亚乙基硫脲分子激发拉曼虚态的研究

本文从拉曼峰强入手,求得了亚乙基硫脲(ETU)分子的"时间分辨键极化率",并讨论了该分子的激发拉曼虚态性质,发现了该分子"激发虚态电子向分子外围键流动"、"电子弛豫后的键极化率分布与基态电子的密度分布相似"、"不同激发波长下的键极化率衰减时间满足不确定关系"等特点。本文还研究了该分子的表面增强拉曼光谱,指出"电荷转移机制"的极化率弛豫时间长于"电磁增强机制"等与表面增强拉曼效应相关的结论。     

硫脲在酸性溶液中的表面增强拉曼光谱

本文在电镀沉积的银衬底上,研究了硫脲分子在酸性溶液中的表面增强拉曼散射。结果表明,硫脲分子是通过硫原子倾斜着吸附在银表面;当溶液中的ＨＣｌ浓度增加时,在银表面吸附的硫脲分子面更加偏离银表面的法线方向;实验结果还暗示,该体系存在着较强的化学增强机制。     

硫脲在铂电极表面吸附行为的表面增强拉曼光谱研究

本文通过电化学方法有效抑制了硫脲在铂电极表面的解离,从而实现了用SERS技术研究粗糙铂电极表面硫脲的吸附行为。结果表明,硫脲分子是以硫端斜躺吸附在电极表面,随着电位变负渐渐转为直立。     

银溶胶中电荷转移诱导的表面增强拉曼光谱研究

在银溶胶中加入具有双官能团的对氨基苯甲酸分子,银纳米粒子可以通过耦联分子PABA的作用相连,在两个或几个银纳米粒子间形成亚纳米级的间隙,处于间隙中的耦联分子的拉曼信号被极大的增强,尤其是b2振动模式得到了极大增强,这可能是由于银纳米粒子间耦联分子的隧道电荷转移现象引起的.     

钴的表面增强拉曼散射中的电磁增强因子计算

本文初步探讨了钴电极的表面增强拉曼散射机理。采用二维阵列理论模型在 0 .5～ 4.0eV的光子能量范围对钴纳米椭球阵列的表面增强拉曼散射 (SERS)现象进行了理论分析。有关计算表明 ,经过合适的表面粗糙化的钴金属电极能产生较弱的表面增强效应 (SERS增强因子约 1 0 2 ～ 1 0 4 ) ,制备出具有高纵横比的纳米粒子阵列是得到钴体系较大的SERS增强因子的关键     

表面增强拉曼光谱研究聚乙烯咔唑(PVK)在银表面的吸附状况

ＰＶＫ表面增强光谱及粉末拉曼光谱的对比分析表明,ＰＶＫ分子是通过杂五环和邻 双取代苯环同衬底银表面吸附的,且ＰＶＫ分子与银原子之间存在电荷转移。     

时间分辨表面增强拉曼光谱研究银电极表面硫脲和ClO_4~-共吸附层的结构

本文应用时间分辨表面增强拉曼光谱（ＴＲＳＥＲＳ）结合电位阶跃和电位扫描的方法，研究了硫脲和ＣｌＯ－４在Ａｇ电极表面的共吸附层结构。结果表明ＳＥＲＳ谱峰强度随电极电位的响应速率与电位阶跃扫描的方向有关，ＴＵ和ＣｌＯ－４在Ａｇ表面的共吸附层在不同的电位下存在两种不同的构型，并且两种构型之间转化的难易程度不同。     

硫脲吸附在电镀银表面的SERS

研究了在盐酸水溶中硫脲分子的表面增强拉曼散射。实验结果表明：硫脲分子倾斜吸附在银表面。当盐酸浓度增加时,硫脲分子平面更加偏离银表面的法线方向。     

Temporal electronic structures of nonresonant Raman excited virtual states: a case study of ethylene thiourea

An algorithm is employed to elucidate molecular bond polarizabilities of ethylene thiourea including their temporal relaxation from Raman intensities, which provide much information concerning the electronic distribution of nonresonant Raman excited virtual states. The main character of the excited states of ethylene thiourea is that the excited electrons tend to flow to the molecular periphery because of electronic repulsion. It is noted that the bond electronic densities of the ground state can be mapped out by the bond polarizabilities at the final stage of relaxation. The relaxation time is shown to be proportional to the wavelength of the exciting light in agreement with Heisenberg's uncertainty principle, showing that the excitations are indeed not the stationary eigenstates. Copyright © 2007 John Wiley & Sons, Ltd.     

