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Synchrotron radiation spectroscopy of molecular dynamics beyond the valence shell
KTH, School of Engineering Sciences (SCI), Physics.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents experimental results on molecular spectroscopy of gas phase molecules using synchrotron radiation. It deals mainly with dynamical processes following resonant excitation of electrons from core and inner-valence shells of the following systems H2O, H2, SF6 and CD4. In order to reach these deep electrons and excite them photons in the energy range from 25 to 550 eV were used, depending on the particular system.

Two experimental techniques are used. Photon induced fluorescence spectroscopy is used to study the fluorescence emission of fragments after the decay of resonant coreexcited states for the water molecule, and after doubly excited states and resonant excitations of inner-shell electrons for H2 and SF6 respectively. Only the emission in the visible and near infrared range (300-900nm) and the Lyman-α transitions are measured. Energy resolved electron-ion coincidence is used for the study of the fragmentation of CD4 and SF6 after selective ionisation of one of the outer-valence orbitals. In the case of CD4 the fragmentation is compared for the cases in which the ionisation is done directly, or through participator Auger decay of different resonantly core-excited states.

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , xiv, 59 p.
Series
Trita-FYS, ISSN 0280-316X ; 2006:13
National Category
Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-3899ISBN: 91-7178-294-X (print)OAI: oai:DiVA.org:kth-3899DiVA: diva2:9935
Public defence
2006-04-20, Sal FB 53, AlbaNova, Roslagstullsbacken 21, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100910Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2010-09-10Bibliographically approved
List of papers
1. Fluorescence Emission of Excited Hydrogen Atoms after Core Excitation of Water Vapor
Open this publication in new window or tab >>Fluorescence Emission of Excited Hydrogen Atoms after Core Excitation of Water Vapor
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2006 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Physical review letters, Vol. 96, 063003- p.Article in journal (Refereed) Published
Abstract [en]

The Balmer emission from atomic hydrogen has been recorded across the resonances at the oxygen K edge of the water molecule using synchrotron radiation excitation. The emission is observed to be strongest at excitations to Rydberg resonances. The observations are interpreted using a qualitative model for the dynamics of the core-to-Rydberg excited molecule. The model links the quantum state of the core-excited water molecule via resonant Auger decay and subsequent dissociation to the state of the fluorescing hydrogen atom.

Keyword
Electric excitation, Fluorescence, Mathematical models, Quantum theory, Resonance, Synchrotron radiation
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-5534 (URN)10.1103/PhysRevLett.96.063003 (DOI)000235394100025 ()2-s2.0-33144476336 (Scopus ID)
Note
QC 20100910Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2017-11-21Bibliographically approved
2. Fluorescence emission following core excitations in the water molecule
Open this publication in new window or tab >>Fluorescence emission following core excitations in the water molecule
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2006 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 39, no 5, 1101-1112 p.Article in journal (Refereed) Published
Abstract [en]

Photon-induced fluorescence spectroscopy has been used to study the fragmentation of the water molecule at the O 1s is edge. Fluorescence emission has been observed from the neutral fragments H, O and OH as well as from the ionic fragments O+ and OH+. The extracted fluorescence yields of the H Lyman-alpha emission and O 2p(3)(S-4)3p(P-3) -> 2p(3)(S-4)3s(S-3) transitions show the same structures as the total ion yield spectrum but with different relative intensities. The most intense fluorescence emission is restricted to the region of the core excitations, while above the O 1s ionization limit the signal is much weaker (in the case of H) or below the detection limit (O, OH and OH+). The fluorescence emission is concluded to follow from the following general cascade: the core-excited states decay by resonant Auger transitions, the final states reached undergo dissociation into ionic and neutral fragments, and fluorescence occurs from excited fragments. In the case of the OH (A(2)Sigma(+) -> X-2 Pi) emission, the decay of core-excited states through soft x-ray emission may also be responsible for the observed fluorescence.

Keyword
high-resolution photoabsorption, dispersed spectroscopy, h2o, dissociation, oh, d2o, photodissociation, photofragments, ultraviolet, radicals
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-5535 (URN)10.1088/0953-4075/39/5/009 (DOI)000237753700014 ()2-s2.0-33244473688 (Scopus ID)
Note
QC 20100910Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2017-11-21Bibliographically approved
3. Fluorescence study of doubly excited states of molecular hydrogen
Open this publication in new window or tab >>Fluorescence study of doubly excited states of molecular hydrogen
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2006 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 39, no 2, 205-213 p.Article in journal (Refereed) Published
Abstract [en]

Photodissociation of molecular hydrogen has been investigated by means of fluorescence spectroscopy using synchrotron radiation. Balmer-alpha emission from atomic hydrogen photofragments was collected in the 20-55 eV excitation energy range. Experimental data are interpreted in terms of excitation and fragmentation of neutral doubly excited states and excited ionic states with the aid of recent theoretical model calculation.

