在193 nm关于Si2分子的离子解离动力学的成像研究

在193 nm的单色激光实验中,本文利用时间切片离子速度成像技术,研究了经193 nm双光子电离得到的Si₂⁺的解离反应动力学过程. 根据实验得到的Si⁺离子的速度成像,观测到了两种离子直接解离通道：Si(³P_g)+Si⁺(²P_u)和Si(¹D₂)+Si⁺(²P_u). 电子基态的Si₂分子处于v=0∽5的振动态上,其经过双光子电离后激发到Si₂⁺离子的多个电子激发态势能面,生成主要通道Si(³P_g)+Si⁺(²P_u),其中v=1的解离信号最强. 此外,由于势能曲线2²Π_g与3²Π_g相同对称性引起的避免性势能面交叉,生成次要反应通道Si(¹D₂)+Si⁺(²P_u). 通道Si(¹D₂)+Si⁺(²P_u)的产物亦可以由生成的基态Si₂⁺(X⁴Σ_g^-)吸收一个193 nm光子后解离得到,其对应产物则具有更大的动能.     

J/ψ强子衰变过程的矩分析

本文给出了过程e⁺+e^－→J/ψ→V+X,V→P₁P₂或P₁P₂P₃和X→pp的角分布螺旋度形式,并在此基础上进行了矩分析,得到了若干关系式,有助于确定玻色共振态X的自旋J_x以及过程J/ψ→V+X的螺旋度振幅之比.     

单粒子薛定谔液体和形变核的转动惯量

将单粒子薛定谔液体理论应用于轴对称形变核的集体运动.也给出了一个相反的例子,即在各向异性谐振子势中处于稳定形变的任意数目的独立核子.而且,通过填充与主量子数n_x,n_y和n_z的可能值相应的单粒子态来构成s-d壳偶偶核:²⁰Ne,²⁴Mg,²⁸Si,³²S和³⁶Ar的基态,并计算了作为谐振子参数hω_x,hω_y和hω_z的函数的这些核的推转模型、刚体模型和稳态模型转动惯量.这些谐振子参数用与质量数A、中子数N、质子数Z和形变参数β有关的非形变参数hω00来描述.这些核的推转模型转动惯量的理论计算结果与实验数据符合甚好.而且,所考虑的轴对称形变核可能是扁椭球形的,也可能不是扁椭球形的,其中²⁴Mg是惟一高度形变的.²⁰Ne和²⁴Mg这两个核的刚体模型和稳态模型转动惯量也与实验数据符合甚好.     

Theoretical Study of Interaction Between S2 and SiHx (x=1, 2, 3) in Porous Silicon

用密度泛函B3LYP/lanl2dz方法研究了S₂分子与多孔硅中SiH_x (x=1, 2, 3)的相互作用, 构建了表面掺杂有CH₃,Si-O-Si和OH结构的多孔硅模型. 当S₂分子处于模型不同位置时,通过分析结合能和电子迁移发现S₂分子与SiH_x (x=1, 2, 3)的相互作用强于S₂分子与CH₃和OH的相互作用. 利用过渡态理论研究了Si₂H₆+S2→H₃SiH₂SiS+HS反应,得到反应势垒为50.2 kJ/mol.     

矩分析法与ξ(2220)

为减少几何接收度的影响,提高精度,我们引进矩的赝标介子角分布H_J(jm,θ).对于辨别ξ(2220)的自旋为2还是4,要比通常的投影赝标介子角分布W_J(θ)灵敏.我们还给出了矩分析所需的矩,以及直接用矩的关系式表示的螺旋度振幅之比x_J和y_J.     

