(XB2)2(X=Al, Be, Na, Mg)团簇的密度泛函研究

用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G*基组水平上对(XB2)2(X=Al,Be,Na,Mg)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.并对最稳定结构的电子结构、振动特性、成键特性和电荷特性等进行了理论研究.结果表明,团簇的几何结构大多是平面结构,通常是B-B键和B-X键共存,较少出现X-X键.团簇的稳定结构中通常是几个呈负电性的B原子形成一个负电中心,而其他B原子和X原子处在端位,且显正电性.     

CN红带A 2Пi-X 2Σ+(6, 1)和(7, 2)带振转光谱研究

通过微量CH3CN(36 Pa)与He(660 Pa)混合气体交流Penning辉光放电获得CN自由基分子, 采用光外差-磁旋转-浓度调制光谱技术, 在可见光波段16 850～17 480 cm-1进行了转动分辨光谱测量, 分别标识了CN分子红带A 2Пi-X 2Σ+(6, 1)和(7, 2)138条和118条的转动光谱(其余光谱为C2自由基及CN红带(8, 3)带光谱). 理论拟合分子常数时考虑电子态间的微扰作用, 采用有效哈密顿量矩阵对角化获得了A 2Пi(ν=6, 7)态更精确的分子常数及电子态A 2Пi(ν=7)与 X 2Σ+ (ν=11)之间的微扰常数ξ, η, 总体拟合方差均小于实验误差0.007 cm-1, 表明拟合结果是非常精确的.     

Structure and magnetic properties of the intermetallic La2Co17−xMox (x=0.5, 1, 1.5, 2) and La2Co16−yFeyMo (y=0, 1, 2, 3, 4, 6) compounds

The effect of Mo and Fe atoms on the crystal structure and magnetic properties of the intermetallic La₂Co_17−xMo_x (x=0.5, 1, 1.5, 2), and La₂Co_16−yFe_yMo (y=0, 1, 2, 3, 4, 6) compounds have been studied by X-ray diffractometry, magnetic measurements and Mössbauer spectroscopy. All samples belong to the rhombohedral Th₂Zn₁₇-type structure and their lattice parameters a and c increase both with Mo and Fe content. From the La–Co–Mo samples only the one with x=0.5 presents planar anisotropy, whereas from the La–Co–Fe–Mo samples only the y=1 has uniaxial anisotropy. The magnetization M_S and the Curie temperature T_C decrease upon Mo substitution, whereas the anisotropy field H_A does not change significantly. In the Fe-substituted compounds M_S increases, but the Curie temperature increases slightly for 0⩽y⩽4 but decreases in y=6. The low temperature M–T curve shows that the samples La₂Co_16.5Mo_0.5, and La₂Co₁₀Fe₆Mo present a spin reorientation transitions at 70 and 260 K, respectively. Mössbauer samples were obtained for all Fe-containing samples in the temperature range 20–300 K. Above 260 K a jump in the values of the hyperfine fields and quadrupole splitting parameters is observed which can be associated to the spin reorientation.     

A comparison of the197Au Mössbauer spectra of MAu (M=K,Rb, Cs) with (2, 2, 2-crypt M) Au

Gold-197 Mössbauer spectroscopy has been used to investigate the MAu system (M=K, Kb, Cs). Of the 11 alloys RbAu and CsAu give Mössbauer spectra consistent with cubic gold environments, while (2,2,2-crypt M) Au, (M=K, Pb, Cs) all have cubic gold environments. Comparison of the isomer shifts for the crypted and uncrypted salts leads to the conclusion that in RbAu and CsAu considerable electron density is removed from the gold 5d orbitals.     

Tensor Force Manifestations in ab Initio Study of the 2H(d, γ)4He, 2H(d, p)3H, and 2H(d, n)3He Reactions

The ²H(d, γ)⁴He capture reaction and the ²H(d, p)³H and ²H(d, n)³He transfer reactions at very low energies are studied in an extended microscopic cluster model with a realistic nucleon–nucleon force. Our results show that the tensor force in realistic interactions plays an essential and indispensable role to reproduce the very low-energy astrophysical S factor of these reactions.     

Tensor force manifestations in ab initio study of the 2H(d,γ)4He, 2H(d,p)3H, and 2H(d,n)3He reactions

The (2)H(d,p)(3)H, (2)H(d,n)(3)He, and (2)H(d,γ)(4)He reactions are studied at low energies in a multichannel ab initio model that takes into account the distortions of the nuclei. The internal wave functions of these nuclei are given by the stochastic variational method with the AV8' realistic interaction and a phenomenological three-body force included to reproduce the two-body thresholds. The obtained astrophysical S factors are all in very good agreement with the experiment. The most important channels for both transfer and radiative capture are identified by comparing to calculations with an effective central force. They are all found to dominate thanks to the tensor force.     

