手性分子2, 3-丁二醇的旋光拉曼光谱研究

本文从拉曼峰和旋光拉曼峰出发,通过键极化率和微分键极化率分析研究(2R, 3R)-2, 3-丁二醇. 通过分子C₁和C₂两种点群的优化结构,获得不依赖于这两种结构的结果 和有关这个手性系统物理图像的丰富信息.对分子拉曼键极化率分析,得出在拉曼弛豫过程中, 电荷主要从外围流向骨架结构.对分子微分键极化率的分析,显示在不对称C原子和与其相联系的H原子 两侧化学键, C-O和C-CH₃的微分键极化率的符号正好相反,意味着这个分子具有相当好的手性 不对称性质.对比对称和反对称的键极化率、微分键极化率,本文得到这样的结论: 对于(特别是键伸缩的)键极化率,(大体上是)对称的大于反对称的; 而对于微分键极化率则是反对称的大于对称的. 关键词： 旋光拉曼 键极化率 微分键极化率 2,3-丁二醇     

(R)-1,3丁二醇的手性不对称性：微分键极化率的研究

本文从(R)-(-)-1,3-丁二醇 ((R)-(-)-1,3-Butanediol) 的拉曼峰强和拉曼旋光峰强, 求得其键极化率和微分键极化率, 得出在拉曼过程中, 电荷主要沿H16 (或H15) O6C3C2C1O5所形成的 (六边) 环向外围的OH键和CH 键流动. 而此环内外化学键的微分键极化率的符号正好相反, 此意味着这个分子具有相当好的手性不对称性质. 关键词： 旋光拉曼 键极化率 微分键极化率 1,3-丁二醇     

Raman excitation of (+)‐(R)‐methyloxirane and its origin of optical activity via bond polarizabilities

We studied the bond polarizabilities of chiral (+)‐(R)‐methyloxirane from its Raman intensities. The bond polarizabilities provide much information concerning the electronic structure of its nonresonant Raman‐excited virtual state. At the initial moment of Raman excitation by the 514.5 nm laser, the tendency of the excited charges (mapped out by the bond polarizabilities) is to spread to the methine bond near the stereogenic center and its triangular oxirane skeleton. Thereby, the coupling of the electric dipole induced by the excited charges in the methine bond and the magnetic moment vibrationally induced by the electric current in the triangular oxirane skeleton as the molecule vibrates is shown to be the key factor leading to its significant Raman chirality. When the final stage of Raman relaxation is approached, the relative magnitudes of the bond polarizabilities are congruent to the bond electronic densities of the ground state, which are otherwise by the theoretical quantities via the quantum chemical calculation. During Raman relaxation, we found that the polarizabilities of the peripheral C H bonds relax faster than the rest, as indicated by their relaxation characteristic times. Copyright © 2010 John Wiley & Sons, Ltd.     

手性分子反-2,3-环氧丁烷的旋光拉曼光谱研究

本文从拉曼峰强出发,求得了反-2,3-环氧丁烷分子的拉曼键极化率,明确了拉曼激发下电荷的分布的信息.还从旋光拉曼(Raman optical activity,ROA)谱的峰强,求取了该分子的旋光拉曼键极化率.由分子手性中心的C-H产生的偶极矩与拉曼激发过程中,电荷流动产生的跃迁磁偶极矩的耦合,来理解旋光拉曼活性产生的机理.分析表明,旋光拉曼活性分子手性中心的C-H键两侧的旋光拉曼极化率符号相反,显示着手性分子局域的不对称性.还得到了对称和反对称坐标的键极化率和旋光拉曼极化率,并且从对称性的角度,即C2群的不可约表示,讨论了这些极化率的内涵.     

Defects in crystals studied by Raman scattering

Raman studies of crystal defects are reviewed. Raman spectroscopy is a powerful technique and has been used widely for investigating disordered structures. The degree of disorder in a crystal is quantitatively evaluated in terms of the phonon correlation length. The asymmetric Raman line shapes in defective crystals such as microcrystals, ion-implanted semiconductors are well reproduced by the spatial correlation (SC) model. The effect of alloying induced-potential fluctuations on Raman scattering is also explained within the framework of the SC model. In disordered graphite, the in-plane phonon correlation length is obtained from the relative intensity ratio of the disorder induced peak. The initial lattice disordering rates and the relaxation rates of disorder are determined, using real-time Raman measurements during ion irradiation in a scale of seconds. In this way, the phonon confinement due to the local defects is observed in the kinetic manner. Localized vibrational modes of defects in crystals are also described. In particular, Raman observation of the hydrogen molecule in crystalline semiconductors is discussed in detail.     

