| 1. |
- Holland, D. M. P., et al.
(författare)
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A study of the valence shell electronic structure of the 5-halouracils
- 2008
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 352:1-3, s. 205-216
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Tidskriftsartikel (refereegranskat)abstract
- Valence shell photoelectron spectra of the 5-halouracils have been recorded using synchrotron radiation at photon energies of 40 and 80 eV. Photoelectron angular distributions have been determined and these provide an experimental means of deducing the extent to which the molecular orbitals possess predominantly sigma, pi or halogen np character. In chloro-, bromo- and iodouracil two peaks, associated with the essentially halogen atom lone-pair orbitals, have been observed. The separation between these peaks, and the value of their photoelectron asymmetry parameters at an excitation energy of 40 eV, are compared with results for the corresponding orbitals in the halobenzenes and halothiophenes. Vertical ionisation energies and spectral intensities have been evaluated using the many-body Green's function approach, thereby enabling theoretical spectra to be derived. Assignments have been proposed for most of the structure observed in the valence shell photoelectron spectra based upon the available experimental and theoretical evidence.
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| 2. |
- Holland, D. M. P., et al.
(författare)
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A study of the valence shell electronic structure of uracil and the methyluracils
- 2008
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Ingår i: Chemical Physics. - : Elsevier BV. - 0301-0104 .- 1873-4421. ; 353:1-3, s. 47-58
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Tidskriftsartikel (refereegranskat)abstract
- The valence shell photoelectron spectra of uracil, 1-methyluracil and 6-methyluracil have been studied experimentally and theoretically. Synchrotron radiation has been used to record spectra at photon energies of 40 and 80 eV. Photoelectron angular distributions have been determined and these provide an experimental means of distinguishing between sigma- and pi-type orbitals. Vertical ionization energies and spectral intensities have been evaluated using the many-body Green's function approach, thereby enabling theoretical photoelectron spectra to be derived. The calculated spectra display a satisfactory agreement with the experimental data and this has allowed most of the photoelectron bands to be assigned. Two of the outer-valence vertical ionization energies are similar to one another and the vibrational progressions associated with these transitions overlap strongly. Vibronic interaction between these states, induced through the excitation of out-of-plane vibrational modes, may lead to nonadiabatic effects. Preliminary theoretical investigation of this interaction has been performed.
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| 3. |
- Holland, D. M. P., et al.
(författare)
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An experimental and theoretical study of the valence shell photoelectron spectrum of bromochlorofluoromethane
- 2010
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 43:13, s. 135101-
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Tidskriftsartikel (refereegranskat)abstract
- The complete valence shell photoelectron spectrum of bromochlorofluoromethane (CHFClBr), covering the binding energy range similar to 10-50 eV, has been recorded using synchrotron radiation and the observed structure has been interpreted using ionization energies and relative spectral intensities computed using the third-order algebraic-diagrammatic-construction (ADC(3)) scheme for the one-particle Green's function and the outer valence Green's function (OVGF) method. The theoretical results demonstrate that the inner valence region of the photoelectron spectrum is dominated by satellite structure. Angle-resolved photoelectron spectra, recorded at selected excitation energies, have enabled the orbital assignments for the outer valence bands to be confirmed. The four outermost photoelectron bands, ascribed to the two pairs of orbitals associated with the nominally chlorine and bromine lone-pairs, exhibit characteristic angular distributions. The photon energy dependent variations in the relative photoelectron band intensities provide additional support for the orbital assignments.
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| 4. |
- Powis, I., et al.
(författare)
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A study of the valence shell electronic structure and photoionization dynamics of selenophene
- 2007
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 40:11, s. 2019-2041
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Tidskriftsartikel (refereegranskat)abstract
- The photoelectron spectrum of selenophene has been recorded using synchrotron radiation in the photon energy range 20-80 eV and the inner valence region has been studied in detail for the first time. Green's function methods have been employed to evaluate the energies and spectral intensities of all valence shell ionization transitions and the results have facilitated an interpretation of the experimental spectra. Strong configuration interaction results in a redistribution of the intensity associated with the low lying pi(1)( 1b(1)) orbital amongst several satellite states located in the outer valence region. The continuum multiple scattering approach has been used to calculate photoelectron asymmetry parameters for selenophene, thiophene and hydrogen sulphide, and these theoretical predictions have been compared with the corresponding experimental data to assess the influence of Cooper minima and shape resonances. The comparison indicates that the Se 4p and the S 3p Cooper minima have little effect on the valence shell photoionization dynamics of selenophene and thiophene, respectively. This outcome is discussed in connection with the closely related hydrogen selenide and hydrogen sulphide molecules where strong resonant phenomena are observed.
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