| 1. |
- Alagia, M., et al.
(författare)
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Probing the potential energy surface by highresolution x-ray absorption spectroscopy : The umbrella motion of the coreexcited CH3 free radical
- 2007
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Ingår i: Physical Review. A. - 1050-2947 .- 1094-1622. ; 76:2, s. 124305-
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Tidskriftsartikel (refereegranskat)abstract
- A detailed study of the umbrellalike vibration in inner-shell spectroscopy is presented. The high-resolution x-ray absorption spectrum for the lowest lying core excitation of the CH3 free radical was recorded. High quality potential energy surfaces (PES) for the initial and final states of the transition were calculated as a function of the symmetrical stretching and the umbrella deformation coordinates. The strong anharmonicity along the umbrella coordinate in the double-well region of the PES of the core excited state has a strong effect on the bending vibrational progressions. The excellent agreement between the experiment and theory allows an accurate spectroscopic characterization of the vibrational structure of the electronic transition, and the estimation of the umbrella inversion time of 149 fs.
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| 2. |
- Boström, Mathias, et al.
(författare)
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Atomic resonance interaction in dielectric media
- 2004
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 69:5 B, s. 054701-1
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Tidskriftsartikel (refereegranskat)abstract
- The retarded resonance interaction in dielectric media between a ground state atom and an excited atom were investigated. The whole system was represented by a superposition of states:symmetric and antisymmetric with respect to interchange of atoms. While the antisymmetric state can be long lived, the asymmetric state is likely to decay into two ground state atoms. The retarded limit large deviations were demonstrated.
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| 3. |
- Boström, Mathias, et al.
(författare)
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Casimir-Lifshitz interaction between ZnO and SiO2 nanorods in bromobenzene turns repulsive at intermediate separations due to retardation effects
- 2012
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 85:4, s. 044702-
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Tidskriftsartikel (refereegranskat)abstract
- We consider the interaction between a ZnO nanorod and a SiO2 nanorod in bromobenzene. Using optical data for the interacting objects and ambient we calculate the force (from short-range attractive van der Waals force to intermediate-range repulsive Casimir-Lifshitz force to long-range entropically driven attraction). The nonretarded van der Waals interaction is attractive at all separations. We demonstrate a retardation-driven repulsion at intermediate separations. At short separations (in the nonretarded limit) and at large separations (in the classical limit) the interaction is attractive. These effects can be understood from an analysis of multiple crossings of the dielectric functions of the three media as functions of imaginary frequencies.
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| 4. |
- Boström, Mathias, et al.
(författare)
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Comment on "Calculation of the Casimir force between imperfectly conducting plates"
- 2000
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 61:4
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In a recent paper [Phys. Rev. A 59, R3149 (1999)] Lamoreaux reported calculations of the Casimir force. The experimentally found permittivity was used in the calculations. Large deviations were found between numerically evaluated forces and forces derived from a series expanded plasma model. We would like to comment on a few results presented in this work. First, we claim that important features of the imaginary component of the permittivity of copper, presented in Fig. 1(a) are due to the interpolation procedure and are not caused by physical phenomena. These features influence the calculated permittivity for imaginary frequencies, which is the quantity used to calculate the Casimir attraction. Second, we discuss the extrapolation procedure used for low frequencies. The results depend substantially on how this extrapolation is performed.
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| 5. |
- Boström, Mathias, et al.
(författare)
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Enlarged molecules from excited atoms in nanochannels
- 2012
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 86:1, s. 014701-
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Tidskriftsartikel (refereegranskat)abstract
- The resonance interaction that takes place in planar nanochannels between pairs of excited-state atoms is explored. We consider interactions in channels of silica, zinc oxide, and gold. The nanosized channels induce a dramatically different interaction from that in free space. Illustrative calculations for two lithium and cesium atoms demonstrate that there is a short-range repulsion followed by long-range attraction. The binding energy is strongest near the surfaces. The size of the enlarged molecule is biggest at the center of the cavity and increases with channel width. Since the interaction is generic, we predict that enlarged molecules are formed in porous structures, and that the molecule size depends on the size of the nanochannels.
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| 6. |
- Boström, Mathias, et al.