Keyword
dissociative photoionization, autoionizing states, h-2, photodissociation, fragments, dynamics, series, h2
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-5536 (URN)10.1088/0953-4075/39/2/001 (DOI)000235457800004 ()2-s2.0-29144513913 (Scopus ID)
Note

QC 20100910

Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2017-11-21Bibliographically approved
4. Synchrotron radiation induced fluorescence spectroscopy of SF6
Open this publication in new window or tab >>Synchrotron radiation induced fluorescence spectroscopy of SF6
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2005 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 38, 387- p.Article in journal (Refereed) Published
Abstract [en]

The fluorescence of gaseous SF6 was investigated after excitation with 25-80eV synchrotron radiation photons. The total UV-Vis-near IR fluorescence yield was recorded and interpreted in terms of inner valence excitations/ionizations and double excitations in SF6. Dispersed fluorescence measurements in the 400-1000 nm spectral range reveal excited S, S+, F and F+ fragments as solely responsible for the emission. The fluorescence intensity of some of the observed atomic transitions was monitored as a function of the excitation energy. Single, double and triple excitations as well as direct ionizations and shake-ups are proposed as the triggering processes responsible for the creation of the emitting fragments.

Keyword
threshold photoelectron-spectroscopy, electron-impact, sulfur-hexafluoride, vacuum-ultraviolet, cross-sections, inner-valence, energy, shell, photoabsorption, fragmentation
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-5537 (URN)10.1088/0953-4075/38/4/006 (DOI)000228249700007 ()2-s2.0-14544275080 (Scopus ID)
Note
QC 20100910Available from: 2006-04-05 Created: 2006-04-05 Last updated: 2017-11-21Bibliographically approved
5. Core-excitation-induced dissociation in CD4 after participator Auger decay
Open this publication in new window or tab >>Core-excitation-induced dissociation in CD4 after participator Auger decay
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2003 (English)In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 68, no 2Article in journal (Refereed) Published
Abstract [en]

The fragmentation of the CD4 molecule after selective ionization of the 1t(2) and 2a(1) electrons with photons from 70 to 290 eV has been studied with the energy-resolved electron-ion coincidence technique. The mass spectra acquired in coincidence with 1t(2) electrons reveal CD4+, CD3+, and CD2+ fragments, depending on the excitation energy used. The production of CD3+ is strongly enhanced after C 1s excitation to different core excited states, with respect to the production observed after direct ionization of the 1t(2) orbital. This enhancement is correlated with the changes of the molecular geometry when it relaxes from the core-excited state.

Keyword
k-shell excitation, electron-ion coincidence, ch4, spectroscopy, molecules, methane, spectrum, impact, photoionization, fragmentation
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-22793 (URN)10.1103/PhysRevA.68.022715 (DOI)000185192100070 ()
Note
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2017-12-12Bibliographically approved
6. An energy resolved electron-ion coincidence study near the S 2p thresholds of the SF6 molecule
Open this publication in new window or tab >>An energy resolved electron-ion coincidence study near the S 2p thresholds of the SF6 molecule
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2003 (English)In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 36, no 4, 781-791 p.Article in journal (Refereed) Published
Abstract [en]

The fragmentation dynamics of the SF6 molecule following the excitations of S 2p electrons into unoccupied molecular orbitals has been studied using the energy-resolved electron-ion coincidence technique. Fragmentation patterns were found to depend on the particular excitation and on the electronic state of the molecular ion. The spectator resonant Auger decay at the 2p --> 6a(1g) resonance induces changes in the ion distributions as compared to direct photoionization. Furthermore, coincidence spectra related to the same Auger structure display different ion abundances at the 2t(2g) and 4e(g) shape resonances. Differences were also found in the Auger decay spectra. These findings give further support for the previously suggested many-electron character of the 4e(g) shape resonance.

Keyword
fragmentation, photoionization, resolution, spectra, states, shell
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-22651 (URN)10.1088/0953-4075/36/4/310 (DOI)000184012300016 ()
Note
QC 20100525Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2017-12-12Bibliographically approved
7. Experimental station for gas phase fluorescence spectroscopy
Open this publication in new window or tab >>Experimental station for gas phase fluorescence spectroscopy
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2004 (English)In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 75, no 7, 2402-2408 p.Article in journal (Refereed) Published
Abstract [en]

The details of an experimental setup for gas phase atomic and molecular fluorescence measurements using synchrotron radiation are described in this article. The most significant part of the apparatus is an optical arrangement, which allows for simultaneous measurements of dispersed as well as total fluorescence intensity using an effusive gas jet and an inbuilt gas cell assembled in a convenient plug and measure configuration. The first measurements concerning fluorescence of the N-2 molecule around the N 1s edge obtained with this setup are presented.

Keyword
dispersed fluorescence, n2 molecule, photoionization, n-2, excitation, resonances, states
National Category
Atom and Molecular Physics and Optics
Identifiers
urn:nbn:se:kth:diva-6869 (URN)10.1063/1.1764605 (DOI)000222847900027 ()2-s2.0-3843064413 (Scopus ID)
Note
QC 20100910Available from: 2004-11-30 Created: 2004-11-30 Last updated: 2010-09-10Bibliographically approved

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