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Multi-Electron Coincidence Studies of Atoms and Molecules
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Soft X-Ray Physics.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis concerns multi-ionization coincidence measurements of atoms and small molecules using a magnetic bottle time-of-flight (TOF) spectrometer designed for multi-electron coincidence studies. Also, a time-of-flight mass spectrometer has been used together with the TOF electron  spectrometer for electron-ion coincidence measurements. The multi-ionization processes have been studied by employing a pulsed discharge lamp in the vacuum ultraviolet spectral region and synchrotron radiation in the soft X-ray region. The designs of the spectrometers are described in some detail, and several timing schemes suitable for the light sources mentioned above are presented.

Studies have been performed on krypton, molecular oxygen, carbon disulfide and a series of alcohol molecules. For the latter, double ionization spectra have been recorded and new information has been obtained on the dicationic states. A recently found rule-of-thumb  and quantum chemical calculations have been used to quantify the effective distance of the two vacancies in the dications of these molecules.

For Kr, O2, and CS2, single-photon core-valence spectra have been obtained at the synchrotron radiation facility BESSY II in Berlin and interpreted on the basis of quantum chemical calculations. These spectra show a remarkable similarity to conventional valence photoelectron spectra.

Spectra of triply charged ions were recorded, also at BESSY II, for Kr and CS2 by measuring, in coincidence, all three electrons ejected. The complex transition channels leading to tricationic states were mapped in substantial detail for Kr. It was found that for 3d-ionized krypton, the tricationic states are dominantly populated by cascade Auger decays via distinct intermediate states whose energies have been determined. The triple ionization spectra of CS2 from the direct double Auger effect via S2p, S2s and C1s hole states contain several resolved features and show selectivity based on the initial charge localisation and on the identity of the initial state.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2010. , p. 71
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 743
Keywords [en]
multi-ionization, electron emission, time-of-flight spectroscopy, coincidence spectroscopy, core-valence ionization, synchrotron radiation, electron correlation
National Category
Atom and Molecular Physics and Optics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-122811ISBN: 978-91-554-7805-6 (print)OAI: oai:DiVA.org:uu-122811DiVA, id: diva2:311149
Public defence
2010-05-29, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2010-05-03 Created: 2010-04-20 Last updated: 2013-09-20
List of papers
1. Multielectron coincidence study of the double Auger decay of 3d-ionized krypton
Open this publication in new window or tab >>Multielectron coincidence study of the double Auger decay of 3d-ionized krypton
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2010 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 82, no 4, p. 043418-Article in journal (Refereed) Published
Abstract [en]

Multielectron coincidence data for triple ionization of krypton have been recorded above the 3d ionization threshold at two photon energies (140 and 150 eV). Three principal transition pathways have been observed, two involving double Auger transitions from Kr+, and one involving single Auger transitions from Kr2+ created by direct single-photon double ionization. The decay of the 3d(9) D-2(5/2,3/2) states in Kr+ has been analyzed in some detail and is found to be strongly dominated by cascade processes where two electrons with well-defined energies are emitted. The decay paths leading to the 4s(2)4p(3) S-4, D-2, and P-2 states of Kr3+ are analyzed and energies of seven intermediate states in Kr2+ are given. A preliminary investigation of the decay paths from Kr+ 3d (9)4p(5)nl shake-up states has also been carried out.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-122568 (URN)10.1103/PhysRevA.82.043418 (DOI)000283114900005 ()
Available from: 2010-04-14 Created: 2010-04-14 Last updated: 2017-12-12Bibliographically approved
2. Formation of Kr3+ via core-valence doubly ionized intermediate states
Open this publication in new window or tab >>Formation of Kr3+ via core-valence doubly ionized intermediate states
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2012 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 85, no 3, p. 032502-Article in journal (Refereed) Published
Abstract [en]

The time-of-flight photoelectron-photoion coincidence technique has been used to study single-photon 3d(9)4p(5) core-valence double ionization of Kr and subsequent Auger decay to triply charged states associated with the 4s(2)4p(3) and 4s(1)4p(4) configurations. The photon energy used was h nu = 150 eV. Multiconfiguration Dirac-Fock calculations were performed both for the doubly ionized intermediate states and the triply ionized final states. The intermediate states of Kr2+ are observed between 120 and 125 eV, whereas the final states of Kr3+ are observed between 74- and 120-eV ionization energy. Assignments of all structures are made based on the present numerical results. The calculated Auger rates give a detailed explanation of the relative line strengths observed.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-172032 (URN)10.1103/PhysRevA.85.032502 (DOI)000301104400014 ()
Available from: 2012-04-02 Created: 2012-04-01 Last updated: 2017-12-07Bibliographically approved
3. Double photoionization of alcohol molecules
Open this publication in new window or tab >>Double photoionization of alcohol molecules
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2009 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 80, no 3, p. 032516-Article in journal (Refereed) Published
Abstract [en]

