the present level of accuracy, be interpreted as conventional TPE spectra free from post collision interaction effects. For the neon atom and the nitrogen molecule we find a detailed correspondence with state-of-the-art photoemission spectra, both regarding peak positions, line shapes, and relative intensities. Intensity redistribution due to fast core vacancy rearrangement processes in systems with close-lying core levels, like O-2, N2O, and NO is briefly discussed. It is demonstrated that even the complex threshold behavior at the F K threshold in SF6 leads to a well-defined XETECO peak, directly corresponding to classical photoemission results. (C) 2004 Elsevier B.V. All rights reserved.
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| 7. |
- Alagia, M., et al.
(author)
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Probing the potential energy surface by highresolution x-ray absorption spectroscopy : The umbrella motion of the coreexcited CH3 free radical
- 2007
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In: Physical Review. A. - 1050-2947 .- 1094-1622. ; 76:2, s. 124305-
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Journal article (peer-reviewed)abstract
- A detailed study of the umbrellalike vibration in inner-shell spectroscopy is presented. The high-resolution x-ray absorption spectrum for the lowest lying core excitation of the CH3 free radical was recorded. High quality potential energy surfaces (PES) for the initial and final states of the transition were calculated as a function of the symmetrical stretching and the umbrella deformation coordinates. The strong anharmonicity along the umbrella coordinate in the double-well region of the PES of the core excited state has a strong effect on the bending vibrational progressions. The excellent agreement between the experiment and theory allows an accurate spectroscopic characterization of the vibrational structure of the electronic transition, and the estimation of the umbrella inversion time of 149 fs.
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| 8. |
- Ekström, Ulf, et al.
(author)
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The umbrella motion of core-excited CH3 and CD3 methyl radicals
- 2008
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In: Journal of Chemical Physics. - College Park, MD United States : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 128:4, s. 044302-1-044302-11
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Journal article (peer-reviewed)abstract
- An accurate experimental and theoretical study of the lowest core excitationof CH3 and CD3 methyl radicals is presented. The complexvibrational structure of the lowest band of the x-ray absorptionspectrum (XAS) is due to the large variation of themolecular geometry, which is planar in the ground state andpyramidal in the core-excited state. The XAS spectra of thetwo radicals were recorded at high resolution and assigned bytheoretical simulations of the spectra, taking into account the couplingof symmetrical stretching and symmetrical bending (umbrellalike) deformations of theradicals. An excellent agreement between experimental and theoretical spectral profilesallowed us to accurately characterize the vibrational structure of theelectronic transition. The similarities, as well as the differences, ofthe peculiar vibrational progression observed for the two radicals areexplained by the strong anharmonicity along the umbrella coordinate andby the isotopic variation, leading to a different probing ofthe double-well potential energy surface of the core excited stateduring the nuclear motion.
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| 9. |
- Gorczyca, TW, et al.
(author)
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Radiative and relativistic effects in the decay of highly excited states in helium
- 2000
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In: PHYSICAL REVIEW LETTERS. - : AMERICAN PHYSICAL SOC. - 0031-9007. ; 85:6, s. 1202-1205
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Journal article (peer-reviewed)abstract
- A recent experimental study [J.-E. Rubensson et al., Phys. Rev. Lett. 83, 947 (1999)] measured a significant fluorescence yield of the He(2lnl') photoexcited resonances, showing major qualitative differences from nonrelativistic predictions. We present a
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| 10. |
- Rubensson, Jan-Erik, et al.
(author)
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Influence of the Radiative Decay on the Cross Section for Double Excitations in Helium
- 1999
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 83:5, s. 947-950
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Journal article (peer-reviewed)abstract
- The fluorescence yield spectrum of the double excitations in helium has been measured. All three Rydberg series converging to the N = 2 threshold are resolved, and the intensity of the individual lines is determined. The intensity variation through each series indicates that the radiative decay channel cannot be neglected when discussing the double excitations in helium. This calls for a revision of the interpretation of the absorption spectrum, and sets the limit for using the ion yield method to monitor the absorption probability.
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| 11. |
- Salén, Peter, et al.
(author)
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Complete dissociation branching fractions and Coulomb explosion dynamics of SO2 induced by excitation of O 1s pre-edge resonances
- 2015
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 143:13
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Journal article (peer-reviewed)abstract
- Fragmentation processes of SO2 following excitation of the six main O 1s pre-edge resonances, as well as above the ionization threshold and below the resonances, are studied using a position-sensitive time-of-flight ion imaging detector, and the associated dissociation branching ratios and break-up dynamics are determined. In order to distinguish between the O+ and S2+ fragments of equal mass-to-charge ratio, the measurements have been performed with the isotopically enriched (SO2)-O-18 sample. By analysis of the complete set of the fragment momentum vectors, the beta values for the fragments originating from the SO+ + O+ break-up and the kinetic energy release for fragmentation channels of both SO22+ and SO23+ parent ions are determined. We also present results on the three-body break-up dynamics. (C) 2015 AIP Publishing LLC.
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| 12. |
- Schio, L., et al.
