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Single-photon multiple ionisation of atoms and molecules investigated by coincidence spectroscopy: Site-specific effects in acetaldehyde and carbon dioxide
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and Condensed Matter Physics. Department of Physics, University of Gothenburg, Origovägen 6B, SE-412 96 Gothenburg, Sweden.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, multiple ionisation processes of free atoms and molecules upon single photon absorption are studied by means of a versatile multi-electron-ion coincidence spectroscopy method based on a magnetic bottle, primarily in combination with synchrotron radiation. The latter offered the possibility to access not only valence but also core levels, revealing processes, which promote the target systems into different charge states.

One study focuses on double and triple ionisation processes of acetaldehyde (ethanal) in the valence region as well as single and double Auger decay of initial 1s core vacancies. The latter are investigated site-selectively for the two chemically different carbon atoms of acetaldehyde, scrutinising theoretical predictions specifically made for that system.

A related study concentrates on core-valence double ionisation spectra of acetaldehyde, which have been investigated in the light of a previously established empirical model, and which have been used as test cases for analysing this kind of spectra by means of quantum chemical electronic structure methods of increasing sophistication.

A third study investigates site-specific fragmentation upon 1s photoionisation of acetaldehyde using a magnetic bottle augmented with an in-line ion time-of-flight mass spectrometer. Experimental evidence is presented that bond rupture occurs with highest probability in the vicinity of the initial charge localisation and possible mechanisms are discussed. A site-specificity parameter P is introduced to show that differences in fragmentation behavior between initial ionisations at chemically different carbon atoms probably persist even for identical internal energy contents in the nascent dications.

In another study where both electrons and ions from Auger decay of core-excited and core-ionised states of CO2 are detected in coincidence, it is confirmed that O2+ is formed specifically in Auger decay from the C1s → π* and O1s → π* resonances, suggesting a decisive role of the π* orbital in the molecular rearrangement. Also, the molecular rearrangement is found to occur by bending in the resonant states, and O2+ is produced by both single and double Auger decay.

A new version of the multi-electron-ion coincidence method, where the ion time-of-flight spectrometer is mounted perpendicularly to the electron flight tube, which affects less the electron resolution and which allows for position sensitive detection of the ions, is employed in combination with tunable soft X-rays to reveal the branching ratios to final Xen+ states with 2 < n < 9 from pure 4d-1, 4p-1, 4s-1, 3d-1 and 3p-1 Xe+ hole states. The coincident electron spectra give information on the Auger cascade pathways.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 84 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1410
Keyword [en]
acetaldehyde, carbon dioxide, xenon, electron correlation, double ionisation, triple ionisation, core-valence ionisation, site-specific Auger decay, multiple Auger decay, branching ratios, site-specific photodissociation, molecular rearrangement, time-of-flight multi-electron-ion coincidence spectroscopy, synchrotron radiation
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-301128ISBN: 978-91-554-9665-4OAI: oai:DiVA.org:uu-301128DiVA: diva2:953705
Public defence
2016-09-30, Häggsalen, Ångstömlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2016-09-09 Created: 2016-08-18 Last updated: 2016-09-21
List of papers
1. Single-photon double and triple ionization of acetaldehyde (ethanal) studied by multi-electron coincidence spectroscopy
Open this publication in new window or tab >>Single-photon double and triple ionization of acetaldehyde (ethanal) studied by multi-electron coincidence spectroscopy
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2015 (English)In: Chemical Physics, ISSN 0301-0104, E-ISSN 1873-4421, Vol. 463, 159-168 p.Article in journal (Refereed) Published
Abstract [en]

Single-photon multiple ionization processes of acetaldehyde (ethanal) have been experimentally investigated by utilizing a multi-particle coincidence technique based on the time-of-flight magnetic bottle principle, in combination with either a synchrotron radiation source or a pulsed helium discharge lamp. The processes investigated include double and triple ionization in the valence region as well as single and double Auger decay of core-ionized acetaldehyde. The latter are studied site-selectively for chemically different carbon core vacancies, scrutinizing early theoretical predictions specifically made for the case of acetaldehyde. Moreover, Auger processes in shake-up and core-valence ionized states are investigated. In the cases where the processes involve simultaneous emission of two electrons, the distributions of the energy sharing are presented, emphasizing either the knock-out or shake-off mechanism.

