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Core-shell photoabsorption and photoelectron spectra of gas-phase pentacene: Experiment and theory
ISMN-CNR, Rom.
Università di Roma "La Sapienza" .
Università di Roma "La Sapienza" .
Università di Modena e Reggio Emilia.
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2005 (English)In: Journal of chemical physics Online, ISSN 1089-7690, Vol. 122, no 12, 124305- p.Article in journal (Refereed) Published
Abstract [en]

The C K-edge photoabsorption and 1s core-level photoemission of pentacene (C22H14) free molecules are experimentally measured, and calculated by self-consistent-field and static-exchange approximation ab initio methods. Six nonequivalent C atoms present in the molecule contribute to the C 1s photoemission spectrum. The complex near-edge structures of the carbon K-edge absorption spectrum present two main groups of discrete transitions between 283 and 288  eV photon energy, due to absorption to * virtual orbitals, and broader structures at higher energy, involving * virtual orbitals. The sharp absorption structures to the * empty orbitals lay well below the thresholds for the C 1s ionizations, caused by strong excitonic and localization effects. We can definitely explain the C K-edge absorption spectrum as due to both final (virtual) and initial (core) orbital effects, mainly involving excitations to the two lowest-unoccupied molecular orbitals of * symmetry, from the six chemically shifted C 1s core orbitals. ©2005 American Institute of Physics

Place, publisher, year, edition, pages
2005. Vol. 122, no 12, 124305- p.
Keyword
organic compounds, photoexcitation, photoelectron spectra, SCF calculations, ab initio calculations, chemical shift, molecular electronic states, molecule-photon collisions
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-12685DOI: 10.1063/1.1864852OAI: oai:DiVA.org:liu-12685DiVA: diva2:16859
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2013-11-25
In thesis
1. Time-dependent molecular properties in the optical and x-ray regions
Open this publication in new window or tab >>Time-dependent molecular properties in the optical and x-ray regions
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Time-dependent molecular properties are important for the experimental characterization of molecular materials. We show how these properties can be calculated, for optical and x-ray frequencies, using novel quantum chemical methods. For xray absorption there are important relativistic effects appearing, due to the high velocity electrons near the atomic nuclei. These effects are treated rigorously within the four-component static exchange approximation. We also show how electron correlation can be taken into account in the calculation of x-ray absorption spectra, in time-dependent density functional theory based on the complex polarization propagator approach. The methods developed have been applied to systems of experimental interest|molecules in the gas phase and adsorbed on metal surfaces. The effects of molecular vibrations have been take into account both within and beyond the harmonic approximation.

Place, publisher, year, edition, pages
Institutionen för fysik, kemi och biologi, 2007
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1131
Keyword
Quantum chemistry, molecular physics, x-ray spectroscopy, relativity
National Category
Other Physics Topics
Identifiers
urn:nbn:se:liu:diva-10125 (URN)978-91-85895-88-5 (ISBN)
Public defence
2007-10-23, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2007-10-30 Created: 2007-10-30 Last updated: 2009-04-26
2. Birefringences and X-ray absorption from relativistic and nonrelativistic quantum chemical methods
Open this publication in new window or tab >>Birefringences and X-ray absorption from relativistic and nonrelativistic quantum chemical methods
2005 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Application of quantum chemical methods for the prediction and interpretation of optical and X-ray experiments have been performed. X-ray absorption and X-ray photo-electron spectroscopy of pentacene in the gas phase has been studied using the static exchange approximation. A generalizat ion of the static exchange approximation, to the relativistic four-component realm is presented and applied to the H2S molecule. This generalization allows for a description of the effects the strong spin-orbit coupling in the core region of atoms. Two types of birefringences, Faraday effect and electric field gradient induced birefringence, a re calculated for small molecules in the gas phase, and the effects of relativity are considered for these nonlinear optical properties.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2005. 40 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1211
Series
LIU-TEK-LIC, 66
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-31976 (URN)17818 (Local ID)91-8545-772-8 (ISBN)17818 (Archive number)17818 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2013-11-25

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Ekström, Ulf

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