荧光材料Y_2O_3:Eu变温拉曼光谱分析

本文用显微拉曼谱仪在波长为785 nm的激光激发下,对Y2O3:Eu陶瓷在温度83-473 K间进行了系统的变温拉曼实验研究。实验发现Y2O3:Eu的一些振动模在低温下没有出现,只有当温度达到一定值之后才可以被观察到,分析表明这是由于温度变化引起的简并振动模式分裂。此外,Y2O3:Eu的拉曼峰位、半高全峰宽(FWHM)也是温度的非线性函数,且不同的拉曼峰遵循不同的函数关系,本文分析这是由于晶格的各向异性导致的。     

Localized vibrational,edges and breathing modes of graphene nanoribbons with topological line defects

Peculiar vibrational modes of graphene nanoribbons (GNRs) with topological line defects were presented. We find that phonon dispersion relations of the topological defective GNRs are more similar to those of perfect armchair-edge GNR than to zigzag-edge GNR in spite of their zigzag edge. All vibrational modes at Γ point are assigned in detail by analyzing their eigenvectors and are presented by video. Three types of characteristic vibrational modes, namely, localized vibrational modes in defect sites, edges, and breathing modes, are observed. Five localized vibrational modes near the defect sites are found to be robust against the width of the topological line-defective GNR. The Raman D’ band just originates from one localized mode, 1622 cm^-1. The vibrational mode is sensitive to symmetry. The edge modes are related with structural symmetry but not with widths. Two edge modes are asymmetrical and only one is symmetrical. The breathing modes are inversely proportional to the width for wide-defect GNRs, and inversely proportional to the square root of the width for narrow-defect GNRs. The breathing mode frequencies of defective GNRs are slightly higher than those of perfect GNRs. These vibrational modes may be useful in the manipulation of thermal conductance and implementation of single phonon storage.     

Solving chemical classification problems using polarized Raman data

When solving chemical classification problems, multivariate analysis has proven to be an important mathematical tool. Unpolarized spectroscopic data, IR, NIR, and UV‐Visible absorption data and unpolarized vibrational Raman data, are typically analyzed by two‐way chemometric methods, e.g. principal component analysis (PCA). When the unpolarized spectra of the different molecules are almost identical, the PCA results in low recognition ratios or even fails. In contrast to absorption processes, Raman scattering can provide polarized data. It is shown, by using mathematical simulations, that the outcome of the PCA can be improved considerably by using the polarized, vibrational Raman data instead of the unpolarized data. The improvement stems from the increased amount of molecular information, which is now available for the PCA of the vibrational data, because the polarization properties of the scattering, expressed through the depolarization ratio (DPR), is very sensitive to small changes in distinct molecular properties and insensitive to sample and experimental variations. For molecules possessing some symmetry, a change of the DPR may be induced by a decrease in symmetry and for highly symmetric molecules non‐dispersive Raman modes typically become dispersive. For dispersive modes, a wavenumber‐dependant change of the DPR may also result from a small energy shift of an allowed electronic transition. We show that the increased information content inherently present in the polarized data, opens up new possibilities for combining the solution of classification problems with an unveiling of details of the different properties and processes in bio‐physic due to various perturbations and changes of the structure of the bio‐molecules. It is also demonstrated that the increased access to molecular information enables in vitro detection of molecular changes often encountered when analyzing biological functions, which are reflected in changes in the excited electronic states. Copyright © 2010 John Wiley & Sons, Ltd.     

Collective vibrational modes in strong electrolyte solutions at high concentrations

We report evidence for the existence of solute related collective vibrational modes in strong II-I electrolyte solutions at high concentrations both in H₂O and D₂O. The evidence was obtained by studying the polarized Raman spectra of solutions of CdCl₂ and NiCl₂ Checks were also performed by taking the Raman spectra of the relative hydrated salts. Our results are explained in terms of vibrational densities of states corresponding to collective vibrational modes in a solute connected middle range lattice.     

Isotropic Raman spectra of liquid (isotope) mixtures: Intermolecular coupling of vibrational modes

The theory presented in this paper investigates the isotropic Raman spectra of liquid binary mixtures. It is found that the collective vibrational modes of different molecular species can be significantly coupled. This is a consequence of the (nearly) resonant vibrational transfer processes, which give rise to distinct vibrational correlations (i.e. correlations between adjacent molecules). The coupling, however, occurs only with weakly-separated or overlapping bands. The more general results of the theory are applied to isotope mixtures. The spectral information available from relevant dilution experiments is interpreted. In particular it is shown that the spectral properties of the vibrational self-correlation part can be concluded from the observed collective correlation function. The significance of the distinct vibrational correlations with respect to the infrared and depolarized Raman spectra is discussed.     

