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Mechanisms of site-specific photochemistry following core-shell ionization of chemically inequivalent carbon atoms in acetaldehyde (ethanal)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics. Univ Gothenburg, Dept Phys, Origovagen 6B, SE-41296 Gothenburg, Sweden..
Univ Gothenburg, Dept Phys, Origovagen 6B, SE-41296 Gothenburg, Sweden.;Univ Oxford, Dept Chem, Phys & Theoret Chem Lab, S Parks Rd, Oxford OX1 3QZ, England..
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics. Univ Gothenburg, Dept Phys, Origovagen 6B, SE-41296 Gothenburg, Sweden..
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Molecular and condensed matter physics.
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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.

Place, publisher, year, edition, pages
2016.
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-301121OAI: oai:DiVA.org:uu-301121DiVA: diva2:953680
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
In thesis
1. Single-photon multiple ionisation of atoms and molecules investigated by coincidence spectroscopy: Site-specific effects in acetaldehyde and carbon dioxide
Open this publication in new window or tab >>Single-photon multiple ionisation of atoms and molecules investigated by coincidence spectroscopy: Site-specific effects in acetaldehyde and carbon dioxide
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
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:nbn:se:uu:diva-301128 (URN)978-91-554-9665-4 (ISBN)
Public defence
2016-09-30, Polhemssalen, Ångstömlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
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Supervisors
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Byte av lokal vid disputation till Polhemssalen.

Available from: 2016-09-09 Created: 2016-08-18 Last updated: 2016-09-27

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