共查询到20条相似文献,搜索用时 62 毫秒
1.
D.M. Rampulla 《Surface science》2006,600(14):2823-2829
The enantioselective surface chemistry of two chiral alkyl halides, S-1-bromo-2-methylbutane and R-2-bromobutane, have been compared on the naturally chiral Cu(6 4 3)R&S surfaces. Temperature programmed reaction spectroscopy was used to quantify the yields of the various decomposition products during heating. A fraction of the adsorbed alkyl bromides desorb intact while the remainder decomposes by debromination to form either S-2-methyl-1-butyl or R-2-butyl groups on the surfaces. The S-2-methyl-1-butyl group then reacts by β-hydride elimination to form 2-methyl-1-butene or by hydrogenation to form 2-methylbutane. The R-2-butyl group reacts by β-hydride elimination to form butene or by hydrogenation to form butane. This surface chemistry on Cu(6 4 3)R&S is not enantioselective at low coverages but is enantioselective at high coverages. In R-2-bromobutane the chiral carbon atom coincides with the debromination reaction center while the β-hydride elimination centers are achiral. In S-1-bromo-2-methylbutane the chiral carbon atom coincides with the β-hydride elimination reaction center while the center for debromination is achiral. Results show that the enantioselectivities are influenced by the surface structure to a greater extent than they are by the adsorbate structure. 相似文献
2.
本文报道了一个简化的利用可见光和红外光带宽来计算和频光谱分辨率的公式. 公式显示和频振动光谱的Voigt线宽可以通过振动模式的均匀线宽(洛伦兹线宽)、非均匀线宽(高斯线宽)、红外光与可见光的高斯线宽计算获得. 利用本实验室新搭建的频率分辨及偏振分辨的皮秒和频光谱系统验证了该公式的准确性. 实验结果显示,本激光系统获取的红外光的高斯线宽为1.5 cm-1. 本激光系统的光谱分辨率约为4.6 cm-1,结果与胆固醇单层膜光谱获取的光谱分辨率(3.5~5 cm-1)基本一致. 相似文献
3.
4.
The full Landau potential was determined for a
ferroelectric liquid crystal doped with varying concentrations of the chiral dopant R1011 and its enantiomer S1011. A multi-curve
fitting procedure using temperature and electric field dependent tilt angle and polarization data was employed to the generalized
Landau model of ferroelectric liquid
crystals. From this analysis the three Landau coefficients as well as the polarization-tilt coupling parameters were obtained
as a function of dopant concentration and configuration. It is shown that the two most varied
parameters are those of the first Landau coefficient α and the
(chiral) linear polarization-tilt coupling constant C. The effect on the
first Landau term is equivalent for the two dopants of opposite handedness
indicating its achiral nature, while the effect on the (chiral) bilinear
coupling term differs for the R1011 and S1011 dopant, increasing and
decreasing the coupling between tilt and polarization respectively. This
difference in the bilinear coupling term quantifiably evidences that the
R1011 dopant increases and S1011 dopant reduces the inherent chirality in
this system. 相似文献
5.
6.
Guéna J Chauvat D Jacquier P Jahier E Lintz M Sanguinetti S Wasan A Bouchiat MA Papoyan AV Sarkisyan D 《Physical review letters》2003,90(14):143001
We have detected, by using stimulated emission, an atomic parity violation (APV) in the form of a chiral optical gain of a cesium vapor on the 7S-6P(3/2) transition, consecutive to linearly polarized 6S-7S excitation. We demonstrate the validity of this detection method of APV, by presenting a 9% accurate measurement of expected sign and magnitude. We stress several advantages of this new approach which fully exploits the cylindrical symmetry of the setup. Future measurements at the percent level will provide an important cross-check of an existing more precise result obtained by a different method. 相似文献
7.
We demonstrate a self-organizing system that generates patterns by dynamic feedback: two periodic surfaces collectively structure an intervening liquid sandwiched between them, which then reconfigures the original surface features into moiré patterns as it evaporates. Like the conventional moiré phenomenon, the patterns are deterministic and tunable by mismatch angle, yet additional behaviors-chirality from achiral starting motifs and preservation of the patterns after the surfaces are separated-emerge uniquely from the feedback process. Patterning menisci based on this principle provides a simple, scalable approach for making a series of complex, long-range-ordered structures. 相似文献
8.
9.
Fukuda J 《The European physical journal. E, Soft matter》2007,24(1):91-98
It was shown experimentally (P.V. Dolganov et al., Europhys. Lett. 76, 250 (2006)) and by numerical calculations (C. Bohley, R. Stannarius, Eur. Phys. J. E 23, 25 (2007)) that the c -director profile of a two-dimensional chiral smectic-C (SmC) film around a circular inclusion adopts dipolar rather than
quadrupolar configuration observed in achiral SmC films. We give an analytical argument on how spontaneous bend inherent in
chiral SmC liquid crystals influences the configuration of a SmC liquid crystal film around a circular inclusion imposing
tangential anchoring. We find how the angle α between two surface defects seen from the center of the inclusion depends on
the radius of the inclusion R and the strength of the spontaneous bend q . We show, however, that the contribution of the spontaneous bend to the free energy suffers from mathematical ambiguity;
it depends on the mathematical treatment of the outer boundary even when it is at infinity. This might indicate that the shape
as well as the treatment of the outer boundary of the film can significantly influence the equilibrium configuration of the
c -director and the position of the surface defects. 相似文献
10.