Comparison of Raman spectra and vibrational density of states between graphene nanoribbons with different edges

Vibrational properties of graphene nanoribbons are examined with density functional based tight-binding method and non-resonant bond polarization theory. We show that the recently discovered reconstructed zigzag edge can be identified from the emergence of high-energy vibrational mode due to strong triple bonds at the edges. This mode is visible also in the Raman spectrum. Total vibrational density of states of the reconstructed zigzag edge is observed to resemble the vibrational density of states of armchair, rather than zigzag, graphene nanoribbon. Edge-related vibrational states increase in energy which corroborates increased rigidity of the reconstructed zigzag edge.     

BaBPO5晶体晶格振动光谱研究与第一性原理计算

通过偏振拉曼光谱和第一性原理计算对非线性光学晶体BaBPO₅的 晶格振动模式进行了研究. 实验得到了不同几何配置下、在100–1600 cm^-1范围内的晶体偏振拉曼光 谱与傅里叶变换红外吸收谱, 结合因子群分析方法研究了晶体的外振动与内振动模式特征. 分析表明拉曼振动主要来自于PO₄四面体和BO₄四面体的振动, 且PO₄基团振动具有较强的拉曼与红外活性. 此外,根据第一性原理对晶体拉曼振动进行了数值模拟, 进一步明确了拉曼峰与晶体中原子振动的对应关系, 计算表明拉曼光谱中位于672 cm^-1峰位来自晶体中B–O–P键的伸缩振动, 这是晶体中PO₄四面体和BO₄四面体共顶点连接的特征结构在光谱中的体现.     

三种Schiff碱的Raman振动特性及其归属

本文研究了三种反对称Schiff碱的Raman振动特性,分析了三种Schiff碱的拉曼振动模式,给出了所观察到的Raman振动的归属。     

银杏内酯分子结构和光谱性质的理论研究

采用密度泛函理论方法详细考察四种银杏内酯分子(银杏内酯A、B、C和J)的结构和光谱性质.研究发现，改变银杏内酯上的取代基，银杏内酯分子骨架具有相对稳定的结构.基于优化得到的稳定结构，我们计算得到了四种银杏内酯分子的红外(Infrared,IR)光谱、拉曼(Raman)光谱和振动圆二色(Vibrational circular dichroism,VCD)光谱性质.我们发现，四种银杏内酯分子的IR光谱图在1100 cm-1有较明显的区别，这些振动峰主要是银杏内酯分子中C-O-C键的伸缩振动峰.在Raman光谱图中，波长在3600cm-1处为银杏内酯分子中羟基的伸缩振动，银杏内酯A、银杏内酯B、银杏内酯C分裂成了两个强度不等的振动峰，而银杏内酯J分子表现为一个宽的振动峰.在VCD光谱图中，我们发现四种银杏内酯分子在3800 cm-1附近有明显的区别.     

The Raman and infrared spectra of vitreous BeF2

We report the polarized Raman spectra, the infrared reflectivity and the infrared dielectric constant of vitreous BeF₂, for vibrational frequencies up to 1500 cm^-1. The high frequency modes of the Raman spectrum are assigned to combination overtones as well as to transverse and longitudinal fundamental vibrations.     

一种测量吸附分子列向的方法——利用近阈结构谱和选择定则

局域分子轨道不易受环境影响,因此当分子被吸附且未被破坏时,跃迁到局域分子轨道产生的近阈结构谱基本不受环境影响.对于固定列向的吸附分子,当用偏振X射线测量其近阈结构谱时,相对强度将与偏振方向和分子列向有关.根据这一特性,基于选择定则可以判断吸附分子的列向. 关键词： 量子数亏损理论 近阈结构 选择定则 分子列向     

Vibrational spectra of a GaS single crystal

The Raman and infrared active long wavelength phonons of a GaS single crystal were studied at different temperatures in the 10–600 cm^?1 range. Properly polarized Raman spectra could be obtained with the 4880 Å exciting line and the previous assignment of the E_1g modes controversed recently could be confirmed. Infrared spectra were recorded in the 30–600 cm^?1 region. The vibrational frequencies of the crystal were also calculated using a method developed by Wieting and six new frequencies corresponding to infrared and Raman inactive modes have been proposed.We have observed that the degree of leakage of scattered intensity in unallowed polarizations increases when the wavelength of the exciting line moves off the exciton absorption front. The phonon at 74 cm^?1 was particularly sensitive and the question of the antiresonant behaviour of this compound is raised.     

