1. |
- Burmeister, Florian, et al.
(author)
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Description and performance of an electron-ion coincidence TOF spectrometer used at the Brazilian synchrotron facility LNLS
- 2010
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In: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 180:1-3, s. 6-13
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Journal article (peer-reviewed)abstract
- This paper reports the characteristics and performance of a Time-of-Flight Mass Spectrometer (TOF-MS) for coincidence measurements between electrons and ions that has been developed jointly in Sweden and Brazil. The spectrometer, used for studies of inner-shell photoexcitation of molecules in the gas-phase, has been optimized by implementing ion and electron lenses to allow the use of relatively small diameter detectors. Simulations were performed to understand the lens performance and they show that ions (electrons) could be collected without angular discrimination with a maximum kinetic energy up to ten (two) times higher than without the lens actions. A rotary vacuum chamber allows the spectrometer axis to be positioned at different angles relative to the polarization vector of the excitation beam. An important characteristic of the apparatus is that the acquisition setup allows a multi-hit capability with 1 ns resolution. Hereby, Photoelectron-Photoion-Photoion Coincidence (PEPIPICO) measurements can be performed on molecules containing two or more atoms of equal mass. A method to obtain experimental detection efficiencies of a single ion and one of one, two or three electrons has been developed. A systematic study of the interaction region has been performed to determine the shape of the photon and gas beams. Measurements on molecular nitrogen demonstrate the spectrometer's ability to resolve fragments with the same charge to mass ratio arriving within only a few ns. Simulations and experimental results of fragmentation of two singly charged cation nitrogen atoms agree, confirming that the spectrometer performance is well understood. (C) 2010 Elsevier B.V. All rights reserved.
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2. |
- Ristinmaa Sörensen, Stacey, et al.
(author)
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Site-Selective Participator Decay of Core-Excited Butadiene
- 1996
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 105, s. 10719-10724
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Journal article (peer-reviewed)abstract
- The decay of core-excited electronic states in free 1,3 trans butadiene molecules has been studied using high-resolution synchrotron radiation and electron spectrometry. The core-level energy shift between the terminal and central carbon atoms is 0.64 eV making selective excitation of core electrons from these atoms possible. Resonant excitation to the au(*) valence state leads to autoionizing decay channels which proceed according to the atomic site in the molecule. The radiationless decay is localized, and certain molecular orbitals are excluded from the decay depending upon the site of the core hole. This phenomenon is confirmed by semiempirical INDO calculations based upon the equivalent core approximation. The vibrational structure of the resonances below the carbon K edge has been measured and fit to extract vibrational energies and intensities, chemical shifts, and the lifetimes of the centrally and terminally excited states. The C 1s spectrum is also measured with vibrational resolution and the energies of the normal vibrational modes are extracted. The bond lengths are derived by application of a linear coupling analysis.
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3. |
- Carravetta, V., et al.
(author)
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PH-dependent X-ray Photoelectron Chemical Shifts and Surface Distribution of Cysteine in Aqueous Solution
- 2019
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In: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 123:17, s. 3776-3785
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Journal article (peer-reviewed)abstract
- The distribution and protonation states of amino acids in water droplets are of considerable concern in studies on the formation of clouds in the atmosphere as well as in many biological contexts. In the present work we use the amino acid cysteine as a prototypical example and explore the protonation states of this molecule in aqueous solution, which are strongly affected by the acidity of the environment and also can show different distributions between surface and bulk. We use a combination of X-ray photoelectron chemical shift measurements, density functional theory calculations of the shifts, and reactive force field molecular dynamics simulations of the underlying structural dynamics. We explore how the photoelectron spectra distinctly reflect the different protonation states that are generated by variation of the solution acidity and how the distribution of these protonation states can differ between bulk and surface regions. At specific pH values, we find that the distribution of the cysteine species at the surface is quite different from that in bulk, in particular, for the appearance in the surface region of species which do not exist in bulk. Some ramifications of this finding are discussed.
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4. |
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5. |
- Feifel, R., et al.
