过渡金属Hf_3~(2-)团簇的双重芳香性(σ与π)的理论研究

我们将芳香性概念扩展到第四副族元素铪组成的金属团簇Hf_3~(2-).运用两种密度泛函理论(B3LYP,B3PW91)和从头算方法MP2,对金属团簇Hf_3~(2-)的稳定结构与电子总能量(考虑了零点能ZPE)作了理论计算.计算的结果显示,在金属团簇Hf_3~(2-)的D_(3h)平面结构是最稳定的.并根据芳香性的平面、电子结构、核独立化学位移(NICS)、以及它们的分子轨道几个标准进行分析.分析的结果指出,2个离域化的σ电子及π电子,分别遵循4n+2电子计算规则,并且呈现出纯σ与π双芳香性.     

过渡金属Hf_3~(2-)团簇的双重芳香性(σ与π)的理论研究

我们将芳香性概念扩展到第四副族元素铪组成的金属团簇Hf_3~(2-).运用两种密度泛函理论(B3LYP,B3PW91)和从头算方法MP2,对金属团簇Hf_3~(2-)的稳定结构与电子总能量(考虑了零点能ZPE)作了理论计算.计算的结果显示,在金属团簇Hf_3~(2-)的D_(3h)平面结构是最稳定的.并根据芳香性的平面、电子结构、核独立化学位移(NICS)、以及它们的分子轨道几个标准进行分析.分析的结果指出,2个离域化的σ电子及π电子,分别遵循4n+2电子计算规则,并且呈现出纯σ与π双芳香性.     

全金属负离子团簇Ga42-、 In42-芳香性的磁特征与多重芳香性

运用密度泛函理论的两种方法(B3LYP、B3PW91)与二级微扰方法(MP2),对二价负离子全金属团簇Ga42-、In42-的稳定结构、振动频率与电子总能量作了计算.在此基础上,运用B3LYP与HF两种方法,着重对最稳定的正方形结构的Ga42-、In42-团簇的两种磁性质:各向异性磁化率与核独立化学位移进行了研究.计算结果表明,正方形结构Ga42-、In42-团簇具有很强的芳香性.接着对它们进行细致的分子轨道结构分析,揭示了正方形结构Ga42-、In42-团簇具有多重芳香性,一个非局域π分子轨道与两个非局域σ分子轨道对此两种金属团簇的芳香性都起了重要作用.     

阳离子X_3~+(X=Sc,Y,La)团簇d轨道芳香性的理论研究

运用密度泛函(DFT)和关联从头算(correlated ab initio)理论,对阳离子X_3~+(X=Sc、Y、La)和相关的中性X_3Cl(X=Sc、Y、La)团簇的稳定结构与芳香性进行研究.计算结果表明,X_3~+阳离子有两个稳定异构体:正三角型(D_(3h))和线型(D_(∞h)),其中正三角型为基态.对于中性的X_3Cl团簇,Sc_3Cl有三个稳定的异构体:三角金字塔型(C_(3v))、双齿型(C_(2v)-1)和C_(2v)-2型(图1);而Y_3Cl和La_3Cl只有2个稳定的异构体:三角金字塔型(C_(3v))和双齿型(C_(2v)-1).但这三个中性X_3Cl团簇的基态都是双齿型(C_(2v)-1)结构.对阳离子正三角型(D_(3h))基态结构进行共振能(RE)和核独立化学位移(NICS)的计算结果表明,X_3~+正三角型异构体展现出较高的芳香性.详细的分子轨道分析显示,正三角型Sc_3~+和Y_3~+阳离子有一个离域的π型分子轨道,显现出单π-芳香性;而正三角型La_3~+阳离子有一个离域的σ型分子轨道,显现出单σ-芳香性.X_3~+单π-芳香性或单σ-芳香性主要源于过渡金属Sc、Y和La的d原子轨道的贡献.另外,通过分子轨道分析还发现,当一个补偿阴离子Cl~-分别与Sc_3~+、Y_3~+阳离子结合成中性Sc_3Cl、Y_3Cl团簇时,其组成单元Sc_3~+、Y_3~+的芳香类型从原π-芳香性变为σ-芳香性,而当一个补偿阴离子Cl~-与La_3~+阳离子结合成中性La_3Cl时,其组成单元La_3~+原σ-芳香性保持不变.换言之,三个中性X_3Cl团簇都只显现出单σ-芳香性.     

X3+ (X=Sc, Y, La)阳离子团簇d轨道芳香性的理论研究

本文运用密度泛函（DFT）和哈特里-福克后（post-HF）理论,对三个阳离子X3+(X=Sc、Y、La) 和相关的三个中性X3Cl (X=Sc、Y、La)团簇的稳定结构与芳香性进行研究。计算结果表明,三个X3+阳离子有两个稳定异构体：正三角型(D3h)和线型(D∞h),其中正三角型为基态;对于三个中性的X3Cl团簇,Sc3Cl 有三个稳定的异构体: 三角金字塔型(C3v)、双齿型(C2v-1) 和 C2v-2型（图 1 e）;Y3Cl 和 La3Cl有2个稳定的异构体: 三角金字塔型(C3v) 和双齿型(C2v-1)。三者的基态都是双齿型(C2v-1)结构。接着,对阳离子正三角型(D3h)基态结构进行共振能（RE）和核独立化学位移（NICS）的计算。计算结果表明,X3+正三角型异构体展现出较高的芳香性。随后详细的分子轨道分析显示,正三角型Sc3+ 和Y3+阳离子有一个离域的π型分子轨道,显现出单π-芳香性;而正三角型La3+阳离子有一个离域的σ型分子轨道,显现出单σ-芳香性。并且,X3+ 的单π 芳香性或单σ芳香性主要是源于过渡金属Sc、Y和La中的d原子轨道的贡献。另外,通过详细分子轨道分析还发现,当一个补偿阴离子Cl-分别与Sc3+、Y3+、La3+阳离子结合时,中性Sc3Cl, Y3Cl团簇的芳香类型从组成单元Sc3+、Y3+的π-芳香性变为σ-芳香性,而中性La3Cl 团簇其组成单元La3+的σ-芳香性保持不变。总之,三个中性X3Cl团簇都只显现出单σ-芳香性。 （这篇文章是第15届全国原子分子会议稿件）     