吡拉西坦和3-羟基苯甲酸药物共晶体及其形成过程的光谱特性分析

药物共晶可以改善药物活性成分的物理化学性质,这一特性使其在改善药物性质特征方面具有很大的应用潜力。本文采用固体研磨的方法制备由吡拉西坦(Piracetam)和3-羟基苯甲酸(3-Hydroxybenzoic acid, 3HBA)作为原料药的药物共晶体,应用傅里叶变换红外(FTIR)、拉曼(Raman)和太赫兹(THz)光谱方法对研磨获得的共晶样品进行表征,并对两原料药和共晶体的分子振动模式进行归属。FTIR,Raman和THz光谱均表明共晶体的振动模式与原料药有着显著的区别。另外,使用Raman和THz光谱技术深入分析共晶体形成的动态过程,实验结果表明在研磨的最初几分钟反应迅速,之后共晶体形成的反应速率变得缓慢,在研磨35 min之后,共晶体的形成过程结束。这一结果为药学领域中有关药物共晶形成的实时监控及其定量分析提供了理论依据和一种有效的技术方法。     

Spectroscopy of phonon and vibronic states of YbAl3(BO3)4 single crystal

The polarized Raman and reflection spectra of a single crystal YbAl₃(BO₃)₄ at room temperature were studied. Raman active vibrational modes A ₁, E _TO, and E _LO are identified. In the Raman spectrum, we detected an intense line at a frequency of 1018 cm⁻¹, which refers to internal vibrations of the BO₃ group and is known to be promising for use in amplifiers based on stimulated Raman scattering. From the simulation of reflection spectra by the method of dispersion analysis the frequencies of A ₂ vibrational modes were determined. Intense bands observed in the low-temperature transmission spectra in the range of f-f transitions in the Yb³⁺ ion are attributed to electron-phonon transitions. The Raman lines are compared with electron-phonon lines in the transmission spectrum.     

Can Raman spectroscopy detect cumulenic structures of linear carbon chains?

The molecular and vibrational structures of cumulenic carbon chains are investigated by density functional theory calculations and compared with that of hydrogen‐capped polyynes. The small value of bond length alternation (BLA) along the CC bonds sequence obtained by geometry optimization of uncapped C_n chains and vinyl‐capped carbon chains confirms their cumulenic structure. It is demonstrated that for finite length chains the structural parameters are determined by end effects as far as the Peierls distortion, expected for very long molecules, does not occur. The Raman spectra of such molecules are calculated to verify the possibility of identifying markers of cumulenic chains by means of vibrational spectroscopy. As expected, the longitudinal mode consisting of the BLA oscillation, which is responsible for the strongest Raman transition of polyynes, becomes very weak for cumulenes; this behaviour is rationalized in terms of local polarizability derivatives. However, other longitudinal modes can be observed in the Raman spectra of C_n chains. The wavenumber behaviour and the optical activity of these modes are interpreted on the basis of the phonon dispersion branch of an ideally infinite cumulenic polymer. Raman intensities computed for chains of different lengths allow to conclude that cumulenic molecules could be detected and identified by means of Raman spectroscopy. Copyright © 2009 John Wiley & Sons, Ltd.     