(author)
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"Hidden" vibrations in CO : Reinvestigation of resonant Auger decay for the C 1s → π* excitation
- 2002
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In: Physical Review A - Atomic, Molecular, and Optical Physics. - 1050-2947. ; 65:5 A, s. 527011-527018
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Journal article (peer-reviewed)abstract
- The higher vibrational levels of the C 1s→π* excitation in carbon monooxide (CO) were investigated by using resonant Auger electron spectroscopy. The absorption profile of the CO was recorded in the partial electron yield mode. The results showed that the vibrational states were not seen in a total yield absorption spectrum whereas they were shown to be discernable in a partial electron yield spectrum.
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6. |
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7. |
- Grånäs, Oscar, 1979-, et al.
(author)
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Femtosecond fragmentation of CS2 after sulfur 1s ionization : interplay between Auger cascade decay, charge delocalization, and nuclear motion
- 2020
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In: Journal of Physics B. - : IOP PUBLISHING LTD. - 0953-4075 .- 1361-6455. ; 53:24
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Journal article (peer-reviewed)abstract
- We present a combined experimental and theoretical study of the fragmentation of molecular CS2 after sulfur 1s Auger cascade decay, consisting of electron-multi-ion coincidence spectra of charged fragments and theoretical simulations combining density functional theory and molecular dynamics. On the experimental side, a procedure for a complete determination of all sets of ions formed is described. For many of the fragmentation channels, we observed a higher charge in one of the sulfur atoms than the other atoms. Based on these observations and the theoretical simulations where the time scale of the nuclear motion and decay is taken into account, we propose that KLL Auger decay after the 1s core hole creation, via 2p double hole states, results in highly charged and strongly repulsive states with one localized core hole. These localized core holes are sufficiently long-lived that some will decay after fragmentation of the molecular ion, thereby efficiently impeding charge exchange between the fragments.
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8. |
- Le Guen, K., et al.
(author)
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H2S ultrafast dissociation probed by energy-selected resonant Auger electron–ion coincidence measurements
- 2007
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 127:11, s. 114315-
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Journal article (peer-reviewed)abstract
- We have studied the ultrafast dissociation of the H2S molecule upon S 2p(3/2)-> 6a(1) inner-shell excitation by combining high-resolution resonant Auger spectroscopy and energy-selected Auger electron-ion coincidence measurements. Auger final states have been correlated to the different fragmentation pathways (S+, HS+, and H2S+ ions). As an original result, we evidence a three-step mechanism to describe the resonant production of S+: the Auger recombination in the HS* fragment is followed for the A (3)Pi and c (1)Pi states by the S++H fragmentation mechanism.
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9. |
- Andersson, Åke, et al.
(author)
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Experiences with the narrow gap undulator at MAX-lab
- 1995
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In: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 362:2-3, s. 586-591
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Journal article (peer-reviewed)abstract
- An undulator with short poles (period 24 mm) and extremely narrow gap (magnet gap 7.7 mm) using a squeezable vacuum chamber has been installed and is in operation at the MAX-lab 550 MeV storage ring. The device operates with a vacuum chamber aperture down to 6.2 mm. The behaviour of the storage ring concerning lifetime, emittance, tune shift and closed orbit is well described by conventional models. We present here the design of the device, the influence on the storage ring and the spectral characteristics, as well as comparison with expected theoretical results and an overview of the activities at the beam line.
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10. |
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11. |
- Feifel, Raimund, et al.
(author)
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Interference Quenching of v
- 2002
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In: Physical Review Letters. ; 89:10, s. 103002-1
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Journal article (peer-reviewed)
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12. |
- Gisselbrecht, Mathieu, et al.
(author)
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Size dependent fragmentation of argon clusters in the soft x-ray ionization regime.
- 2008
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:4
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Journal article (peer-reviewed)abstract
- Photofragmentation of argon clusters of average size ranging from 10 up to 1000 atoms is studied using soft x-ray radiation below the 2p threshold and multicoincidence mass spectroscopy technique. For small clusters (N=10), ionization induces fast fragmentation with neutral emission imparting a large amount of energy. While the primary dissociation takes place on a picosecond time scale, the fragments undergo slow degradation in the spectrometer on a microsecond time scale. For larger clusters (N>/=100) we believe that we observe the fragmentation pattern of multiply charged species on a time-scale which lasts a few hundred nanoseconds. The reason for these slower processes is the large number of neutral atoms which act as an efficient cooling bath where the excess energy ("heat") dissipates among all degrees of freedom. Further degradation of the photoionic cluster in spectrometer then takes place on the microsecond time scale, similar to small clusters.