Al_nC_4~(-/0)(n=2～4)团簇的结构和成键性质:光电子能谱和理论计算（英文）

本文采用尺寸选择的负离子光电子能谱与高精度理论计算,对Al_nC_4~(-/0)(n=2～4)团簇的结构和成键性质进行了研究.Al_2C_4~-团簇负离子的最稳定结构是一个C_(2v)对称的平面结构,其中两个C_2单元与两个铝原子分别相连.Al_2C_4~-团簇负离子的次稳定结构是一个线型结构,两个铝原子位于C_4线型结构两端,能量仅比最稳定结构高0.05 eV.中性Al_2C_4团簇是一个线型结构.Al_3C_4~-团簇负离子是一个平面结构,其中三个铝原子分别与两个C_2单元相连.而中性Al_3C_4团簇则是一个V字型结构.Al_4C_4~-团簇负离子和中性Al_4C_4团簇均为C_(2h)对称的平面结构,四个铝原子分别位于两个C_2单元的末端.Al_nC_4~(-/0)(n=2～4)团簇负离子的自适应自然密度配分的分析结果表明这些团簇中铝原子与C_2单元之间的化学键具有σ和π键特征.     

掺Be硼团簇BeB_n~(0/–)(n=10—15)的基态结构和性质

基于密度泛函理论结合粒子群优化算法程序CALYPSO研究了掺Be硼团簇BeB_n~(0/–)(n=10—15)的基态几何结构;然后采用密度泛函理论分析了最低能量结构的电子结构、极化率、红外光谱、紫外可见光谱特性.研究结果表明:BeB_(10)~(0/–),BeB_(11)~-,BeB_(12)~(0/-),BeB_(14)~-具有平面或准平面结构;BeB_(11),BeB_(13),BeB_(13)~-,BeB_(14)分别具有半三明治结构、圆锥结构、笼型结构、压扁的管状结构;BeB_(15)~(0/-)呈现手性对称结构.自然布居分析(NPA)表明掺杂Be原子将电子转移给硼原子.团簇的平均结合能分析可得,阴离子比相应中性团簇的稳定性强;另外,随着n的增加,中性和阴离子团簇的稳定性增强.准平面结构BeB_(10),BeB_(11)~-,BeB_(12)团簇的适应性自然密度划分(AdNDP)分析表明,s键促进了整个分子的稳定性,多中心π键进一步稳定了整个分子;另外,这三个团簇满足6个π电子Hückel规则(4m+2),具有芳香性.极化率分析可得,平面或准平面结构的每个原子的平均极化率大于其它结构,说明平面或准平面结构的电子离域效应较大;BeB_(13)~-,BeB_(14)~-具有较大的第一超极化率,说明具有较强的非线性光学响应.红外光谱分析表明这些团簇具有不同的特征峰,可用于鉴别这些结构;闭壳层结构团簇的紫外可见光谱在可见光波段都有吸收峰,开壳层结构团簇的紫外可见光谱在红外光波段都有吸收峰.     

负离子全金属团簇Ga2-4的芳香性的从头算理论研究

运用密度泛函理论的三种方法(B3LYP、B3PW91、PW91PW91)与Mller-plesset二级微扰方法(MP2)和极化分裂阶基基组6-311+G(3df),对二阶负离子全金属团簇Ga2-4与多种一阶负离子团簇MGa-4(M=Li、Na、Cu)稳定构型与振动频率作了计算,其中二阶负离子全金属团簇Ga2-4最稳定的构型是正方形结构(D4h).接着,从团簇结构、非局域π电子数目、分子轨道图形和Ga2-4同MGa-4在结构与谐振频率、谐振模式的对比等多方面论述了Ga2-4正方形结构(D4h))的芳香性特征.     

第一性原理对Ga_nN_n(n=2~5)小团簇的结构及电子性质的研究

利用密度泛函理论的B3LYP方法在6-31G*的水平上对GanNn(n=2~5)团簇的结构进行优化,得到了GanNn(n=2~5)团簇的最稳定结构.并对最稳定结构的电子性质、成键特性和极化率进行分析.结果表明,团簇的最稳定结构为平面结构,且存在着N2和N3单元,说明N-N键在团簇的形成过程中起着决定性的作用;能隙间隔为1.776~3.563eV,表明GanNn(n=2~5)团簇已具有了半导体的性质.     

对全金属La2-4团簇芳香性的从头算理论研究简

我们将芳香性扩展到全金属阴离子团簇La2-4.运用从头算方法(B3LYP/LANL2DZ,B3PW91/LANL2DZ and MP2/LANL2DZ)进行了结构优化.计算结果显示,阴离子团簇有两个同分异构体,一个是C2v结构,另一个是正方形D4h结构.进一步对能量的分析得出,D4h结构比C2v结构更稳定.对最稳定的D4h结构计算了核独立位移(NICS),结果显示正方形的La2-4环呈现强芳香性.详细的分子轨道(Mos)分析揭示正方形的La2-4环拥有四个独立的离域化成键系统,每一个系统拥有两个电子,分别满足4n+2芳香性电子计算规则,因此呈现四重芳香性.     

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.     

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.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.