Charge disturbance/excitation in the Raman virtual state revealed by ROA signal: A case study of pinane

The Raman mode intensities are used to extract the bond polarizabilities which are the indication of the charge disturbance/excitation of the Raman virtual state. A classical formula based on the electric and magnetic dipolar coupling among the charges on the atoms is developed which relates the charges and vibrational amplitudes of the atoms in a normal mode to the Raman optical activity(ROA) mode signatures. By fitting with the experimental ROA signatures, we are able to elucidate the scaling parameter which relates the bond polarizability to the electric charge. The result shows that around40% of the charges in pinane are involved in the Raman process under 532 nm laser excitation.     

亚乙基硫脲分子键伸缩模式与全耦合模式键极化率的对比及其拉曼激发虚态的相关研究

从拉曼峰强着手,得到了键伸缩模式与全耦合模式两种不同计算条件下,亚乙基硫脲(ethylene thiourea,ETU)分子的键极化率,并比较分析了两种计算结果的异同.研究表明:在键伸缩模式的算法中,仅考虑势能分布中键对称伸缩比重相对较大的部分拉曼峰参与极化率计算,显然忽略了键伸缩与键弯曲间的相互耦合,造成了与弯曲振动耦合较强的部分键伸缩极化率值存在一定误差.因此,此方法虽能使问题简化,但却丢失了一些信息.而全耦合模式算法考虑了所有振动模式(键伸缩与键弯曲)相互影响的情况,能更全面的反映键电荷的分布情况,但却会使问题的求解过程变得复杂.同时,在拉曼激发虚态的相关研究中,两种计算方法却得到几乎一致的键极化率弛豫方式(呈单指数规律衰减)及相同的衰减特征时间.     

哒嗪分子表面增强拉曼效应下键极化率的研究:吸附构型与增强机理

本文用拉曼峰强求得时间分辨键极化率的方法,分析了哒嗪分子在银电极上的表面增强拉曼谱图.哒嗪分子在不同电位下的键极化率和其弛豫特征时间,显示该分子的吸附点为两个氮原子,以及该分子体系的电荷转移机制机理,包括共轭的效应.对于具有良好拉曼谱图的体系,这个方法具有普适性. 关键词： 哒嗪 拉曼峰强 时间分辨键极化率 弛豫特征时间     

Hydrogen bonding in homochiral dimers of hydroxyesters studied by Raman optical activity spectroscopy

Spectroscopic analysis of homochiral dimerization is important for the understanding of the homochirality of life and enantioselective catalysis. In this paper, (S)‐methyl lactate and related molecules were studied to provide detailed structural information on hydrogen bonding in homochiral dimers of chiral α‐hydroxyesters through the experimental and theoretical study of Raman optical activity. Different homochiral dimers can be distinguished by comparing their simulated Raman optical activity spectra with the experimental results. Hydrogen bonding motions are decoded with the aid of vibrational motion analysis, which are apparently involved in vibrational motions below 800 cm^–1. A common feature related to the chain‐bending mode also indicates the absolute configuration of methyl lactate and related molecules. The differing behavior of electric dipole–electric quadrupole invariants (β(A)²) compared with the electric dipole–magnetic dipole invariant (β(G′)²), suggests that the intermolecular hydrogen bonding motion behaves differently from the intramolecular one in the asymmetric molecular electric and magnetic fields. These results may help understand hydrogen‐bonded self‐recognition and other dynamical features in chiral recognition. Copyright © 2011 John Wiley & Sons, Ltd.     

