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Studies of Single and Multiple Ionization Processes in Rare Gases and some Small Molecules
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis various aspects of photoionization are investigated with respect to both single and multiple electron emission from atoms and molecules. The studies include both valence and core levels and involve transitions which leave the atoms or molecules in various charge states.

S2p electrons in the CS2 molecule were excited into Rydberg orbitals close to the ionization threshold. Subsequent autoionization leads to the emission of single electrons which were detected by a conventional electron spectrometer, bringing the molecule into various cationic states characterized by two valence holes and a Rydberg spectator electron. Vibrational progressions have been assigned as excitations of the totally symmetric v1 and the asymmetric stretching v3 modes in the cationic states.

Double ionization spectra of the CS2 molecule were recorded in the S2p and C1s innershell ionization regions using a magnetic bottle many-electron coincidence spectrometer, revealing dicationic states formed out of one inner-shell vacancy and one vacancy in the valence region. The spectrum connected to the S2p vacancy is richly structured in contrast to the spectrum connected to the C1s vacancy, which shows essentially one distinct band.

The development of a new variant of the magnetic bottle coincidence technique tailored for valence triple photoionization studies of rare gas atoms at synchrotron radiation sources is presented, overcoming the problem of high repetition rate in single-bunch operation of the storage ring. The studies of the rare gas atoms confirm that a correction of the lowest triple-ionization energy of Kr, currently listed in standard tables, is needed.

Also, single-site N1s and O1s double core ionization of the NO and N2O molecules and single-site O1s, C1s and S2p double core ionization of the OCS molecule has been studied with the magnetic bottle technique. Double core holes are of particular interest due to putatively larger chemical shifts compared to single core holes. The observed ratio between the double and single ionization energies are in all cases close or equal to 2.20.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2014. , 55 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1132
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-221128ISBN: 978-91-554-8910-6 (print)OAI: oai:DiVA.org:uu-221128DiVA: diva2:707817
Public defence
2014-05-16, sal 80121, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (Swedish)
Opponent
Supervisors
Available from: 2014-04-24 Created: 2014-03-25 Last updated: 2014-04-29Bibliographically approved
List of papers
1. An x-ray absorption and a normal Auger study of the fine structure in the S2p(-1) region of the CS2 molecule
Open this publication in new window or tab >>An x-ray absorption and a normal Auger study of the fine structure in the S2p(-1) region of the CS2 molecule
2009 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 42, no 8, 085102- p.Article in journal (Refereed) Published
Abstract [en]

The photoabsorption spectrum of the CS2 molecule has been recorded in the vicinity of the two S2p(3/2,1/2) ionization limits at 169.806 eV and 171.075 eV. Synchrotron radiation was used with photon energies covering the energy range between 160 eV and 175 eV. Extensive structure is observed below the ionization limits. It is associated with transitions to both valence and Rydberg states. The latter contain vibrational fine structure due to excitations of the nu(3) asymmetric stretching mode. The vibrational energy is approximately 195 meV in close agreement with previous results obtained from photoelectron spectra for the S2p(3/2,1/2) single-hole states. Above the ionization limits, a resonance is observed in the ionization continuum. An electron spectrum recorded on top of this resonance reveals S2p(-1) VV Auger transitions at high resolution.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-129137 (URN)10.1088/0953-4075/42/8/085102 (DOI)000265031200010 ()
Available from: 2010-08-09 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Cationic Rydberg states observed in resonantly enhanced electron spectra of CS2
Open this publication in new window or tab >>Cationic Rydberg states observed in resonantly enhanced electron spectra of CS2
2009 (English)In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 355, no 1, 55-61 p.Article in journal (Refereed) Published
Abstract [en]

The inner valence electron spectrum of the CS2 Molecule has been investigated in the binding energy range between 18.6 and 26.3 eV using synchrotron radiation for ionisation. Photon energies in the range from 67 to about 167 eV have been used, with particular focus on 166.70, 166.89 and 167.09 eV for which S2p electrons are resonantly transferred into Rydberg orbitals close to the ionisation threshold. From there, autoionisation takes the molecule into various cationic states characterized by two valence holes and a Rydberg spectator electron. Many new bands are observed which contain vibrational progressions with spacings around 120 meV in most cases. These are assigned as excitations of the totally symmetric stretching v, mode in the cationic state. The new bands reflect states in the cation that are close to the electronic states of the dication and assignments are made by comparison to double ionisation electron spectra.

