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| 2. |
- Magnuson, Martin, 1965-, et al.
(författare)
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Resonant inelastic soft X-ray scattering spectra at the nitrogen and carbon K-edges of poly(pyridine-2,5-diyl)
- 1999
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - 0368-2048 .- 1873-2526. ; 101-103, s. 573-578
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Tidskriftsartikel (refereegranskat)abstract
- Resonant inelastic scattering measurements of the conjugated polymer, poly(pyridine-2,5-diyl) have been performed at the nitrogen and carbon K-edges using synchrotron radiation. For comparison, molecular orbital calculations of the spectra have been carried out with the repeat unit as a model molecule of the polymer chain. The resonant emission spectra show depletion of the π electron bands which is consistent with symmetry selection and momentum conservation rules. The depletion is most obvious in the resonant inelastic scattering spectra of carbon while the nitrogen spectra are dominated by lone pair n orbital emission of σ symmetry and are less excitation energy dependent. By comparing the measurements to calculations an isomeric dependence of the resonant spectra is found giving preference to two of the four possible isomers in the polymer.
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| 3. |
- Magnuson, Martin, 1965-, et al.
(författare)
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The electronic structure of poly(pyridine-2,5-diyl) investigated by soft X-ray absorption and emission spectroscopies
- 1998
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Ingår i: Chemical Physics. - 0301-0104 .- 1873-4421. ; 237:3, s. 295-304
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of the poly-pyridine conjugated polymer has been investigated by resonant and non-resonant inelastic X-ray scattering and X-ray absorption spectroscopies using synchrotron radiation. The measurements were made for both the carbon and nitrogen contents of the polymer. The analysis of the spectra has been carried out in comparison with molecular orbital calculations taking the repeat-unit cell as a model molecule of the polymer chain. The simulations indicate no significant differences in the absorption and in the non-resonant X-ray scattering spectra for the different isomeric geometries, while some isomeric dependence of the resonant spectra is predicted. The resonant emission spectra show depletion of the electron bands in line with symmetry selection and momentum conservation rules. The effect is most visual for the carbon spectra; the nitrogen spectra are dominated by lone pair n orbital emission of symmetry and are less frequency dependent.
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| 4. |
- Qian, L, et al.
(författare)
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Formation of titanium fulleride studied by x-ray spectroscopies
- 1999
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Ingår i: PHYSICAL REVIEW B-CONDENSED MATTER. - 0163-1829. ; 59:19, s. 12667-12671
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The chemical interaction between titanium and C-60 in coevaporated titanium-fulleride films has been investigated by x-ray photoelectron spectroscopy, (XPS), x-ray absorption spectroscopy (XAS), and x-ray emission spectroscopy. Two titanium-fulleride film
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| 7. |
- Agüero-Torres, H, et al.
(författare)
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Dementia is the major cause of functional dependence in the elderly : 3-year follow-up data from a population-based study
- 1998
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Ingår i: American Journal of Public Health. - : American Public Health Association. - 0090-0036 .- 1541-0048. ; 88:10, s. 1452-1456
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVES: The purpose of this investigation was to study the role of dementia and other common age-related diseases as determinants of dependence in activities of daily living (ADL) in the elderly. METHODS: The study population consisted of 1745 persons, aged 75 years and older, living in a district of Stockholm. They were examined at baseline and after a 3-year follow-up interval. Katz's index was used to measure functional status. Functional dependence at baseline, functional decline, and development of functional dependence at follow-up were examined in relation to sociodemographic characteristics and chronic conditions. RESULTS: At baseline, factors associated with functional dependence were age, dementia, cerebrovascular disease, heart disease, and hip fracture. However, only age and dementia were associated with the development of functional dependence and decline after 3 years. In a similar analysis, including only nondemented subjects. Mini-Mental State Examination scores emerged as one of the strongest determinants. The population attributable risk percentage of dementia in the development of functional dependence was 49%. CONCLUSIONS: In a very old population, dementia and cognitive impairment make the strongest contribution to both the development of long-term functional dependence and decline in function.
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| 10. |
- Cesar, A, et al.
(författare)
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Resonant x-ray scattering beyond the Born-Oppenheimer approximation: Symmetry breaking in the oxygen resonant x-ray emission spectrum of carbon dioxide
- 1997
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Ingår i: Journal of Chemical Physics. - 0021-9606. ; 106:9, s. 3439-3456
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Tidskriftsartikel (refereegranskat)abstract
- Although resonant x-ray scattering of molecules fulfills strict electronic symmetry selection rules, as now firmly proven by. spectra of diatomic molecules, the accumulated body of data for polyatomic molecules indicates that an apparent breaking of these rules represents the common situation rather than the exception. The CO2 molecule provides a good example of symmetry breaking, with the. oxygen x-ray emission spectra showing strong intensity for transitions that are forbidden by the parity selection rule. We present time-independent and time-dependent theories for frequency-dependent resonant x-ray scattering beyond, the Born-Oppenheimer approximation in order to explore under what circumstances one can anticipate symmetry breaking in the spectra of polyatomic molecules. The theory starts out from the Kramers-Heisenberg dispersion relation and is generalized for vibrational degrees of freedom and for nonadiabatic coupling of the electronic (vibronic) states, including the frequency dependency of, the scattering cross section. Different Limiting cases and few-level models are considered. The symmetry breaking is proven to be the result of pseudo-Jahn-Teller-Like vibronic coupling between near-degenerate core-excited states. Thus vibromic interaction over the antisymmetric vibrational mode between the ''bright'' 1 sigma(g)(-1)2 pi(u)(-1) and ''dark'' 1 sigma(u)(-1)2 pi(u)(-1) intermediate states of CO2 allows transitions otherwise forbidden. The measurements and theory demonstrate that the symmetry-selective character of the resonant x-ray emission is strongly frequency dependent. The strong intensity of ''dipole-forbidden'' transitions in the pi* oxygen K spectrum at resonance is reduced monotonically with the detuning of the excitation energy from resonance, and the spectra become ''symmetry purified.'' Simulations with full vibronic coupling predict this feature of the x-ray scattering experiment and a few-level model explains the energy dependence of the symmetry selection and the symmetry purification at large detuning energies in the limit of narrowband photon excitation.
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