手性物质拉曼光活性(Raman Optical Activity)研究综述

通过对大量文献的调研，本文分四个部分对手性物质的旋光现象及振动光活性进行了较为全面的介绍，重点介绍了拉曼光活性ＲＯＡ（ＲａｍａｎＯｐｔｉｃａｌＡｃｔｉｖｉｔｙ）产生机理、研究状况及对其研究的意义。     

The relaxations of temporal bond polarizabilities of methylviologen adsorbed on the Ag electrode by 514.5 nm excitation: a Raman intensity study

An algorithm to elucidate the temporal bond polarizabilities from the surface enhanced Raman (SERS) intensities was employed to the case of methylviologen (MV) adsorbed on the Ag electrode. This enables us to obtain the properties of its SERS mechanisms and the effect of its adsorption. The analysis shows that the charge transfer and electromagnetic mechanisms involving in this MV SERS system possess different relaxation times for its various temporal bond polarizabilities. The physics is that the process involved in the charge transfer mechanism will take longer time than that involved in the electromagnetic mechanism since it needs more time to redistribute the charges during relaxation. The time division between these two mechanisms is figured out to be around 3 ps for this system. Adsorption also enhances the relaxation of the temporal bond polarizabilities, in general. The adsorption effect is indicated by the temporal bond polarizabilities close to the final stage of relaxation. They are, in fact, the quantities parallel to the bond electronic densities in the molecular orbital (MO) concept. For comparison, the case of MV solid was also analyzed. Copyright © 2008 John Wiley & Sons, Ltd.     

亚乙基硫脲的表面增强拉曼极化率研究：电磁和电荷转移机制

测量了吸附在银电极表面的亚乙基硫脲分子在不同电位下的表面增强拉曼光谱，对光谱强度变化进行了分析.从拉曼光谱强度计算出分子的键极化率数值，分析极化率大小和变化情况，提出了分子在不同电位下表面增强效应的增强机制. 关键词： 亚乙基硫脲 表面增强拉曼极化率 电磁增强 电荷转移增强     

A novel Raman optical activity instrument operating in the deep ultraviolet spectral region

Raman optical activity (ROA) has been exclusively observed in the visible (VIS) and near‐infrared (NIR) spectral regions to date. During the last few years, we have designed, constructed and tested the first ROA instrument, operating in the deep‐ultraviolet (DUV) spectral region employing 244‐nm excitation. This novel DUV ROA instrument is based on a backscattering geometry and incident circular polarization modulation (ICP); it makes use of a fast DUV imaging lens‐based spectrograph and specially designed DUV grade polarization optics. The performance of this instrument has been evaluated by analysing measured non‐resonant DUV ROA spectra of non‐absorbing enantiomeric liquid samples and by comparing these with corresponding ROA spectra recorded in the visible spectral region. Copyright © 2015 John Wiley & Sons, Ltd.     

咔唑分子拉曼激发虚态的相关研究

根据键极化率与拉曼峰强之间的关系,得到咔唑分子拉曼激发虚态随时间演化的键极化率. 将得到的键极化率的末态与用密度泛函理论得到的基态键电荷密度进行了对比,讨论并分析了拉曼激发虚态键极化率随时间弛豫的特征. 研究表明:咔唑分子在拉曼激发初态时,电子由两个骨架六元环向连通两六元环的连通键上流动,而并非向外围的C–H键上流动. 拉曼激发末态键极化率分布趋势与基态键电荷密度分布很相似,说明激发的电子又流回到分子骨架,即弛豫到基态. 通过对拉曼激发虚态键极化率弛豫过程特征时间的研究,发现连通两六元环的C–C键以及靠近连通键的C–C键的键极化率的弛豫时间较其他键的极化率弛豫时间都长,进一步说明了拉曼激发虚态电子弛豫特征. 这些结果反映了咔唑这类具有连通键的多元环分子在拉曼激发虚态所具有的特征与性质,这对拉曼激发虚态的研究有重要意义. 关键词： 拉曼峰强 键极化率 拉曼激发虚态     

Effect of Environmental Cations on Force Constants,Vibrational Mean Amplitudes and Bond Order of Metaloxygen Bonds in Some Octahedral Oxyanions

The general valenoe force field (GVFF), modified orbital valence force field (MOVFF), and modified Urey-Bradley force field (MUBFF) have been employed to calculate the force constants of octahedral Te⁶⁺o₆, and Ti⁴⁺o₆ anions in the presence of different environmental cations. The mean amplitudes and generalized mean square amplitudes of vibrations for these anions at temperatures; O°K,298. 16°K, and 500°K have also been calculated. Further, the metaloxygen bond order was estimated with the help of general valence stretching force constants. The effects of environmental cations on the force constants, mean amplitudes and π-bonding of metal-oxygen bonds have been critically discussed. The effect of atomic masses of anions on the ooriolis coupling constants of ‘f_iu species has also been outlined.     