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     

Surface‐enhanced Raman spectra of the neonicotinoid pesticide thiacloprid

Thiacloprid is a widely used pesticide belonging to the neonicotinoid class, which is characterized by a selective activity against insects and a reduced acute toxicity for humans. The importance of the environmental impact of neonicotinoids is being intensively researched, in order to evaluate the danger they pose for useful insects. Physical methods which allow the characterization of neonicotinoids in diluted aqueous solutions are therefore desirable. We present a study of Raman and surface‐enhanced Raman scattering (SERS) spectroscopy on thiacloprid in solid state, in acetone solution, and adsorbed onto silver and gold hydrosols at μM concentration. Density functional theory calculations allow the individualization of the most stable molecular structure, both in gas phase and in solution, and of the corresponding Raman spectra. The vibrational assignments lead to an interpretation of the differences between SERS and ordinary Raman spectra based on the possible interactions between the molecule and the metal surface, the main one involving the iminocyano group. Formation of a charge‐transfer complex is suggested by the dependence of the SERS spectra on the laser excitation wavelength. We evaluate the applicability of SERS spectroscopy to the chemical analysis of thiacloprid comparing SERS with current analytical methods. Copyright © 2013 John Wiley & Sons, Ltd.     

Surface‐enhanced Raman scattering study of Ag@PPy nanoparticles

Surface‐enhanced Raman scattering (SERS) spectra of Ag@polypyrrole (PPy) nanoparticles with both 488 and 1064 nm excitation were investigated. Experimental results as well as theoretical analysis demonstrated that electromagnetic (EM) enhancement and charge transfer (CT) both rebounded to the SERS effect of Ag@PPy nanoparticles. When near‐IR excitation (1064 nm) was used for the SERS measurements, the contribution from CT was amplified relative to that from EM because the energy of the near‐IR excitation is far from the surface plasmon resonance of the nanosized Ag particles. The increased doping level of PPy, leading to optimal energy matching between the Fermi levels of the Ag nanoparticles and the energy levels in PPy molecules, could obviouslyenhance the SERS signal. These results suggested that the SERStechnique wasan effective tool for investigating the doping effect and interface interaction in metal‐conductingpolymer composite nanoparticles. In particular, the SERS technique with near‐IR excitation could give more information regarding the contribution of the charge‐transfer mechanism to the spectral enhancement of this kind of system. Copyright © 2010 John Wiley & Sons, Ltd.     

Direct visual evidence for the chemical mechanism of surface‐enhanced resonance Raman scattering via charge transfer

We describe the chemical and electromagnetic enhancements of surface‐enhanced resonance Raman scattering (SERRS) for the pyridine molecule absorbed on silver clusters, in which different incident wavelength regions are dominated by different enhancement mechanisms. Through visualization we theoretically investigate the charge transfer (CT) between the molecule and the metal cluster, and the charge redistribution (CR) within the metal on the electronic intracluster collective oscillation excitation (EICOE). The CT between the metal and the molecule in the molecule–metal complex is considered as an evidence for chemical enhancement to SERRS. CR within the metal on EICOE is considered as an evidence for the electromagnetic enhancement by collective plasmons. For the incident wavelength from 300 to 1000 nm, the visualized method of charge difference density can classify the different wavelength regions for chemical and electromagnetic enhancement, which are consistent with the formal fragmented experimental studies. Copyright © 2008 John Wiley & Sons, Ltd.     

Darling–Dennison resonance of thiourea adsorbed on the silver electrode revealed by surface enhanced Raman spectroscopy

We report surface enhanced Raman spectroscopy (SERS) of Darling–Dennison resonance of thiourea on Ag electrode excited at 514.5 nm laser excitation. Darling–Dennison resonance indicates that two degenerate Raman modes interact with each other and their degenerate first‐order overtone modes obtain energy and appear in Raman spectra. Our study showed that the ratio of intensity of the Darling–Dennison resonance is up to 0.24 of its fundamental Raman intensity, when the applied electrode voltage is at –0.4 V versus the saturated calomel electrode. This phenomenon was also observed on the Ag island film surface at ambient condition. These observations demonstrated strong evidence for Darling–Dennison resonance band in SERS. The implications of these observations are also discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

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