一氟二氯乙烷分子在外电场中的光谱特征和解离特性

利用密度泛函理论在B3LYP/6-311+G(d, p)水平上研究不同外加电场下(-0.05～0.05 a.u.)一氟二氯乙烷分子的光谱特征和解离特性,其中包括该分子基态结构、总能量、偶极矩、最高占据轨道能级、最低空轨道能级、能隙、红外光谱、拉曼光谱、紫外可见光吸收光谱及C原子与Cl原子间势能曲线等数据在电场下的变化趋势。在y轴方向上,随着负向电场的增强,C原子与Cl原子核间距增长、最高占据轨道能级减小,体系总能量、最低未占据轨道能级、能隙先增大后减小,偶极矩先减小后增加。外加电场会影响一氟二氯乙烷分子红外光谱、拉曼光谱与紫外可见光吸收光谱的吸收强度和吸收峰频率,红外光谱、拉曼光谱与紫外可见光吸收光谱随着电场变化出现红移或蓝移现象。C原子与Cl原子间势垒随着负向电场增加逐渐减小,并在电场达到-0.05 a.u.时C原子与其中一个Cl原子发生断裂,当分子中一个C—Cl键断裂后,施加强度为-0.04 a.u.的电场时另外一个C—Cl键发生断裂,分子在电场下发生逐步解离,研究结果完善了一氟二氯乙烷分子受外电场影响的理论数据。     

特殊构型Si_2N_2分子团簇电致激发特性的密度泛函理论研究

以在可见光区有吸收峰的Cs构型的Si2N2分子团簇为研究对象,利用密度泛函B3LYP方法,在aug-ccpVTZ基组水平下优化得到了处于不同外电场中的Si2N2分子团簇的稳定结构.分析发现:在不同的外电场中,Si2N2分子构型对称性没有发生改变,均为Cs对称性,且都有6种振动模式;随着外电场强度的逐渐增大,Si2N2分子振动频率较低的前三种振动模式的频率略有减小,而后三种振动模式的频率逐渐增加;随着外电场强度的逐渐增大,在一定电场范围内最高占据分子轨道与最低空分子轨道的能隙值出现振荡,之后能隙值随着外电场强度的增大而减小.在此基础上,采用含时密度泛函TD-B3LYP方法研究了外电场对Si2N2分子吸收谱的影响规律.计算得到的吸收谱范围在紫外-可见光区,这与实验值相符合.随着外电场强度的逐渐增大,在可见光区吸收谱发生红移,最大跃迁振子强度逐渐增大.结果表明,施加外电场有利于Si2N2分子在可见光区的吸收,也有利于操控分子特定激发态的电子状态,进而调节相应的跃迁光谱特性,可达到获得所需特定波长的要求.     

外电场下L-茶氨酸分子的结构特征与光谱性质

L-茶氨酸(N-乙基-L-谷氨酰胺)是一类具有降压、抗氧化的非蛋白氨基酸,研究外场下它的结构和光谱特征有助于人们更好地认识L-茶氨酸分子的性质.基于密度泛函理论,利用B3LYP方法,在6-311g(d,p)基组水平上对L-茶氨酸分子进行几何构型优化,在此基础上计算L-茶氨酸分子在不同外电场下(0～0.0125 a.u.)的分子各键长与振动频率,得到对应的红外光谱.同时,在相同的基组下采用含时密度泛函方法(TD-DFT)计算外电场对分子的激发态、前线轨道和能隙的影响.结果表明:分子结构及其紫外、红外光谱都随外电场强度发生变化.随外电场的增加,伸缩振动频率红移,弯曲振动频率蓝移;最高占据轨道的能量(E_(HOMO))与最低空轨道的能量(E_(LUMO))发生改变,前线轨道能隙先小幅增加后随电场减小,分子活性先减小后增强;紫外吸收光谱先蓝移后红移.本研究对L-茶氨酸分子的检测、合成及其生物活性的研究可提供理论依据.     