Keyword
Acetaldehyde, Double ionization, Triple ionisation, Site-specific Auger decay
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-270927 (URN)10.1016/j.chemphys.2015.10.006 (DOI)000365582100021 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationEU, European Research Council, R II 3-CT-2004-506008
Available from: 2016-01-05 Created: 2016-01-05 Last updated: 2016-08-25Bibliographically approved
2. An experimental and theoretical study of core-valence double ionisation of acetaldehyde (ethanal)
Open this publication in new window or tab >>An experimental and theoretical study of core-valence double ionisation of acetaldehyde (ethanal)
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2016 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, no 4, 2535-2547 p.Article in journal (Refereed) Published
Abstract [en]

Core-valence double ionisation spectra of acetaldehyde (ethanal) are presented at photon energies above the carbon and oxygen 1s ionisation edges, measured by a versatile multi-electron coincidence spectroscopy technique. We use this molecule as a testbed for analyzing core-valence spectra by means of quantum chemical calculations of transition energies. These theoretical approaches range from two simple models, one based on orbital energies corrected by core valence interaction and one based on the equivalent core approximation, to a systematic series of quantum chemical electronic structure methods of increasing sophistication. The two simple models are found to provide a fast orbital interpretation of the spectra, in particular in the low energy parts, while the coverage of the full spectrum is best fulfilled by correlated models. CASPT2 is the most sophisticated model applied, but considering precision as well as computational costs, the single and double excitation configuration interaction model seems to provide the best option to analyze core-valence double hole spectra.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-281987 (URN)10.1039/c5cp05758b (DOI)000369506000030 ()26700657 (PubMedID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationEU, European Research Council, R II 3-CT-2004-506008Swedish National Infrastructure for Computing (SNIC), SNIC 023/07-18
Available from: 2016-04-01 Created: 2016-04-01 Last updated: 2016-08-25Bibliographically approved
3. Mechanisms of site-specific photochemistry following core-shell ionization of chemically inequivalent carbon atoms in acetaldehyde (ethanal)
Open this publication in new window or tab >>Mechanisms of site-specific photochemistry following core-shell ionization of chemically inequivalent carbon atoms in acetaldehyde (ethanal)
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2016 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690Article in journal (Refereed) Submitted
Abstract [en]

Site-specific fragmentation upon 1s photoionisation of acetaldehyde has been studied using synchrotron radiation and a multi-electron-ion coincidence technique based on a magnetic bottle. Experimental evidence is presented that bond rupture occurs with highest probability in the vicinity of the initial charge localisation and possible mechanisms are discussed. We find that a significant contribution to site-specific photochemistry is made by different fragmentation patterns of individual quantum states populated at identical ionisation energies.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-301121 (URN)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationEU, European Research Council, R II 3-CT-2004-506008Swedish National Infrastructure for Computing (SNIC), SNIC 023/07-18
Available from: 2016-08-18 Created: 2016-08-18 Last updated: 2016-08-25Bibliographically approved
4. Carbon dioxide ion dissociations after inner shell excitation and ionization: The origin of site-specific effects
Open this publication in new window or tab >>Carbon dioxide ion dissociations after inner shell excitation and ionization: The origin of site-specific effects
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2014 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 140, no 18, 184305- p.Article in journal (Refereed) Published
Abstract [en]

Multi-coincidence experiments with detection of both electrons and ions from decay of core-excited and core-ionized states of CO2 confirm that O-2(+) is formed specifically in Auger decay from the C1s-pi* and O1s-pi* resonances. Molecular rearrangement occurs by bending in the resonant states, and O-2(+) is produced by both single and double Auger decay. It is suggested that electron capture by C+ after partial dissociation in the doubly ionized core of excited CO2+, formed by shake-up in spectator resonant Auger decay, accounts for high kinetic energy and high internal energy in some C + O-2(+) fragments.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-228478 (URN)10.1063/1.4872218 (DOI)000336782700069 ()
Available from: 2014-07-15 Created: 2014-07-15 Last updated: 2016-08-25Bibliographically approved
5. Ion charge-resolved branching in decay of inner shell holes in Xe up to 1200eV
Open this publication in new window or tab >>Ion charge-resolved branching in decay of inner shell holes in Xe up to 1200eV
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2015 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 48, no 20, 205001Article in journal (Refereed) Published
Abstract [en]

Using a new multi-electron multi-ion coincidence apparatus and soft x-ray synchrotron radiation we have determined branching ratios to final Xen+ states with 2 < n < 9 from the 4d(-1), 4p(-1), 4s(-1), 3d(-1) and 3p(-1) Xe+ hole states. The coincident electron spectra give information on the Auger cascade pathways. We show that by judicious choice of coincident electrons, almost pure single charge states of the final ions can be selected.

Keyword
inner shell holes, multiple Auger decay, branching ratios, coincidence detection
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-265810 (URN)10.1088/0953-4075/48/20/205001 (DOI)000362421800008 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationEU, FP7, Seventh Framework Programme, 312284
Available from: 2015-11-03 Created: 2015-11-03 Last updated: 2016-08-25Bibliographically approved

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