Metastable carbon allotropes in picosecond-laser-modified diamond

In this paper, we report on the bulk modifications of type IIa single-crystal diamond with visible 10-ps pulses (at λ = 532 nm) and microstructural changes characterized by the appearance of several ‘unidentifiable’ vibrational modes in the frequency range of 1000–1400 cm^?1 in the Raman spectra of laser-modified diamond. It is found that the new Raman modes are strongly pronounced in the spectra of high-stress regions in immediate proximity to the bulk microstructures in the absence of the G mode at ~1580 cm^?1 characteristic of the sp² phase. The high internal stresses are determined from the splitting of the triply degenerate diamond Raman line. The revealed structure transformation is localized within a narrow bulk layer near the bulk microstructures formed, and the stress relaxation is found to result in disappearance of the detected vibrational modes in the spectra. It is suggested that the formation of bulk regions with a sp³ carbon structure consisting of Z-carbon and hexagonal diamond is responsible for the appearance of new Raman modes in the spectra of laser-modified diamond. These findings evidence that the stress-assisted formation of novel metastable carbon phases or defect structures occur in the course of bulk modification of diamond with ps-laser pulses. In addition, we report the results of simulations of internal stresses in the system ‘graphitized cylinder-in-diamond’ to show (1) the effect of the mechanical properties of laser-modified diamond on the resulting stresses and (2) formation of bulk microscopic regions with high stresses of >10 GPa, i.e., the conditions at which various sp³ carbon allotropes and defect structures become more stable than graphite.     

Angular tuning of defect modes spectrum in the one-dimensional photonic crystal with liquid-crystal layer

A one-dimensional ZrO₂/SiO₂ photonic crystal with a 4-n -pentyl-4' -cyanobiphenyl (5CB) nematic defect layer was used to investigate the transmission spectra of light polarized parallel and perpendicular to the liquid-crystal director at different angles of incidence. The spectra of the photonic crystal were shown to split into four polarized components T_ij at oblique incidence. When the incident angle increased, the bandgap edges and the defect modes shifted towards short wavelengths, while the amplitudes of the defect modes increased for the transverse magnetic polarization and decreased for the transverse electric polarization. The observed discrepancy between the defect mode amplitudes in the center and near the edges of the photonic bandgap was found to be related to the radiation losses inside the defect layer of a non-ideal photonic crystal. The simulated transmission spectra obtained using recurrence relations and taking into account the decay of defect modes are in good agreement with the experimental data.     

Investigation of hydrogen bonding in neat dimethyl sulfoxide and binary mixture (dimethyl sulfoxide + water) by concentration-dependent Raman study and ab initio calculation

In this study,our vibrational spectroscopic analysis is made on hydrogen-bonding between dimethyl sulfoxide and water comprises both experimental Raman spectra and ab initio calculations on structures of various dimethyl sulfoxide/water clusters with increasing water content.The Raman peak position of the v(S=O) stretching mode of dimethyl sulfoxide serves as a probe for monitoring the degree of hydrogen-bonding between dimethyl sulfoxide and water.In addition,the two vibrational modes,namely,the CH 3 symmetric stretching mode and the CH 3 asymmetric stretching mode have been analysed under different concentrations.We relate the computational results to the experimental vibrational wavenumber trends that are observed in our concentration-dependent Raman study.The combination of experimental Raman data with ab initio calculation leads to a better knowledge of the nature of the hydrogen bonding and the structures of the hydrogen-bonded complexes studied.     

Bismuth-content-dependent polarized Raman spectrum of InPBi alloy

We systematically investigate the optical properties of the InP_(1-x)Bi_x ternary alloys with 0≤x≤2.46%,by using high resolution polarized Raman scattering measurement.Both InP-like and InBi-like optical vibration modes(LO) are identified in all the samples,suggesting that most of the Bi-atoms are incorporated into the lattice sites to substitute Patoms.And the intensity of the InBi-like Raman mode is positively proportional to the Bi-content.Linear red-shift of the InP-like longitudinal optical vibration mode is observed to be 1.1 cm~(-1)/Bi%,while that of the InP-like optical vibration overtone(2LO) is nearly doubled.In addition,through comparing the(XX) and Z(XY) Raman spectra,longitudinaloptical-plasmon-coupled(LOPC) modes are identified in all the samples,and their intensities are found to be proportional to the electron concentrations.     

4-N-甲基苯乙烯砒啶盐衍生物振动超极化率的理论研究

在双谐振子近似下，利用耦合微扰Hartree-Fock方法计算了4-N-甲基苯乙烯砒啶盐衍生物分子的静态振动第一超极化率和红外与拉曼光谱，给出了对静态振动第一超极化率起主导贡献的两种简正振动模式. 研究发现，标题分子的静态振动第一超极化率都比较大，且与静态电子第一超极化率呈较好的线性关系. 首次提出了利用红外与拉曼光谱特征峰标识的振动模来估算振动第一超极化率大小的少模方法. 结果表明，少模方法用于估算振动第一超极化率的大小是可行的.