(XB2)2(X=Al, Be, Na, Mg)团簇结构与性质的密度泛函研究

用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G·基组水平上对(XB2)2(X=Al,Be,Na, Mg)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.并对最稳定结构的电子结构、振动特性、成键特性和电荷特性等进行了理论研究.结果表明,团簇的几何结构大多是平面结构,通常是B-B键和B-X键共存,较少出现X-X键.团簇的稳定结构中通常是几个呈负电性的B原子形成一个负电中心,而其他B原子和X原子处在端位,且显正电性.     

低能He-H2(D2,T2)碰撞分波截面计算

采用Tang Toennes势模型 ,当入射氦原子能量是E =0 .0 5eV时 ,计算了He -H2 (D2 ,T2 )弹性分波截面和非弹性激发分波截面随量子数的变化。     

F_2~(ep)(x,Q~2)-F_2~(en)(x,Q~2)的行为和标度性破坏参数

利用在文章[1]中给出的强子的价夸克分布函数的解析表达式,我们讨论了电生过程的非单态分量,F_2~(ep)-F_2~(en),标度性破坏参数,以及一些其它的量。文中也给出了与实验数据的比较。在前文中,我们利用A-P方程在合理的近似下得到了强子价夸克分布函数的解析表达式。在本文中,我们用它来讨论电生中的非单态分量,F_2~(ep)-F_2~(en),标度性破坏参数以及一些其它的量。     

C-15结构(Hf,Zr,Ta)V_2和(Hf,Zr,Nb)V_2合金超导转变的压力效应研究

本文研究了C-15结构化合物(Zr_(0.5)Hf_(0.5)-xTa_x)V_2(x≤0.2)和(Hf_(0.5)Zr_(0.5-x)Nb_x)V_2(x≤0.2)的超导转变温度T_c及其压力效应T_c/P。报道了实验方法与结果。与(Hf_(1-x)Ta_x)V_2和(Zr(1-x)Ta_x)V_2的情况不同,在(Zr_(0.5)Hf_(0.5-x)Ta_x)V_2中Ta的引入使常压下的T_c下降,然而T_c/P却大为提高。因此高压下Zr_(0.5)Hf_(0.45)Ta_(0.05)V_2的T_c反而比Hf_(0.5)Zr_(0.5)V_2更高。导出了一个基于角动量分波表象能带论方法的描述压力效应的新关系式。它指出导带电子波函数中的高角动量成分变化对T_c的压力效应影响比较重要。这个公式有助于理解上述复杂的实验现象,并能合理地解释某些元素(如Cs,Ba,La等)的T_c随压力剧增的事实。     

Total cross sections of electron scattering by molecules NF3, PF3, N(CH3)3, P(CH3)3, NH(CH3)2, PH(CH3)2, NH2CH3 and PH2CH3 at 30–5000 eV

Total cross sections of electron scattering by eight molecules NF₃, PF₃, N(CH₃)₃, P(CH₃)₃, NH(CH₃)₂, PH(CH₃)₂, NH₂CH₃ and PH₂CH₃, which have some structural similarities, are calculated at the Hartree-Fork level by the modified additivity rule approach [D.H. Shi, J.F. Sun, Z.L. Zhu, H. Ma, Y.F. Liu, Eur. Phys. J. D 45, 253 (2007); D.H. Shi, J.F. Sun, Y.F. Liu, Z.L. Zhu, X.D. Yang, Chin. Opt. Lett. 4, 192 (2006)]. The modified additivity rule approach takes into considerations that the contributions of the geometric shielding effect vary as the energy of incident electrons, the dimension of target molecule, the number of electrons in the molecule and the number of atoms constituting the molecule. The present investigations cover the impact energy range from 30 to 5000 eV. The quantitative total cross sections are compared with those obtained by experiments and other theories. Excellent agreement is observed even at energies of several tens of eV. It shows that the modified additivity rule approach is applicable to carry out the total cross section calculations of electron scattering by these molecules at intermediate and high energies, in particular over the energy range above 80 eV or so. It proves that the microscopic molecular properties, such as the geometrical size of the target and the number of atoms constituting the molecule, are of crucial importance in the TCS calculations. The new results for PH(CH₃)₂ and PH₂CH₃ are also presented at energies from 30 to 5000 eV, although no experimental and theoretical data are available for comparison. In the present calculations, the atoms are still represented by the spherical complex optical potential, which is composed of static, exchange, polarization and absorption terms.     

