| 1. |
- Gelmukhanov, F, et al.
(författare)
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Collapse of vibrational structure in spectra of resonant x-ray Raman scattering
- 1997
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 56:1, s. 256-264
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Tidskriftsartikel (refereegranskat)abstract
- Extreme narrowing, or collapse, of electron-vibrational bands is predicted as a new phenomenon in resonant radiative and nonradiative x-ray scattering (RXS) spectra. It is shown that in the inelastic scattering case, that is, when the potential surfaces of ground and final slates are different, a considerable narrowing of the vibronic RXS band results from detuning the excitation Photon frequency omega away from the absorption resonance. By fine tuning the frequency, this may under special circumstances also occur in the region of strong photoabsorption. In the case of elastic Rayleigh scattering, that is, when the potential surfaces of ground and final states are identical, the narrowing results in a total collapse to a single resonance by detuning the frequency. The theory predicts how the differencies in vibrational structure of resonant and nonresonant photoemission spectra depends on the excitation frequency. The effect of frequency detuning on complex spectral multilevel structures due to multiplet: and spin-orbit splittings is discussed qualitatively. It is shown that the notion of: duration time for the x-ray scattering process plays a crucial role in the understanding of RXS spectra.
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| 2. |
- Gel'mukhanov, Faris, et al.
(författare)
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Doppler effects in resonant x-ray Raman scattering
- 1998
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 57:4, s. 2511-2526
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Tidskriftsartikel (refereegranskat)abstract
- Theory for Doppler effects in resonant x-ray Raman scattering (RXS) is presented. It is shown that the "electron" Doppler effect is important in nonradiative RXS for decay transitions between continuum nuclear states lying above the dissociation threshold, and that the averaging of the RXS cross section over molecular orientations can lead to strong non-lorentzian broadenings of the atomiclike resonances. The Doppler effect is found to give a unique possibility to distinguish dissociating identical atoms, because different peaks correspond to atoms with opposite Doppler shifts. Spectral features of the atomiclike profile are predicted and analyzed. Strong oscillations of the RXS cross section will occur as a consequence of the interference of the Auger electrons. Due to the Doppler effect and the interference, the atomiclike profile can be associated with supernarrow spectral features, the width of which goes below the lifetime broadening and is practically independent of the spectral distribution of the incident radiation. As another consequence of the oscillations and strong anisotropy caused by the interference, we predict parity selection rules for Auger decay transitions in both bound and dissociative systems. The corresponding experiments can be realized by measurements of resonant Auger of surface adsorbed molecules and for molecules by the electron-ion coincidence technique.
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| 3. |
- Gel’mukhanov, Faris, et al.
(författare)
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Duration of x-ray Raman scattering
- 1999
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 59:1, s. 380-389
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Tidskriftsartikel (refereegranskat)abstract
- There has recently been much interest in using the notion of a duration time to analyze resonant x-ray Raman scattering (RXS) of atoms, molecules, and solids. This notion implies a selection of processes with different time scales responsible for the formation x-ray Raman spectra, and has been useful for actual predictions of various phenomena associated with RXS and that subsequently have been experimentally verified. However, the notion of a duration time for the x-ray scattering event can also have some paradoxical consequences, as when comparing the RXS duration with the relaxation time of the wave packet evolution in the case when the inverse detuning of the excitation energy is shorter than the time of flight or the lifetime of the core excited state. We present here a solution of this contradiction and give a detailed analysis of the notion of the duration time for RXS. It is shown that this time is complex and consists of two qualitatively different contributions. The first originates in the irreversible decay of the core excited state, while the imaginary part is caused by a reversible dephasing in the time domain. We investigate also the evolution of the wave packets of bound and dissociative states to stationary distributions. The theoretical analysis is accompanied by numerical examples of the time evolution of the wave packet in bound and dissociative core excited states of the N2 and HCl molecules.
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| 4. |
- Henderson, M., et al.
(författare)
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Lifetimes of the 5d ^{9} 6p levels in Hg III
- 1999
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 59:5, s. 4068-4070
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Tidskriftsartikel (refereegranskat)abstract
- We report measurements and theoretical calculations for the lifetimes of the 5d96p levels in Hg iii with J=0,2,3,4. This is an extension of earlier measurements of the lifetimes of the 5d96p levels in Hg iii with J=1, and now provides data for all 12 of the levels. The results also provide an isoelectronic comparison with earlier studies of these levels in Au ii of the Pt sequence, and a homologous comparison with earlier studies of the 4d95p levels in Ag ii, Cd iii, and In iv in the Pd sequence.