The double valence photoionization spectra of methanol, ethanol, and n-propyl alcohol have been recorded using a time-of-flight photoelectron-photoelectron coincidence technique. The spectra show a well-defined onset followed by broad rounded bands. The lowest vertical double ionization energies have been determined for all molecules and are found to be 32.1, 29.6, and 28.2 eV, respectively. These energies have been applied along with single ionization energies from conventional photoelectron spectra to investigate a recently derived rule of thumb for determination of the lowest double ionization energy in molecules. Many-electron ab initio calculations have been performed on the dicationic ground states in good agreement with the experimental values. For methanol, also excited dicationic states have been calculated up to about 40 eV and used for a detailed interpretation of the experimental spectrum.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-114304 (URN)10.1103/PhysRevA.80.032516 (DOI)000270383900088 ()
Available from: 2010-02-12 Created: 2010-02-12 Last updated: 2017-12-12Bibliographically approved
4. Single-photon core-valence double ionization of molecular oxygen
Open this publication in new window or tab >>Single-photon core-valence double ionization of molecular oxygen
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2008 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 78, no 2, p. 023409-Article in journal (Refereed) Published
Abstract [en]

Single-photon core-valence double ionization of molecular oxygen has been studied using a magnetic bottle time-of-flight electron coincidence spectrometer. The K-1V-1 double ionization electron spectrum of O-2 is reported and is assigned with the aid of ab initio calculations. A direct comparison of the core-valence double ionization electron spectra with the conventional valence band photoelectron spectrum is made. The lowest core-valence double ionization energy is found to be 571.6 eV and is associated with a (3)Pi dicationic state.

Keywords
Autoionization, photoionization, and photodetachment, Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors, Electronic excitation and ionization of molecules; intermediate molecular states
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-107900 (URN)10.1103/PhysRevA.78.023409 (DOI)000259263500009 ()
Note
Part BAvailable from: 2009-09-01 Created: 2009-08-31 Last updated: 2017-12-13Bibliographically approved
5. Core-valence double photoionization of the CS2 molecule
Open this publication in new window or tab >>Core-valence double photoionization of the CS2 molecule
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2010 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 133, no 9, p. 094305-Article in journal (Refereed) Published
Abstract [en]

Double photoionization spectra of the CS2 molecule have been recorded using the TOF-PEPECO technique in combination with synchrotron radiation at the photon energies h nu=220, 230, 240, 243, and 362.7 eV. The spectra were recorded in the S 2p and C 1s inner-shell ionization regions and reflect dicationic states formed out of one inner-shell vacancy and one vacancy in the valence region. MCSCF calculations were performed to model the energies of the dicationic states. The spectra associated with a S 2p vacancy are well structured and have been interpreted in some detail by comparison to conventional S 2p and valence photoelectron spectra. The lowest inner-shell-valence dicationic state is observed at the vertical double ionization energy 188.45 eV and is associated with a (2p(3/2))(-1)(2 pi(g))(-1) double vacancy. The spectrum connected to the C 1s vacancy shows a distinct line at 310.8 eV, accompanied by additional broad features at higher double ionization energies. This line is associated with a (C 1s)(-1)(2 pi(g))(-1) double vacancy.

Keywords
carbon compounds, inner-shell ionisation, molecule-photon collisions, photoionisation, SCF calculations
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-122570 (URN)10.1063/1.3469812 (DOI)000281742900011 ()
Available from: 2010-04-20 Created: 2010-04-14 Last updated: 2017-12-12Bibliographically approved
6. Spectra of the triply charged ion CS[sub 2][sup 3+] and selectivity in molecular Auger effects
Open this publication in new window or tab >>Spectra of the triply charged ion CS[sub 2][sup 3+] and selectivity in molecular Auger effects
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2010 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 132, no 10, p. 104311-Article in journal (Refereed) Published
Abstract [en]

Spectra of triply charged carbon disulphide have been obtained by measuring, in coincidence, all three electrons ejected in its formation by photoionization. Measurements of the CS23+ ion in coincidence with the three electrons identify the energy range where stable trications are formed. A sharp peak in this energy range is identified as the 2Π ground state at 53.1±0.1 eV, which is the lowest electronic state according to ab initio molecular orbital calculations. Triple ionization by the double Auger effect is provisionally divided, on the basis of the pattern of energy sharing between the two Auger electrons into contributions from direct and cascade Auger processes. The spectra from the direct double Auger effect via S 2p, S 2s, and C 1s hole states contain several resolved features and show selectivity based on the initial charge localization and on the identity of the initial state. Triple ionization spectra from single Auger decay of S 2p -based core-valence states CS22+ show retention of the valence holes in this Auger process. Related ion-electron coincidence measurements give the triple ionization yields and the breakdown patterns in triple photoionization at selected photon energies from 90 eV to above the inner shell edges.

Keywords
ab initio calculations, Auger effect, carbon compounds, molecule-photon collisions, orbital calculations, photoionisation, positive ions, time of flight spectra
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-121766 (URN)10.1063/1.3352549 (DOI)000275589700025 ()
Available from: 2010-03-30 Created: 2010-03-30 Last updated: 2017-12-12Bibliographically approved

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