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13. |
- K. Wiesner, R. F. Fink, S. L. Sorensen, M. Andersson, R. Feifel, I. Hjelte, C. Miron, A. Naves de Brito, L. Rosenqvist, H. Wang, S. Svensson, O. Björneholm
(author)
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Valence Photoionization and Resonant Core Excitation of Ozone - Experimental and Theoretical Study of the C-State of O3
- 2003
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In: Chem Phys. Lett.. ; :375, s. 76-
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Journal article (peer-reviewed)
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14. |
- Kirschner, Johannes, et al.
(author)
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The molecular structure of the surface of water-ethanol mixtures
- 2021
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In: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 23:19, s. 11568-11578
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Journal article (peer-reviewed)abstract
- Mixtures of water and alcohol exhibit an excess surface concentration of alcohol as a result of the amphiphilic nature of the alcohol molecule, which has important consequences for the physico-chemical properties of water-alcohol mixtures. Here we use a combination of intensity vibrational sum-frequency generation (VSFG) spectroscopy, heterodyne-detected VSFG (HD-VSFG), and core-level photoelectron spectroscopy (PES) to investigate the molecular properties of water-ethanol mixtures at the air-liquid interface. We find that increasing the ethanol concentration up to a molar fraction (MF) of 0.1 leads to a steep increase of the surface density of the ethanol molecules, and an increased ordering of the ethanol molecules at the surface. When the ethanol concentration is further increased, the surface density of ethanol remains more or less constant, while the orientation of the ethanol molecules becomes increasingly disordered. The used techniques of PES and VSFG provide complementary information on the density and orientation of ethanol molecules at the surface of water, thus providing new information on the molecular-scale properties of the surface of water-alcohol mixtures over a wide range of compositions. This information is invaluable in understanding the chemical and physical properties of water-alcohol mixtures.
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15. |
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16. |
- Marinho, R. R.T., et al.
(author)
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Interference between direct and resonant channels in near-resonance photoemission in argon
- 2001
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947. ; 63:3, s. 325141-325145
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Journal article (peer-reviewed)abstract
- The photoelectron spectra of argon was demonstrated during resonant photoemissions. The interference effects of the photoelectron spectra of argon was monitored by following the intensity of final states through resonant and direct channels. The need for a unified one-description of the ionization through a direct and core-excitation mediated channel was described.
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17. |
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18. |
- Miron, C., et al.
(author)
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Nuclear motion driven by the Renner-Teller effect as observed in the resonant Auger decay to the X̃2Π electronic ground state of N2O
- 2001
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 115:2, s. 864-869
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Journal article (peer-reviewed)abstract
- The nuclear dynamics in the Nt 1s→π* in nitrous oxide was studied using the high resolution resonant Auger spectroscopy and ab initio quantum chemical calculations. For probing the nuclear motion of the system in the core-excited state, the frequency detuning technique was used. The results showed changes in vibrational structure for the Auger decay spectra and a strong influence of nuclear motion on the electronic decay.
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19. |
- Rosenqvist, L., et al.
(author)
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Femtosecond dissociation of ozone studied by the Auger Doppler effect
- 2001
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In: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 115:8, s. 3614-3620
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Journal article (peer-reviewed)abstract
- The peaks arising from the decay of the excited oxygen atom were studied. Fast dissociation of core-excited ozone was confirmed by the presence of Auger emission from atomic oxygen in the decay spectrum from the ozone OT 1s-σ*(7a1) state. No such emission was observed after excitation of the corresponding state on the central oxygen atom. An angle-dependent energy shift of the atomic lines was observed. Analysis of the energy shift revealed that the kinetic energy released in the dissociation process is approximately 3.3 ± 0.3eV. An energy release of 8.45 was found by application of a Born-Haber cycle.
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20. |
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21. |
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