Boyko Katranchev 《Phase Transitions》2016,89(2):115-132
Microtextural polarization, phase transitions, and electro-optical effects are studied in a series of nanocomposites, grown by mixing alkyloxybenzoic acids (nOBAs), displaying hydrogen-bonded dimeric liquid crystal (LC) state, with non-mesogens (single-walled carbon nanotubes (SWCNTs), perfluorooctanoic acid) or mesogens (bent-core LC compound D14F3). Each of the studied nanocomposites, in which the nOBA serves as a matrix, forms complexes with bent-shaped dimeric, caused by the interaction between the dopant structural units and the dimer rings. This feature, coordinated with the surface anchoring, bulk and electrical effects, leads to drastic reduction of the LC system symmetry. As a result, transitions from achiral (characteristic for the pristine nOBA) to chiral states (including ferroelectric smectic C with C2 symmetry and ferroelectric smectic CG with the lowest C1 triclinic one) take place. The functionalization of the SWCNTs causes drastic increase of the ferroelectricity. 相似文献
11.
Optical sum-frequency generation (SFG) is used to characterize CO stretching vibrations on Pt(111) and Pt(110) surfaces. Different adsorption sites (terminal, bridge and step sites) are identified in the SFG spectra of CO on Pt(111), in good quantitative agreement with previous infrared reflection-absorption experiments on this system. For CO on Pt(110) we only observe CO molecules on terminal sites. The measured CO stretching vibration frequencies on Pt(110), both for low and high coverages, are at variance with the results of previous infrared studies. Our SFG results for CO on Pt(110) are confirmed by independent EELS measurements which, in addition, also reveal the frustrated rotational mode and the metal-CO vibration. The measured frequency of 2065 cm−1 for low CO coverage on Pt(110)-(1 × 2) is consistent with a previously proposed empirical relation between the frequency of an isolated adsorbed CO molecule and the coordination number of the binding Pt surface atom. 相似文献
12.
Sensing of chiral compounds has gained great attentions for many decades. Chiral nanomaterials with a greater surface area, optical properties, and stability have however not been well realized in this field. Herein, strategies for the preparation of chiral Ag and Au nanomaterials are focused upon, including Ag and Au nanoparticles conjugated with chiral molecules with/without containing fluorophores, chiral nanoassemblies of Ag and Au nanoparticles, and chiral Ag and Au nanoclusters. The chirality of nanomaterials originates from their core and/or ligand, meanwhile that for nanoassemblies results from their complex spatial configuration. An emphasis is given to circular dichroism, colorimetry/UV–vis absorption, and fluorescence detection modes for sensing enantiomers and achiral analytes using the chiral Ag and Au nanomaterials. Several interesting examples for quantitation of DNA, proteins, peptides, drugs, and pollutants are provided to highlight their potential as sensitive and selective nanomaterials for enantiomer recognition and sensing of achiral analytes. Several important issues to be solved when using chiral nanomaterials for chiral recognition are specified. Some strategies for improving the sensitivity and selectivity of chiral nanomaterials for chiral recognition are suggested. The aim is to bring more attention to the potential of chiral nanomaterials for sensing important analytes such as chiral drugs. 相似文献
13.
Using a quantum model for the atom dissipative interactions with metallic surfaces developed earlier [Surface Sci. 117 (1982) 116; 126 (1983) 666], we investigate the effect of the dynamic electronic response of a clean surface on sticking of He in the limit of very low incoming energies. We show within a perturbational approach that the electronic polarization and overlap induced He-surface interactions, although giving rise to a considerable increase of sticking probability in the low energy limit, cannot explain the sticking probabilities of the order of unity observed recently at very low energies [Sinvani et al., Phys. Rev. Letters 51 (1983) 188]. 相似文献
14.
A principle possibility of second harmonic generation (SHG) from the surface of a chiral medium by normally incident focused fundamental beam has been shown earlier, and the key features of this phenomenon (forbidden in a planewave approximation) have been outlined in [N.I. Koroteev, V.A. Makarov, S.N. Volkov, Laser Phys. 8 (1998) 532-535]. In our work we have obtained analytical expressions, which describe the distributions of intensity and polarization in the cross-section of a second-harmonic (SH) light beam. It is found that the polarization state drastically changes along the cross-section of the signal light beam. The polarization effects concerning the transversal inhomogeneous polarization distribution were studied in detail. It is shown that the measurement of the polarization state in certain areas of the SH beam cross-section gives us quantitative information directly about the medium material constants. 相似文献
15.