外电场下L-茶氨酸分子的结构特征与光谱性质

L-茶氨酸(N-乙基-L-谷氨酰胺)是一类具有降压、抗氧化的非蛋白氨基酸,研究外场下它的结构和光谱特征有助于人们更好地认识L-茶氨酸分子的性质.基于密度泛函理论,利用B3LYP方法,在6-311g(d,p)基组水平上对L-茶氨酸分子进行几何构型优化,在此基础上计算L-茶氨酸分子在不同外电场下(0～0.0125 a.u.)的分子各键长与振动频率,得到对应的红外光谱.同时,在相同的基组下采用含时密度泛函方法(TD-DFT)计算外电场对分子的激发态、前线轨道和能隙的影响.结果表明:分子结构及其紫外、红外光谱都随外电场强度发生变化.随外电场的增加,伸缩振动频率红移,弯曲振动频率蓝移;最高占据轨道的能量(E_(HOMO))与最低空轨道的能量(E_(LUMO))发生改变,前线轨道能隙先小幅增加后随电场减小,分子活性先减小后增强;紫外吸收光谱先蓝移后红移.本研究对L-茶氨酸分子的检测、合成及其生物活性的研究可提供理论依据.     

外电场下二氧化硫的分子结构及其特性

以6-311++g(3d, p)为基组, 采用B3P86方法研究了不同外电场(-0.04-0.04 a.u.)对SO₂分子基态的几何参数、电荷分布、能量、电偶极距、最高占据轨道(HOMO)能级、最低占据轨道(LUMO)能级及能隙的影响, 在优化构型的基础上, 采用含时密度泛函(TD-B3P86)方法研究了SO₂分子在外电场作用下前9个激发态的激发能、跃迁波长和振子强度. 研究表明: SO₂的几何参数与电场强度大小及方向均有明显的依赖关系. 电场由-0.04 a.u. 变化至0.04 a.u.时, 体系的总能量先增加后减小; 偶极矩先减小后增加; HOMO能级一直减小; LUMO能级先增加后减小; 能隙先增加后减小. 激发态的激发能、跃迁波长和振子强度与电场关联均较为复杂, 说明SO₂的激发特性易受外电场影响.     

基于第一性原理研究聚对苯二甲酸乙二酯的电子结构和光学性质

基于密度泛函理论的第一性原理方法来研究聚对苯二甲酸乙二酯(PET)分子的电子结构和光学特性,结果表明:PET分子的轨道贡献主要是由O原子的2p轨道和C原子的2p轨道组成,而由能带结构计算得到的能隙比实验值要偏小;对于最高占据轨道,电荷密度主要分布在苯环两侧;而对于最低未占据轨道,最高的电荷密度主要分布在苯环上。由吸收光谱的吸收边得出的能隙与计算能带结构得到的结果一致,并解释了介电函数峰的形成和其它光谱特性的联系。     

外电场下二氧化锆的分子结构及其特性

对O原子采用6-311++G*基组,Zr原子采用aug-cc-pVTZ-PP基组,利用密度泛函(B3P86)方法优化得到了ZrO2分子的稳定构型,并研究了不同外电场(0—0.025 a.u.)作用下ZrO2基态分子键长、能量、电荷分布、偶极矩和能级的变化规律.在优化构型的基础上,利用含时密度泛函(TD-B3P86)方法研究了ZrO2分子在外电场作用下前6个激发态的激发能、跃迁波长和振子强度的激发特性.研究结果表明:随着电场强度的增大,Zr—2O的键长增大,而Zr—3O的键长均匀减少,总能量降低,偶极矩增大;最高占据轨道能量基本保持不变,最低未占据轨道和能隙均减小.电场的增大使得激发能减小,各个激发态跃迁波长均发生不同程度的红移现象,因而,利用外电场可以控制ZrO2的发光光谱范围在可见-红外区域扩展.     

