排序方式: 共有52条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Verkerk U Fujita M Dzwiniel TL McDonald R Stryker JM 《Journal of the American Chemical Society》2002,124(34):9988-9989
A topologically unique, conformationally constrained tetradentate ligand system for polymetallic coordination chemistry has been developed: tetrakis(2-hydroxyphenyl)ethene (1a) and substituted derivatives. The design exploits the planarity of the tetraphenylethylene core to impart rigidity to the roughly square oxygen binding array, while maintaining a degree of conformational mobility associated with rotation about the aryl-ethylene carbon-carbon bonds. Tetrakis(2-hydroxyphenyl)ethene derivatives are designed to promote multiple metal bridging over chelating coordination modes. The ligand is synthesized from anisole or 4-tert-butylanisole in four steps via the 2,2'-dimethoxybenzophenone hydrazones 4a,b. The sterically hindered ortho-substituted tetraphenylethylene core is produced in high yield by acid-catalyzed decomposition of the corresponding diaryl diazomethane prepared in situ by oxidation of the hydrazone using nickel peroxide. Deprotection of the methyl ethers using boron tribromide gives tetrakis(2-hydroxyphenyl)ethene (1a), characterized by X-ray crystallography, and tetrakis(5-tert-butyl-2-hydroxyphenyl)ethene (1b). Sterically isolating substituents in the 3-position can be installed via Claisen rearrangement/hydrogenation, providing tetrakis(3-n-propyl-2-hydroxyphenyl)ethene (6) efficiently. To illustrate potential applications of this unprecedented ligand class, two coordination complexes are reported, including tetrakis(2-diethylaluminoxyphenyl)ethene (8), a structurally robust eight-membered-ring aluminum/oxygen crown complex characterized both in solution and in the solid state. 相似文献
5.
C. Mennerat-Robilliard L. Guidoni K.I. Petsas P. Verkerk J.-Y. Courtois G. Grynberg 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(1):33-45
All the bright optical lattices studied so far have been designed to obtain a circularly polarized light at the bottom of
the optical potential wells. This condition minimizes the departure rate of the atoms from the fundamental adiabatic surface
and permits an oscillating regime in a large range of parameters. We present here an experimental study of cesium atoms in
a three-dimensional optical lattice, where the light is linearly polarized at the bottom of the potential wells. Temperature
measurements and pump-probe spectroscopy give similar results for this lattice and for the conventional lin lin lattice (which have circular polarizations at the bottom of the wells) despite the fact that one lattice operates in
the jumping regime and the other in the oscillating regime. We study the behaviour of the two types of lattices in a longitudinal
magnetic field, with particular emphasis on the zero field and strong field regimes. The strong field situation is very simple
because the eigenstates are then almost pure Zeeman substates and the adiabatic and diabatic potential surfaces are identical.
The comparison between the zero-field and the high-field situations shows that the diabatic potentials are more appropriate
to account for experimental observations in the novel lattice.
Received: 9 October 1997 / Accepted: 6 November 1997 相似文献
6.
7.
We have investigated nearly degenerate four-wave mixing in neon on the 607 nm line. We have considered the case where one pump beam saturates the medium while the two other incident beams have a much weaker intensity. The frequency of the most intense pump beam is equal to the frequency of the probe beam. When the frequency of the second pump beam is scanned, narrow resonances are observed. These resonances correspond to transitions between the energy levels of the atom dressed by the photons of the intense pump beam. 相似文献
8.
A dressed atom approach of saturation in degenerate four-wave mixing is presented. Because of the Doppler-shift of the pump and probes waves frequencies, a resonance between levels of the dressed atom occurs for two velocity groups. When the Rabi frequency Ω1 is smaller than the Doppler width ku, these resonant terms give the essential contribution to the signal which is analytically calculated. When Ω1 å ku, the signal is expected to be much smaller. 相似文献
9.
Summary We have investigated, experimentally and theoretically, the occurrence of stochastic resonance (SR) in a laser with saturable
absorber: a non-linear optical system presenting optical bistability and self-pulsed regimes for the laser output intensity.
In the optical-bistability regime we have obtained an excellent demonstration of SR by studying Fourier spectra and residence
time distributions; operating just below the Hopf bifurcation that originates pulsed periodic regime we have obtained experimental
evidence of the SR phenomenon. For operation close to the Hopf bifurcation, the theoretical analysis (performed through numerical
simulations) has demonstrated that simultaneous presence of noise and periodic forcing generates excursions far from equilibrium;
from the locking between these excursions and periodic forcing the SR phenomenon may arise.
Paper presented at the International Workshop “Fluctuations in Physics and Biology: Stochastic Resonance, Signal Processing
and Related Phenomena”, Elba, 5–10 June 1994. 相似文献
10.
S.A. van der Aart P. Verkerk W. van der Lugt R. Xu F. van der Horst R.L. McGreevy 《Physica B: Condensed Matter》1997,240(4):311-321
Neutron diffraction measurements on liquid KT1 alloys with 0, 1, and 5 at % Pd, respectively, show that the prepeak in the structure factor shifts from wave vector k=8.0 to 7.2 nm−1 with an increasing amount of Pd. This corresponds to a periodicity change from 0.96 to 1.07 nm in real space2. The structure of the liquid KT1 alloys is compared to the corresponding crystal structures, and some similarities are observed. Reverse Monte Carlo modelling indicates T1 clustering in the liquid alloy. Also in solid KTl Tl-clusters occur. The distance between the clusters increases with the addition of 5%. Pd. More information is needed to discriminate between various possible structures of the Tl clusters in the liquid alloy and to determine the position of Pd in these clusters. 相似文献