Cherfi Y Hemine J Douali R Beldjoudi N Ismaili M Leblond JM Legrand C Daoudi A 《The European physical journal. E, Soft matter》2010,33(4):335-342
Linear and non-linear dielectric measurements were carried out on a ferroelectric liquid crystal stabilized by an anisotropic
polymer network. The polymerization process was achieved at room temperature. It was performed from an achiral monomer in
the ferroelectric chiral smectic C phase, exhibiting a very short helical pitch and a large polarization. The linear and non-linear
dielectric spectroscopy were also completed by textural morphology as well as structural and ferroelectric characterizations.
All these measurements were carried out on a pure ferroelectric liquid crystal material and on composite films containing
two polymer concentrations. The increase of the polymer network density leads to a decrease of the dielectric strength determined
in the linear and non-linear dielectric spectroscopy. The complementarity between the linear and non-linear dielectric measurements
and their confrontation with a theoretical model allowed the simultaneous determination of some physical parameters such as
macroscopic polarization, rotational viscosity and twist elastic energy. We also discuss the effect of the polymer network
density on the obtained physical parameters. 相似文献
16.
Zhen Li Huali Liu Fei Li Jiaqi Zhao Yu Wang 《Particle & Particle Systems Characterization》2020,37(3):2000008
The direct synthesis of a chiral nematic liquid crystalline phase of AgNR@SiO2@cysteine@CsPbBr3 hybrid nanorods (HNRs) is reported. The circular dichroism spectra can be divided into three components: (1) the interband absorption–enhanced optical activity of structural arrangement of cysteine (cys) molecules, 200–320 nm, (2) the chiral nematic liquid crystalline arrangement of the Ag nanorods (AgNRs), 350–450 nm, and (3) the exciton adsorption edge of the perovskite, 500–550 nm. The polarizing optical microscope images indicate that the chiroptical response of perovskite arises from chiral nematic crystalline arrangement rather than cys-induced electronic coupling between a chiral ligand and otherwise achiral perovskite quantum dots (QDs). The luminescent intensity of CsPbBr3 QDs in AgNR@SiO2@cys@CsPbBr3 HNRs is boosted 87-fold due to the local surface plasmon resonance field enhancement effect. Furthermore, the high-performance green light emitting diode is constructed employing AgNR@SiO2@cys@CsPbBr3 complexes, which exhibit excellent luminescent properties. This work contributes insights into structure–property relationships and this strategy promisingly provides guidance for the other inorganic chiral semiconductor suprastructures. 相似文献
17.
A macroscopic helical twist is imposed on an achiral nematic liquid crystal by controlling the azimuthal alignment directions at the two substrates. On application of an electric field the director rotates in the substrate plane. This electroclinic effect, which requires the presence of chirality, is strongest at the two substrates and increases with increasing imposed twist distortion. We present a simple model involving a trade-off among bulk elastic energy, surface anchoring energy, and deracemization entropy that suggests the large equilibrium director rotation induces a deracemization of chiral conformations in the molecules-effectively "top-down" chiral induction-quantitatively consistent with experiment. 相似文献
18.
We explore the phase behavior of a rigid achiral bent-core model system. Nematic and smectic phases form at higher densities, whereas micelles and columns composed of chiral clusters of these molecules self-assemble at lower densities. No nucleation mechanism requiring transient chirality is possible in the formation of these chiral superstructures due to the rigid achiral nature of the substituents. We show the chiral micelles are minima of the potential energy surface using energy minimization and parallel tempering simulations. Chiral dopants were found to induce the system to adopt a consistent chiral twist direction, the first molecular scale computer simulation of this effect. 相似文献
19.
矢量辐射传输方程定量描述了辐射在地表-大气耦合介质中的传输过程,是定量遥感的基础.在处理辐射和离散介质相互作用时,如何处理多次散射、辐射偏振效应和耦合地表模型是研究的重点,直接影响定量化遥感反演的精度.文中基于逐次散射近似法求解了矢量辐射传输方程,求解过程中耦合典型地表的非偏双向反射(BRDF)模型和偏振双面反射(BPDF)模型.采用相对误差因子定量分析了地表双向反射效应和大气偏振效应对天基矢量辐射的影响.为进一步研究地表-大气耦合介质系统的偏振特性及地表大气参数的定量遥感反演提供理论支持.
关键词:
矢量辐射传输方程
逐次散射近似
定量遥感
偏振遥感 相似文献
20.
Jianfeng Dong 《Optics Communications》2010,283(4):532-536
Guided and surface modes in the chiral nihility fiber consisting of a chiral nihility metamaterial core with an achiral cladding have been investigated. The dispersion equations of guided and surface modes in the chiral nihility fiber and their cutoff frequencies are derived. Dispersion curves of guided and surface modes are presented and the effect of chirality parameter on dispersion curves is discussed in detail. Some novel propagation characteristics are found. 相似文献