(author)
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A Study of H2O2 with Threshold Photoelectron Spectroscopy (TPES) and Electronic Structure Calculations: Redetermination of the First Adiabatic Ionization Energy (AIE)
- 2016
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In: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 120:27, s. 5220-5229
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Journal article (peer-reviewed)abstract
- In this work, hydrogen peroxide has been studied with threshold photoelectron (TPE) spectroscopy and photoelectron (PE) spectroscopy. The TPE spectrum has been recorded in the 10.0-21.0 eV ionization energy region, and the PE spectrum has been recorded at 21.22 eV photon energy. Five bands have been observed which have been assigned on the basis of UCCSD(T)-F12/VQZ-F12 and IP-EOM CCSD calculations. Vibrational structure has only been resolved in the TPE spectrum of the first band, associated with the (X) over tilde (2)Bg H2O2+ <- (X) over tilde (1)A H2O2 ionization, on its low energy side. This structure is assigned with the help of harmonic Franck-Condon factor calculations that use the UCCSD(T)-F12a/VQZ-F12 computed adiabatic ionization energy (AIE), and UCCSD(T)-F12a/VQZ-F12 computed equilibrium geometric parameters and harmonic vibrational frequencies for the H2O2 (X) over tilde (1)A state and the H2O2 (X) over tilde (2)Bg state. These calculations show that the main vibrational structure on the leading edge of the first TPE band is in the O-O stretching mode (omega(3)) and the HOOH deformation mode (omega(4)), and comparison of the simulated spectrum to the experimental spectrum gives the first AIE of H2O2 as (10.685 +/- 0.005) eV and omega(4) = (850 +/- 30) and omega(3) = (1340 +/- 30) cm(-1) in the (X) over tilde (2)Bg state of H2O2+. Contributions from ionization of vibrationally excited levels in the torsion mode have been identified in the TPE spectrum of the first band and the need for a vibrationally resolved TPE spectrum from vibrationally cooled molecules, as well as higher level Franck-Condon factors than performed in this work, is emphasized.
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| 13. |
- Schio, L., et al.
(author)
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Double Photoionization of Nitrosyl Chloride by Synchrotron Radiation in the 24-70 eV Photon Energy Range
- 2023
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In: Molecules. - 1420-3049. ; 28:13
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Journal article (peer-reviewed)abstract
- The behavior of nitrosyl chloride (ClNO) exposed to ionizing radiation was studied by direct probing valence-shell electrons in temporal coincidence with ions originating from the fragmentation process of the transient ClNO2+. Such a molecular dication was produced by double photoionization with synchrotron radiation in the 24-70 eV photon energy range. The experiment has been conducted at the Elettra Synchrotron Facility of Basovizza (Trieste, Italy) using a light beam linearly polarized with the direction of the polarization vector parallel to the ClNO molecular beam axis. ClNO molecules crossing the photon beam at right angles in the scattering region are generated by effusive expansion and randomly oriented. The threshold energy for the double ionization of ClNO (30.1 & PLUSMN; 0.1 eV) and six dissociation channels producing NO+/Cl+, N+/Cl+, N+/O+, O+/Cl+, ClN+/O+, NO+/Cl2+ ion pairs, with their relative abundance and threshold energies, have been measured.
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| 14. |
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| 15. |
- Hansen, Klavs, 1958, et al.
(author)
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Single photon thermal ionization of large molecules
- 2017
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In: Elettra Highlights.
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Journal article (other academic/artistic)abstract
- We have demonstrated that gas phase C60 can ionize in a quasi-thermal process where the absorption of a single photon at energies of several tens of eVs leads to the formation of a transient hot electron gas, while the vibrational degrees of freedom remain cold. The existence of the hot electron gas is signalled by the emission of thermal electrons with Boltzmann-like kinetic energy distributions with temperatures of 10000−20000 K. The ionization mechanism is expected to be general for large molecules and will have, e.g., astrophysical consequences.
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| 16. |
- Li, C., et al.
(author)
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Experimental and theoretical XPS and NEXAFS studies of N-methylacetamide and N-methyltrifluoroacetamide
- 2016
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In: Physical Chemistry Chemical Physics - PCCP. - 1463-9076. ; 18
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Journal article (peer-reviewed)abstract
- Experimental Near-Edge X-ray Absorption Fine-Structure (NEXAFS) spectra of N-methyltrifluoroacetamide (FNMA), which is a peptide model system, measured at the C, N, O and F K-edges are reported. The features in the spectra have been assigned by Static-Exchange (STEX) calculations. Using the same method, we have also assigned previously measured NEXAFS spectra of another peptide model system, N-methylacetamide (NMA). To facilitate the NEXAFS feature assignments, X-ray Photoelectron Spectroscopy (XPS) measurements for NMA and FNMA have been carried out with the aim of obtaining the 1s electron ionization potentials, which are compared with the values predicted by our Hartree–Fock (ΔHF) and Multi Configuration Self Consistent Field (ΔMCSCF) calculations. We also demonstrate an approach to compensate for screening effects that are neglected in the STEX method. Ion yield measurements of FNMA associated with the excitation of several C, N, O, and F K-shell pre-edge resonances have revealed site-specific fragmentation in some cases which we interpret with the aid of our theoretical calculations.
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| 17. |
- Salén, Peter, et al.
(author)
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NEXAFS spectroscopy and site-specific fragmentation of N-methylformamide, N,N-dimethylformamide, and N,N-dimethylacetamide
- 2016
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 144:24
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Journal article (peer-reviewed)abstract
- Near-edge X-ray absorption fine-structure (NEXAFS) spectra measured at the C, N, and O K-edges for three molecules containing the amide moiety, N-methylformamide (HCONHCH3), N,N-dimethylformamide (HCON(CH3)(2)), and N,N-dimethylacetamide (CH3CON(CH3)(2)) are presented. These molecules have similar structures and differ by the number of methyl groups located at the molecular ends. The fragmentation of these molecules after resonant excitation at different K-edge resonances is also investigated, using a 3D-ion imaging time-of-flight spectrometer. A comparison between the molecules with respect to the relative contributions of the fragments created upon excitation at distinct resonances reveals site-specific fragmentation. Further information about the character of the core-excitation and dissociation process is obtained from the angular distributions of the ion fragments. Published by AIP Publishing.
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