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| 5. |
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| 6. |
- Larsson, Jan-Åke, 1969-
(författare)
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Bell’s inequality and detector inefficiency
- 1998
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 57:5, s. 3304-3308
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a method of generalizing the Bell inequality is presented that makes it possible to include detector inefficiency directly in the original Bell inequality. To enable this, the concept of “change of ensemble” will be presented, providing both qualitative and quantitative information on the nature of the “loophole” in the proof of the original Bell inequality. In a local hidden-variable model lacking change of ensemble, the generalized inequality reduces to an inequality that quantum mechanics violates as strongly as the original Bell inequality, irrespective of the level of efficiency of the detectors. A model that contains change of ensemble lowers the violation, and a bound for the level of change is obtained. The derivation of the bound in this paper is not dependent upon any symmetry assumptions such as constant efficiency, or even the assumption of independent errors.
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| 7. |
- Larsson, Jan-Åke, 1969-
(författare)
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Detector efficiency in the Greenberger-Horne-Zeilinger paradox : independent errors
- 1999
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 59:6, s. 4801-4804
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Tidskriftsartikel (refereegranskat)abstract
- The Greenberger-Horne-Zeilinger (GHZ) paradox is subject to the detector-efficiency “loophole” in a similar manner as the Bell inequality. In a paper by J.-Å. Larsson [Phys. Rev. A 57, R3145 (1998)], the issue is investigated for very general assumptions. Here, the assumptions of constant efficiency and independent errors will be imposed, and it will be shown that the necessary and sufficient efficiency bound is not lowered, but remains at 75%. An explicit local-variable model is constructed in this paper to show the necessity of this bound. In other words, it is not possible to use the independence of experimental nondetection errors to rule out local realism in the GHZ paradox below 75% efficiency.
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| 8. |
- Larsson, Jan-Åke, 1969-
(författare)
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Necessary and sufficient detector-efficiency conditions for the Greenberger-Horne-Zeilinger paradox
- 1998
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 57:5, s. R3145-R3149
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Tidskriftsartikel (refereegranskat)abstract
- In this paper detector efficiency conditions are derived for the Greenberger-Horne-Zeilinger (GHZ) paradox. The conditions will be necessary and sufficient, i.e., the GHZ paradox is explicable in terms of a local-variable model if the efficiency is below the bounds, and the GHZ prerequisites are inconsistent at higher efficiencies. The derivation does not make use of any of the symmetry assumptions usually made in the literature, most notably the assumption of independent errors. The errors in local-hidden-variable models are governed by the “hidden variable” and, therefore, one cannot in general assume that the errors are independent. It will be shown that this assumption is not necessary. Moreover, bounds are presented that do not need the emission rate of particle triples to be known. An example of such a bound is the ratio of the triple coincidence rate and the double coincidence rate at two detectors, which needs to be higher than 75% to yield a contradiction.
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| 9. |
- Magnuson, Martin, et al.
(författare)
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Competition between decay and dissociation of core-excited carbonyl sulfide studied by x-ray scattering
- 1999
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 59:6, s. 4281-4287
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Tidskriftsartikel (refereegranskat)abstract
- We show evidence of dissociation during resonant inelastic soft x-ray scattering Carbon and oxygen K-shell and sulfur L-shell resonant and nonresonant x-ray emission spectra were measured using monochromatic synchrotron radiation for excitation and ionization. After sulfur L-2,L-3-->pi*, sigma* excitation, atomic lines are observed in the emission spectra as a consequence of competition between de-excitation and dissociation. In contrast thr carbon and oxygen spectra show weaker line-shape variations and no atomic Lines. The spectra are compared to results from ab initio calculations. The discussion of the dissociation paths is based on calculated potential energy surfaces and atomic transition energies.
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| 10. |
- Ninham, BW, et al.
(författare)
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Lifshitz theory of Casimir forces at finite temperature
- 1998
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 57, s. 1870-1880
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Tidskriftsartikel (refereegranskat)abstract
- We reexamine the Casimir and Lifshitz theories of intermolecular forces at nonzero temperature. For dilute media and atomic interactions, the limits of validity of the London-van der Waals potential between atoms at finite temperature are established by a detailed asymptotic analysis. In the retarded limit, the Casimir-Polder interaction potential is shown to be rigorously correct only in the limit of zero temperature. At any non-zero temperature a different analytic form obtains and is derived. We then consider Casimir forces between perfectly conducting plates. Existing results for the case of intervening vacuum are recovered by a novel method. Moreover, we show that the Mellin transform technique and theory of generalized zeta functions allows a detailed asymptotic treatment of a system of perfectly conducting plates with an intervening electron plasma, useful in the modeling of forces between metal plates, where the finite metallic skin-depth is an important consideration.
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