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- Hedin, Lage, et al.
(author)
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N1s and O1s double ionization of the NO and N2O molecules
- 2014
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In: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 140:4, s. 044309-
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
- Hedin, Lage, et al.
(author)
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Single site double core level ionisation of OCS
- 2014
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In: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 439, s. 111-116
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Journal article (peer-reviewed)abstract
- Single site O1s, C1s and S2p double ionisation of the OCS molecule has been investigated using a magnetic bottle multi-electron coincidence time-of-flight spectrometer. Photon energies of 1300, 750 and 520 eV, respectively, were used for the ionisation, and spectra were obtained from which the double core ionisation energies could be determined. The energies measured for 1s double ionisation are 1172 eV (O1s(-2)) and 659 eV (C1s(-2)). For the S2p double ionisation three dicationic states are expected, P-3, D-1 and S-1. The ionisation energies obtained for these states are 373 eV (P-3), 380 eV (D-1) and 388 eV (S-1). The ratio between the double and single core ionisation energies are in all cases equal or close to 2.20. Auger spectra of OCS, associated with the O1s(-2), C1s(-2) and S2p(-2) dicationic states, were also recorded incorporating both electrons emitted as a result of the filling of the two core vacancies. As for other small molecules, the spectra show an atomic-like character with Auger bands located in the range 480-560 eV for oxygen, 235-295 eV for carbon and 100-160 eV for sulphur. The interpretation of the spectra is supported by CASSCF and CASCI calculations. The cross section ratio between double and single core hole creation was estimated as 3.7 x 10(-4) for oxygen at 1300 eV, 3.7 x 10(-4) for carbon at 750 eV and as 2.2 x 10(-3) for sulphur at 520 eV. (C) 2014 Elsevier B.V. All rights reserved.
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- Holland, D. M. P., et al.
(author)
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A study of the valence shell photoionisation dynamics of pyrimidine and pyrazine
- 2011
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In: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 390:1, s. 25-35
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Journal article (peer-reviewed)abstract
- The complete valence shell photoelectron spectra of pyrimidine and pyrazine have been recorded with synchrotron radiation and the observed structure has been interpreted with the aid of vertical ionisation energies and relative spectral intensities calculated using time-dependent density functional theory. The theoretical predictions for the single-hole ionic states due to outer valence shell ionisation agree satisfactorily with the experimental results. Ionisation from the inner valence orbitals is strongly influenced by many-body effects and the intensity associated with a particular orbital is spread amongst numerous satellites. Photoelectron angular distributions and partial cross sections have been determined both experimentally and theoretically, and demonstrate that shape resonances affect the valence shell photoionisation dynamics. In addition to shape resonances occurring a few eV above the ionisation threshold, the calculations indicate that many of the orbitals are influenced by shape resonant processes at much higher energies. Some of these higher energy resonances have been confirmed through a comparison between the relevant theoretical and experimental photoelectron asymmetry parameters. The spectral behaviour of asymmetry parameters associated with pi-orbitals has been shown to differ from that of asymmetry parameters associated with sigma-orbitals. These differences provide a means of distinguishing between the two types of orbitals even in heavily congested regions of the photoelectron spectrum suffering from band overlap.
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- Feifel, Raimund, et al.
(author)
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From localised to delocalised electronic states in free Ar, Kr and Xe clusters
- 2004
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In: European Physical Journal D. Atomic, Molecular, Optical and Plasma Physics. - : Springer Science and Business Media LLC. - 1434-6060 .- 1434-6079. ; 30:3, s. 343-351
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Journal article (peer-reviewed)abstract
- We present new results for the inner valence levels of clusters of the three inert gases Ar, Kr and Xe based on photoelectron spectroscopy studies. The inner valence levels are compared to the localised core levels and to the delocalised outer valence levels. This comparison shows a gradual change from a relatively localised behaviour for Ar inner valence 3s, over the intermediate case of Kr inner valence 4s, to a more delocalised behaviour for Xe inner valence 5s. This change correlates well with the ratio between the orbital sizes and the interatomic distances. The Kr4s intermediate case is found to exhibit characteristics of both localised and delocalised behaviour.
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