排序方式: 共有61条查询结果,搜索用时 15 毫秒
1.
α,β-Unsaturated nitriles can be hydrogenated with enantioselectivities up to 88% ee using chiral ruthenium-diphenylphosphino bisaryl and bisheteroaryl complexes such as ruthenium(II)-BINAP and ruthenium(II)-BINP. Mechanistic investigations indicate that conversion is accelerated by electron-rich ligands and that an additional coordinative group needs be present in order to promote conversion. The chiral products are useful building blocks for the synthesis of histamine H2 agonists of the arpromidine type. 相似文献
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Franzén J Marigo M Fielenbach D Wabnitz TC Kjaersgaard A Jørgensen KA 《Journal of the American Chemical Society》2005,127(51):18296-18304
The development of a general organocatalyst for the alpha-functionalization of aldehydes, via an enamine intermediate, is presented. Based on optically active alpha,alpha-diarylprolinol silyl ethers, the scope and applications of this catalyst for the stereogenic formation of C-C, C-N, C-F, C-Br, and C-S bonds are outlined. The reactions all proceed in good to high yields and with excellent enantioselectivities. Furthermore, we will present mechanistic insight into the reaction course applying nonlinear effect studies, kinetic resolution, and computational investigations leading to an understanding of the properties of the alpha,alpha-diarylprolinol silyl ether catalysts. 相似文献
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Johnsson P López-Martens R Kazamias S Mauritsson J Valentin C Remetter T Varjú K Gaarde MB Mairesse Y Wabnitz H Salières P Balcou P Schafer KJ L'Huillier A 《Physical review letters》2005,95(1):013001
We use a train of sub-200 attosecond extreme ultraviolet (XUV) pulses with energies just above the ionization threshold in argon to create a train of temporally localized electron wave packets. We study the energy transfer from a strong infrared (IR) laser field to the ionized electrons as a function of the delay between the XUV and IR fields. When the wave packets are born at the zero crossings of the IR field, a significant amount of energy (approximately 20 eV) is transferred from the field to the electrons. This results in dramatically enhanced above-threshold ionization in conditions where the IR field alone does not induce any significant ionization. Because both the energy and duration of the wave packets can be varied independently of the IR laser, they are valuable tools for studying and controlling strong-field processes. 相似文献
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Antonio Degasperis Matteo Conforti Fabio Baronio Stefan Wabnitz Sara Lombardo 《Letters in Mathematical Physics》2011,96(1-3):367-403
The spectral theory of the integrable partial differential equations which model the resonant interaction of three waves is considered with the purpose of numerically solving the direct spectral problem for both vanishing and non vanishing boundary values. Methods of computing both the continuum spectrum data and the discrete spectrum eigenvalues are given together with examples of such computations. The explicit spectral representation of the Manley-Rowe invariants is also displayed. 相似文献
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N. V. Vysotina N. N. Rozanov V. E. Semenov S. V. Fedorov S. Wabnitz 《Optics and Spectroscopy》2006,101(5):736-742
Sets of steady-state localized temporal structures of radiation with a duration comparable with the period corresponding to the frequency of atomic transitions are found for a medium consisting of active (with a pump) and passive (without a pump) atoms with homogeneous broadening. The velocity of motion of these structures takes discrete values depending on the number of field spikes and the number of oscillations of the polarization of the active and passive atoms within the intervals between the field spikes. 相似文献
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H. Wabnitz Y. Mairesse L. J. Frasinski M. Stankiewicz W. Boutu P. Breger P. Johnsson H. Merdji P. Monchicourt P. Salières K. Varjú M. Vitteau B. Carré 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(2):305-311
We investigate the carrier-envelope phase dependence of the total ionization yield for single and double ionization of xenon.
We compare our results to theoretical calculations and to the phase dependent asymmetry in photoelectron emission. We observe
that the phase dependence of the photoion yields, regardless if single or double ionization, is at least 2-3 orders of magnitude
below the photoelectron emission signal. We conclude that total photoionization yields are only very weakly dependent on the
carrier envelope phase, and that they are not a useful means for measurement of the phase. It seems possible that the broad
bandwidth of few-cycle pulses facilitates multiphoton ionization, which leads to a randomization of strong field ionization
phase dependencies. Besides, we observe that the spatial asymmetry in photoelectron emission appears to be useful as an indicator
for the laser pulse duration in the few cycle regime. 相似文献
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We analyze the control of the propagation speed of three wave packets interacting in a medium with quadratic nonlinearity and dispersion. We find analytical expressions for mutually trapped pulses with a common velocity in the form of a three-parameter family of solutions of the three-wave resonant interaction. The stability of these novel parametric solitons is simply related to the value of their common group velocity. 相似文献
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Lossless polarizers are conservative nonlinear optical devices that transform unpolarized light into highly polarized light without polarization-dependent losses. The device proposed here consists of an up to 100-m-long segment of nonlinear highly birefringent or unidirectionally spun fiber pumped from the output end by an intense backward-propagating beam. An initially unpolarized (scrambled) signal beam acquires a degree of polarization close to 100% toward the fiber output. 相似文献