ZnS电子结构及电性能应力效应的研究

基于广义梯度近似平面电子波函数密度泛函理论计算的方法研究了无压力下和在1 GPa外压应力下闪锌矿结构ZnS的能带结构、电子状态密度、结合状况和介电性能。结果表明在外加1 GPa压力时闪锌矿结构ZnS晶格常数由2.7605减小到2.7049,对称性不变.在外压1 GPa应力下ZnS仍呈直接带隙的能带结构,带隙宽度较未加压力时减小到1.698 e V.在外加1 GPa压应力下ZnS费米能附近的载流子浓度大大增加,更容易发生跃迁而产生电迁移和光电现象。外加1 GPa压力时Zn-S键长由2.3905减小到2.3405,Zn-S成键数量由1.820个增加到1.860个.ZnS硫化物在紫外和可见光波段主要存在四个介电吸收峰,外加1 GPa压应力下位于170 nm和210 nm附近的直接跃迁介电吸收峰强度降低.     

外场作用下蒽分子的激发特性研究

蒽(anthracene)具有良好的热稳定性以及较高的荧光量子产率的优点, 是最早用于研究有机发光器件(organic light-emitting device, OLED)的材料之一. 在本文中, 主要利用量子化学方法研究了不同外电场对蒽分子激发特性的影响规律. 首先采用密度泛函理论(density functional theory, DFT)在6-311G(d, p)基组水平上对蒽分子基态结构进行优化, 基于稳定基态结构, 利用含时密度泛函(time-dependent density functional theory, TDDFT)以及同一基组水平, 计算出蒽分子的前十个激发态的激发能、跃迁偶极矩、振子强度和紫外吸收光谱等数据. 然后以密度泛函B3P86方法优化出的不同外电场下蒽分子基态结构为基础, 使用TDDFT方法研究了不同外电场对蒽分子前线轨道能级和激发特性的影响规律. 结果显示, 无场时蒽分子在紫外区域234.50 nm处有一个较强的吸收峰, 对应基态电子跃迁至第5激发态吸收光子波长; 在外电场作用下, 蒽分子电子由基态跃迁到激发态的各项光谱参数均有显著变化, 加场后蒽分子的吸收光谱发生了红移, 由紫外波段移向了紫外–可见光波段, 与实验值相符合. 分子前线轨道的计算结果也表明蒽分子的最高占据轨道(highest occupied molecular orbital, HOMO)和最低未占据轨道(lowest unoccupied molecular orbital, LUMO)能量差值在不同电场下存在差异. 关键词： 蒽 外电场 激发特性     

并五苯分子光谱和激发态的密度泛函理论研究

采用密度泛函理论对并五苯分子做理论研究.在几何结构优化的基础上,对其进行频率分析得到了分子的红外光谱和喇曼光谱,并对谱线中的各峰值做了具体指认,同时也得到了分子的最高占据轨道和最低空轨道能隙为2.17 eV.利用含时密度泛函理论对其激发态计算,得到最低十个跃迁允许的单激发态.对前线分子轨道最高占据轨道和最低空轨道分析得到,C-C原子之间形成离域π键.结果表明：并五苯是一种良好的有机半导体材料,并具有很好的发光性能.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Research on beamforming method for dual-line array with space mismatch between the two line arrays

The performance of port/starboard discrimination of dual-line array will be seriously degraded when the space between the two line arrays of the dual-line array is mismatched. The directivity function of the delay-sum and delay-subtract beamforming is deduced and the port/starboard discrimination of the delay-sum and delay-subtract beamforming is also studied both under the ideal status and the status under which the space between the two line arrays of the dual-line array is mismatched. Analysis results show the delay-subtract beamforming has better performance of port/starboard discrimination. At last, the sea trial results demonstrate the theoretical results.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Retrieval of ultraviolet skylight radiances and O3 slant column densities from balloon-borne limb spectrometer

With a novel light-weight and absolutely calibrated ultraviolet （UV） spectrometer, UV skylight radiances and O3 slant column densities are measured by balloon-borne limb measurements in Xinjiang area, China. UV skylight radiances measured at the height of 31 km are compared with the results from Modtran in the wavelength range from 290 to 420 nm. O3 slant column densities are derived from radiance spectra in the Huggins bands （320 - 335 nm） using differential optical absorption spectroscopy method. And the parameter exhibits a good correlation with the same value simulated by radiative transfer model （Tracy）. The O3 profile simultaneously measured by an O3 sonde is used as input in Tracy calculations. The O3 sonde is launched on the same balloon.