Structural, thermal, and electrical properties of (100?x) ZrO2 (x) Bi2O3 compound

Composition (100?x) ZrO₂ (x) Bi₂O₃ (x?=?15, 20, 25) is synthesized by solid-state reaction method to study the effect of Bi₂O₃ doping on ZrO₂. The as-prepared samples are characterized by various methods. The X-ray diffraction pattern of all these samples exhibits three phases, namely, m-ZrO₂, ??_III-Bi₂O₃, and ??-Bi₂O₃. The differential thermal analysis curves do not show any phase transition/decomposition, which clearly indicated the stabilization of ??-Bi₂O₃ phase. The conductivity changes in all the samples are discussed in terms of different phase formations and their volume fractions. The microstructural and energy dispersive analyses indicate the presence of different phases. A maximum conductivity at high temperature (800?°C) was observed for the x?=?25 composition, i.e., ???=?4.21?×?10^?2 S/cm.     

Are (0, 2) models string miracles?

String theory exhibits a number of string miracles. These are “accidental” relations between couplings in the low-energy effective action which cannot be understood in terms of the symmetries of that action. It is shown that the existence of (0, 2) models need not be a string miracle, but can often be understood in terms of a discrete R symmetry. This understanding points to many new (0, 2) models, including some with gauge group SU(3) × SU(2) × U(1). Discrete R symmetries also protect some massless particles from acquiring a mass at special points in the moduli space of the conformal field theory. From a two dimensional point of view, this can be understood in terms of index theorems not only in the R but also in the NS sector. An important tool in the study of string compactification and conformal field theory is the perturbative expansion around a conformal field theory. We prove that the expansion of the space time superpotential around a space-time supersymmetric vacuum does not miss non-perturbative effects (as long as we do not expand around a boundary of moduli space). This shows that certain results which have been obtained to all orders in this expansion are exact. Also, it shows that the construction of the (0, 2) models in perturbation theory around (2, 2) models is exact as well.     

RECENT PROGRESS OF(e,2e) SPECTROSCOPY

Recent progress of(e,2e)spectroscopy,or Electron Momentum Spectros-copy(EMS),on laser excited oriented atoms,large bio-organic moleculesand thin films is reviewed.     

(p,n)和(p,2n)反应激发函数的系统学研究

从普朗克(Planck)黑体辐射公式和实验测量数据出发,采用唯象的方法提出了包含两个可调参量,入射质子能量从阈能到150MeV,靶核质量数在44相似文献   

(Sr,Co,Nb)掺杂SnO2压敏电阻的电学非线性

研究了Sr对新型(Co, Nb)掺杂SnO2压敏材料微观结构和电学性质的影响.当SrCO3的含量从零增加到1.50mol%时,(Co, Nb)掺杂SnO2压敏电阻的击穿电压从240V/mm猛增到1482V/mm.样品的微观结构分析发现, 当SrCO3的含量从零增加到1.50 mol%时, SnO2的晶粒尺寸迅速减小.晶界势垒高度测量揭示,SnO2晶粒尺寸的迅速减小是击穿电压急剧增高的主要原因.对Sr含量增加引起SnO2晶粒减小的根源进行了解释.掺杂1.50 mol% SrCO3的SnO2压敏电阻非线性系数为21.4,击穿电压高达1482V/mm.     

(Bi,Cd)Sr_2(Ln,Ce)_nCu_2O_y超导体及界面反应的光电子能谱研究

用光电子能谱研究了(Bi.Cd)Sr_2(Ln,Ce)_(?)Cu_2O_y的电子结构,以及其与铝之间的反应.芯能级结果表明:(Bi,Cd)Sr_2(Ln,Ce)_(?)Cu_2O_y系列中n=1,2和3三种材料的结果基本一致,并且类似其它超导材料中相同元素的芯能级结果.在(Bi,Cd)Sr_2(Ln,Ce)_(?)Cu_2O_y与铝的界面处,铝与(Bi,Cd)Sr_2(Ln,Ce)_(?)Cu_2O_y中的元素发生强烈反应,Bi—O,Sr—O和Cu—O键受到破坏,铜的价态从+2变为+1,并且同时伴随着超 关键词：     

Ar~ ,Ar~(2 ) Li,Na碰撞过程中的靶激发

本文对Ar~ ,Ar~(2 ) Li,Na碰撞过程中的靶激发过程进行了实验研究。通过光学多道分析系统对这些碰撞体系所发光谱进行了绝对测量。在能量范围q×(15—150)keV内给出了相应谱线的发射截面积Li(2p),Na(3p)激发截面。