11,471 research outputs found
Many-body Rabi oscillations of Rydberg excitation in small mesoscopic samples
We investigate the collective aspects of Rydberg excitation in ultracold
mesoscopic systems. Strong interactions between Rydberg atoms influence the
excitation process and impose correlations between excited atoms. The
manifestations of the collective behavior of Rydberg excitation are the
many-body Rabi oscillations, spatial correlations between atoms as well as the
fluctuations of the number of excited atoms. We study these phenomena in detail
by numerically solving the many-body Schr\"edinger equation.Comment: 8 pages, 5 figure
Assembling an isomer grid: the isomorphous 4-, 3- and 2-fluoro-N'-(4-pyridyl)benzamides
The three title isomers, 4-, (I), 3-, (II), and 2-fluoro-N'-(4-pyridyl)benzamide, (III), all CââHâFNâO, crystallize in the P21/c space group (No. 14) with similar unit-cell parameters and are isomorphous and isostructural at the primary hydrogen-bonding level. An intramolecular C-H...O=C interaction is present in all three isomers [C...O = 2.8681 (17)-2.884 (2) Ă
and C-H...O117-118°], with an additional N-H...F [N...F = 2.7544 (15) Ă
] interaction in (III). Intermolecular amide-pyridine N-H...N hydrogen bonds link molecules into one-dimensional zigzag chains [graph set C(6)] along the [010] direction as the primary hydrogen bond [N...N = 3.022 (2), 3.049 (2) and 3.0213 (17) Ă
]. These are augmented in (I) by C-H...Ï(arene) and cyclic C-F...Ï(arene) contacts about inversion centres, in (II) by C-F...F-C interactions [C...F = 3.037 (2) Ă
] and weaker C-H...Ï(arene)/C-H...F contacts, and in (III) by C-H...Ï(arene) and C=O...O=C interactions, linking the alternating chains into two-dimensional sheets. Typical amide N-H...O=C hydrogen bonds [as C(4) chains] are not present [N...O = 3.438 (2) Ă
in (I), 3.562 (2) Ă
in (II) and 3.7854 (16) Ă
in (III)]; the C=O group is effectively shielded and only participates in weaker interactions/contacts. This series is unusual as the three isomers are isomorphous (having similar unit-cell parameters, packing and alignment), but they differ in their interactions and contacts at the secondary level
2-Ferrocenyl-N-(2-ferrocenylbenzoyl)-N-(4-methyl-2-pyridyl)benzamide
The title compound, [Fe2(C5H5)2(C30H22N2O2)], a 2:1 product of the reaction of 2-ferrocenylbenzoic acid and 2-amino-4-methylpyridine, forms a twisted molecular structure in the solid state due to steric effects from the two benzene rings ortho-substituted with ferrocenyl and carbonyl-derived groups. A short intramolecular C-H...[pi] interaction is observed involving a substituted [eta]5-C5H4 ring and an ortho H atom of the benzene ring on the opposite side of the molecule. In the crystal structure, there are no classical hydrogen bonds: interactions comprise a short C6-H...[pi](C6) interaction involving substituted benzene rings and two C-H...O=C interactions per molecule
Fano Lineshapes Revisited: Symmetric Photoionization Peaks from Pure Continuum Excitation
In a photoionization spectrum in which there is no excitation of the discrete
states, but only the underlying continuum, we have observed resonances which
appear as symmetric peaks, not the commonly expected window resonances.
Furthermore, since the excitation to the unperturbed continuum vanishes, the
cross section expected from Fano's configuration interaction theory is
identically zero. This shortcoming is removed by the explicit introduction of
the phase shifted continuum, which demonstrates that the shape of a resonance,
by itself, provides no information about the relative excitation amplitudes to
the discrete state and the continuum.Comment: 4 pages, 3 figure
Observation of a resonant four-body interaction in cold cesium Rydberg atoms
Cold Rydberg atoms subject to long-range dipole-dipole interactions represent
a particularly interesting system for exploring few-body interactions and
probing the transition from 2-body physics to the many-body regime. In this
work we report the direct observation of a resonant 4-body Rydberg interaction.
We exploit the occurrence of an accidental quasi-coincidence of a 2-body and a
4-body resonant Stark-tuned Forster process in cesium to observe a resonant
energy transfer requiring the simultaneous interaction of at least four
neighboring atoms. These results are relevant for the implementation of quantum
gates with Rydberg atoms and for further studies of many-body physics.Comment: 5 pages, 5 figure
IRAS observations of irregular galaxies
Normal irregular galaxies seem to be unusual in having vigorous star formation yet lacking the many dark nebulae typical of spirals. The Infrared Astronomy Satellite (IRAS) observations of a large sample of irregulars are used to explore the dust contents of these galaxies. Compared to normal spirals, the irregulars generally have higher L sub IR/L sub B ratios, warmer f(100)/f(60) dust color temperatures, and lower globally-averaged dust/gas ratios. The relationship between the infrared data and various global optical properties of the galaxies is discussed
Synthesis, structural and conformational analysis of a 3 x 3 isomer grid based on nine Methyl-N-(pyridyl)benzamides
- âŠ