Keyword
CS2, Electron spectroscopy, Autoionisation, Inner valence region, Rydberg series, Vibrational structure
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-137364 (URN)10.1016/j.chemphys.2008.11.007 (DOI)000262801500010 ()
Available from: 2010-12-15 Created: 2010-12-15 Last updated: 2017-12-11Bibliographically approved
3. 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, 094305- p.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.

Keyword
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
4. Coincidence technique using synchrotron radiation for triple photoionization: Results on rare gas atoms
Open this publication in new window or tab >>Coincidence technique using synchrotron radiation for triple photoionization: Results on rare gas atoms
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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 6, 063423- p.Article in journal (Refereed) Published
Abstract [en]

Final-state trication spectra and electron distributions produced by soft x-ray single-photon triple ionization of rare gas atoms have been obtained by a multiple-coincidence technique using storage-ring synchrotron radiation. The technique uses electron time of flight with ion detection to overcome the problem of high repetition rates in single-bunch operation. A correction needed to the triple-ionization energy of Kr currently listed in standard tables is confirmed, and the method’s ability to examine the three-electron distributions, characterizing the ionization mechanisms and post-collision interactions, is illustrated.

Keyword
atom-photon collisions, krypton, photoionisation, time of flight spectra
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-114309 (URN)10.1103/PhysRevA.78.063423 (DOI)000262243500025 ()
Available from: 2010-02-12 Created: 2010-02-12 Last updated: 2017-12-12Bibliographically approved
5. N1s and O1s double ionization of the NO and N2O molecules
Open this publication in new window or tab >>N1s and O1s double ionization of the NO and N2O molecules
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2014 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 4, 044309- p.Article in journal (Refereed) Published
Abstract [en]

Single-site N1s and O1s double core ionisation of the NO and N2O molecules has been studied using a magnetic bottle many-electron coincidence time-of-flight spectrometer at photon energies of 1100 eV and 1300 eV. The double core hole energies obtained for NO are 904.8 eV (N1s(-2)) and 1179.4 eV (O1s(-2)). The corresponding energies obtained for N2O are 896.9 eV (terminal N1s(-2)), 906.5 eV (central N1s(-2)), and 1174.1 eV (O1s(-2)). The ratio between the double and single ionisation energies are in all cases close or equal to 2.20. Large chemical shifts are observed in some cases which suggest that reorganisation of the electrons upon the double ionization is significant. Delta-self-consistent field and complete active space self-consistent field (CASSCF) calculations were performed for both molecules and they are in good agreement with these results. Auger spectra of N2O, associated with the decay of the terminal and central N1s(-2) as well as with the O1s(-2) dicationic states, were extracted showing the two electrons emitted as a result of filling the double core holes. The spectra, which are interpreted using CASSCF and complete active space configuration interaction calculations, show atomic-like character. The cross section ratio between double and single core hole creation was estimated as 1.6 x 10(-3) for nitrogen at 1100 eV and as 1.3 x 10(-3) for oxygen at 1300 eV. (C) 2014 AIP Publishing LLC.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-220812 (URN)10.1063/1.4853655 (DOI)000331211700035 ()
Available from: 2014-03-21 Created: 2014-03-20 Last updated: 2017-12-05Bibliographically approved
6. Single site double core level ionization of OCS
Open this publication in new window or tab >>Single site double core level ionization of OCS
(English)Article in journal (Other academic) Submitted
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:uu:diva-221114 (URN)
Available from: 2014-03-25 Created: 2014-03-25 Last updated: 2014-04-24Bibliographically approved

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