(författare)
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Repulsive van der Waals forces due to hydrogen exposure on bilayer graphene
- 2012
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 85:1, s. 012508-
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Tidskriftsartikel (refereegranskat)abstract
- We consider the effect of atomic hydrogen exposure to a system of two undoped sheets of graphene grown near a silica surface (the first adsorbed to the surface and the second freestanding near the surface). In the absence of atomic hydrogen, the van der Waals force between the sheets is attractive at all separations, causing the sheets to come closer together. However, with the addition of atomic hydrogen between the sheets, the long-range van der Waals interaction turns repulsive at a critical concentration. The underlying triple layer structure (SiO(2)-atomic hydrogen gas-air) gives rise to a long-range repulsion that at large-enough separations dominates over the more rapidly decaying attraction between the two-dimensional undoped graphene sheets (and between the outer graphene sheet and SiO(2)). This may be an avenue to tune the separation between two graphene sheets with the gas concentration. The doping of the graphene layers increases the attractive part of the interaction and hence reduces the net repulsive interaction.
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| 7. |
- Boström, Mathias, et al.
(författare)
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Resonance interaction induced by metal surfaces catalyzes atom-pair breakage
- 2013
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 87:4, s. 044701-
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Tidskriftsartikel (refereegranskat)abstract
- We present the theory for retarded resonance interaction between two identical atoms at arbitrary positions near a metal surface. The dipole-dipole resonance interaction force that binds isotropically excited atom pairs together in free space may turn repulsive close to an ideal (totally reflecting) metal surface. On the other hand, close to an infinitely permeable surface it may turn more attractive. We illustrate numerically how the dipole-dipole resonance interaction between two oxygen atoms near a metal surface may provide a repulsive energy of the same order of magnitude as the ground-state binding energy of an oxygen molecule. As a complement we also present results from density-functional theory.
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| 8. |
- Boström, Mathias, et al.
(författare)
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Retardation turns the van der Waals attraction into a Casimir repulsion as close as 3 nm
- 2012
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 85:1, s. 010701-
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Tidskriftsartikel (refereegranskat)abstract
- Casimir forces between surfaces immersed in bromobenzene have recently been measured by Munday et al. [Nature (London) 454, 07610 (2009)]. Attractive Casimir forces were found between gold surfaces. The forces were repulsive between gold and silica surfaces. We show the repulsion is due to retardation effects. The van der Waals interaction is attractive at all separations. The retardation-driven repulsion sets in at around 3 nm. To our knowledge, retardation effects have never been found at such a small distance before. Retardation effects are usually associated with large distances.
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| 9. |
- Boström, Mathias, et al.
(författare)
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Sign of the Casimir-Polder interaction between atoms and oil-water interfaces: Subtle dependence on dielectric properties
- 2012
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - : American Physical Society. - 1050-2947 .- 1094-1622. ; 85:6, s. 064501-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate that Casimir-Polder energies between noble gas atoms (dissolved in water) and oil-water interfaces are highly surface specific. Both repulsion (e.g., hexane) and attraction (e.g., glycerine and cyclodecane) is found with different oils. For several intermediate oils (e.g., hexadecane, decane, and cyclohexane) both attraction and repulsion can be found in the same system. Near these oil-water interfaces the interaction is repulsive in the nonretarded limit and turns attractive at larger distances as retardation becomes important. These highly surface specific interactions may have a role to play in biological systems where the surface may be more or less accessible to dissolved atoms.
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| 10. |
- Boström, Mathias, et al.
(författare)
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van der Waals energy of an atom in the proximity of thin metal films
- 2000
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 61:5, s. art. no.-052703
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Tidskriftsartikel (refereegranskat)abstract
- The van der Waals energy of a ground-state atom (or molecule) placed between two metal films is calculated at finite temperature. The attraction between thin metal films and a polarizable object can have half-integer separation dependence. This is in contrast to the usual integer separation dependence, shown for instance in the attraction between an atom and a solid surface. We examine how film thickness, retardation, and temperature influence the interaction. To illustrate the effect of finite thickness of the metal film we calculated the van der Waals energy of ground-state hydrogen and helium atoms, and hydrogen molecules, between thin silver films. We finally, briefly, discuss the possibility to measure this effect.
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