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     

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     

(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     

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.     

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。     

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     

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     

基于键极化加和模型及其实验修正方法的超拉曼微观极化率张量元微分的简化方案-C2v对称性

相干反斯托克斯拉曼光谱(CARS) 和相干反斯托克斯超拉曼光谱(CAHRS)等高阶非线性光谱技术已经应用在动力学过程、基因表达谱筛选、高分辨率光谱分析等诸多领域。但因其涉及到的高阶微观极化率张量元数量众多,对其光谱信号进行定量分析非常困难。文献通过理论分析将CARS和CAHRS的微观极化率张量元分解为拉曼微观极化率张量元微分α′_i′j′和超拉曼微观极化率张量元微分β′_i′j′k′的乘积,将高阶光谱定量分析的困难简化为对低阶光谱的分析。该研究处理了具有C_2v对称性分子基团,提出一种利用键极化加和模型及其实验修正的方法简化超拉曼微观极化率张量元微分β′_i′j′k′比值的方案。首先利用键极化加和模型方法,在对C_2v分子基团局域模式假设的基础上,进行单键的局域模式假设,通过对单键伸缩振动进行简正振动模式的分析,并与单键的偶极矩表达式进行比较,得到单键的超拉曼微观极化率张量元微分β′_i′j′k′。在单键β′_i′j′k′结果的基础上利用键极化加和模型,对C_2v分子基团进行对称性分析,将基团中两个单键伸缩振动的β′_i′j′k′耦合,得到C_2v分子基团对称振动和反对称振动两种简正振动模式的超拉曼微观极化率张量元微分β′_i′j′k′的表达式。在此基础上对C_2v分子基团对称振动和反对称振动的β′_i′j′k′表达式进行理论推导,结合对应振动模式下不同偏振组合的超拉曼退偏率ρ_HR-SS和ρ_HR-AS及HV偏振组合时实验测量的超拉曼光谱强度比,得到超拉曼实验修正的C_2v分子基团β′_i′j′k′之间的比值。再结合文献中拉曼实验修正的拉曼微观极化率张量元微分α′_i′j′之间的比值,即可得到C_2v分子基团CARS和CAHRS的微观极化率张量元之间的比例关系,为定量分析高阶非线性光谱信息提供理论基础。     

单晶锗表面键合光敏染料的研究

本文在烯丙醇单体上进行了两种一甲川菁的合成,并用一种新的化学键合法将两种一甲川菁染料键合在抛光的半导体单晶锗表面。将键合有光敏染料的锗片进行了激光Raman光谱及XPS谱测试,结果表明,与对照锗片相比,键合后的锗片表面,锗衬底的一级拉曼峰强度减少,并在600～3200cm~(-1)范围内出现了与键合颜料分子相应的拉曼频移;在XPS谱中,分别进行了C,N,O,S,卤素等原子的谱图分析,证实了键合颜料后半导体单晶锗表面增加了C—N,S—C,C—O等键,结果与键合的颜料分子结构相符,表明两种光敏染料通过锗氧键共价键合于锗表面。     

非共振条件下单壁碳纳米管拉曼散射强度的计算

利用非共振情况下的键极化模型理论，对单壁碳纳米管的拉曼光谱强度进行了研究.考察了碳纳米管结构、入射光和散射光的偏振方向以及管轴的取向对散射光强度的影响.计算结果表明，光的偏振方向对拉曼散射强度影响较大，而手性对拉曼光谱的影响较小.针对碳管样品的实际情况，给出了无规取向碳管的拉曼散射光谱. 关键词： 碳纳米管 拉曼散射 声子 键极化     

The evaluation of temporal electronic structures of nonresonant Raman excited virtual state of thiourea

An algorithm has been introduced to calculate molecular bond polarizabilities of thiourea, which supply essential electronic information about the nonresonant Raman excited virtual states. The main dynamical behaviour of the excited virtual states of thiourea is that the Raman excited electrons tend to flow to the N-H bonds and C-N bonds from the S-C bonds because of the electronic repulsion effect. The difference in Raman excited electron relaxation time of thiourea under 514.5-nm and 325-nm excitations has been observed, which quantitatively shows that the Raman scattering process is dependent on the wavelength of the pumping laser. Finally, the distribution of the electrons at the final stage of relaxation is given out through the comparison between the bond electronic densities of the ground states and the bond polarizabilities after deexcitation.     

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.     

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.     

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.     

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.