甲基紫分子拉曼激发虚态的研究

从拉曼峰强入手,求得了甲基紫分子的“时间分辨键极化率”,并与第一原理计算的基态电子密度做对比,讨论了该分子的激发拉曼虚态的性质.研究结果表明,该分子的拉曼激发虚态中电子向分子外围以及两环之间的键流动,并且拉曼弛豫后的键极化率分布与基态电子的密度分布相似.通过研究键极化率的弛豫过程,发现连接两环的键上的键极化率弛豫时间较其他键大.这些结果说明了甲基紫这类双环分子拉曼激发虚态的性质,这对于研究拉曼散射的中间态具有一定意义. 关键词： 拉曼峰强 时间分辨键极化率 弛豫特征时间     

Temporal electronic structure of non-resonant Raman excited virtual state of P-nitroaniline by 514 nm excitation via bond polarisabilities

We have studied the temporal bond polarisabilities of para-nitroaniline from the Raman intensities by the algorithm proposed by Wu et al.in 1987 (Tian B,Wu G,Liu G 1987 J.Chem.Phys.87 7300).The bond polarisabilities provide much information concerning the electronic structure of the non-resonant Raman excited virtual state.At the initial moment by the 514.5 nm excitation,the tendency of the excited electrons (mapped out by the bond polarisabilities) is to spread to the molecular periphery,and the electronic structure of the Raman virtual state is close to the pseudo-quinonoidic state.When the final stage of relaxation is approached,the bond polarisabilities of those peripheral bonds relax faster than those closer to the molecular core,the phenyl ring.The molecule is in the benzenoidic form as demonstrated by the bond polarisabilities after relaxation.     

Phase transitions in PbZr0.72Sn0.28O3 single crystals studied by Raman spectroscopy

ABSTRACT

Raman light scattering measurements in the temperature range from 80 to 830 K were performed on a PbZr_0.72Sn_0.28O₃ single crystal. The frequencies of the Raman lines were analyzed and discussed in terms of the sequence of structural phase transitions. It was found that Raman spectrum displays important changes near 440, 480 and 493 K. The incorporation of more than 25 mol% of Sn⁴⁺ ions into the structure of PbZrO₃ enhances polar fluctuations above T_C as compared to the less Sn-doped crystals. These fluctuations lead to appearance of a ferroelastic intermediate phase below T_C. It is demonstrated that the structural phase transformation in PbZr_0.72Sn_0.28O₃ can be considered as the result of softening of a number of modes.     

One‐phonon resonant electron Raman scattering in a cylindrical GaAs/AlAs quantum dot

We have presented a theoretical calculation of the differential cross section for the electron Raman scattering process associated with the interface optical phonon modes in cylindrical GaAs quantum dots (QDs) with a AlAs matrix. We consider the Fröhlich electron–phonon interaction in the framework of the dielectric continuum approach. The selection rules for the processes are studied. Singularities are found to be sensitively size‐dependent, and, by varying the size of the QDs, it is possible to control the frequency shift in the Raman spectra. A discussion of the phonon behavior for QDs with different size is presented. Copyright © 2013 John Wiley & Sons, Ltd.     

Tobacco alkaloids analyzed by Raman spectroscopy and DFT calculations

The tobacco alkaloids: nicotine, nornicotine, cotinine, anabasine, their protonated forms, and salts were analyzed by means of Raman spectroscopy supported by the density functional theory/B3LYP/aug‐cc‐pVDZ calculations. The analyses were performed based on Raman marker bands of neutral, monoprotonated, and diprotonated forms of tobacco alkaloids because in different surroundings various forms have been suggested to either dominate or to coexist. The form and distribution of nicotine directly in a plant and in phytopharmaceutical products were investigated by in situ Raman mapping. For the first time, the Raman optical activity spectrum of (−)‐nicotine in aqueous solution was measured and interpreted by means of the density functional theory calculations. The study provides a clear evidence that Raman spectroscopy techniques are powerful in efficient quality control and forensic and bioanalytical analyses of tobacco alkaloids. Copyright © 2012 John Wiley & Sons, Ltd.