Kl3介子衰变

本文通过强作用K-π中间态,利用色散关系理论计算了Г(K_μ3⁺)/Г(K_α3⁺),Г(K₂⁰→πμ⁺ν)/Г(K₂⁰→πe⁺ν),{Г(K₂⁰→πe⁺ν)+Г(K₂⁰→πe^-ν)}/Г(K_α3⁺)分支比及K_μ3⁺衰变中的μ谱,当选择定则|ΔI|=1/2及ΔS=+ΔQ被破坏,并且I_z=1/2及I_z=3/2的振幅f^{3/2 1/2}(0)及f^{3/2 3/2}(0)不等时,上述分支比与实验能很好符合。在本文的理论中,形式因子不是常数。     

f4—f7的波函数

本文用算子L⁺,S⁺,Q,R求得了f^4-7的波函数。并讨论了通过表象变换计算库仑能、自旋轨道作用和晶场,以及使希土离子能量矩阵对角化的方案。     

确定ξ(2230)自旋的一种新方法

本文得到了过程e⁺e^－→J/ψ→γB(J^η)、B(J^η)→P_{1P2的矩的光子角分布,提供了确定ξ(2230)自旋的新途径.}     

pp湮没成双介子的相对论处理

本文在³S₁模型基础上,采用相对论跃迁势和夸克(反夸克)旋量波函数,计算了pp→π⁺π^－和K⁺K^－的反应截面和角分布.     

Experimental and Theoretical Study of Hydrogen Atom Abstraction from Ethylene by Stoichiometric Zirconium Oxide Clusters

使用配有团簇产生和化学反应源的飞行时间质谱装置,研究了锆氧阳离子团簇Zr_xO_y⁺和乙烯的反应. 在这个反应中,发现了产物(ZrO₂)_xH⁺ (x=1～4). 使用密度泛函理论研究了乙烯在Zr₂O₄⁺上的反应通道,发现除了通常的氧转移反应外,乙烯脱氢反应也可以发生,从而支持观察到的产物(ZrO_{2相似文献}   

Thermal entanglement in the XYZ model for a two-qutrit system

The negativity as a measure of thermal entanglement was studied for a two-qutrit spin-1 anisotropic Heisenberg XYZ chain with Dzyaloshinskii-Moriya (DM) interaction in a homogeneous magnetic field in detail. An analytical expression was found for the negativity and then the thermal variations of negativity were investigated in full detail for given values of the DM interaction parameter D_z, the external magnetic field B, the measure of the anisotropy on the xy-plane γ = (J_x − J_y)/(J_x + J_y), a parameter J = (J_x + J_y)/2 and the bilinear interaction parameter J_z along the z-axis.     

The anisotropic 3D Ising model

An expression for the free energy of an (001) oriented domain wall of the anisotropic 3D Ising model is derived. The order--disorder transition takes place when the domain wall free energy vanishes. In the anisotropic limit, where two of the three exchange energies (e.g. J_x and J_y ) are small compared to the third exchange energy (J_z ), the following asymptotically exact equation for the critical temperature is derived, sinh(2J_z /k _B T _c)sinh(2(J_x ?+?J_y )/k _B T _c))?=?1. This expression is in perfect agreement with a mathematically rigorous result (k _B T _c/J_z ?=?2[ln(J_z /(J_x ?+?J_y ))?ln(ln(J_z /(J_x ?+?J_y ))?+?O(1)]^?1) derived earlier by Weng, Griffiths and Fisher (Phys. Rev. 162, 475 (1967)) using an approach that relies on a refinement of the Peierls argument. The constant that was left undetermined in the Weng et al. result is estimated to vary from ～0.84 at ((H_x ?+?H_y )/H_z )?=?10^?2 to ～0.76 at ((H_x ?+?H_y )/H_z )?=?10^?20.     

Tc级数解的收敛性质

本文证明了,当|z_ph|c级数解的收敛圆是由奇点决定的,但是只要1/λ<[0.63+3μ⁺(1/Λ₁)] 1/(Λ₁),T_c级数解在收敛圆外仍然是个很好的渐近展开式,其中1/Λ₁=min(|z|,1);μ⁺(x)=(1-2μ^*x)μ^*。 关键词：     

Quantum Monte Carlo Investigation of the magnetic properties of weakly interacting antiferromagnetic chains with an alternating exchange interaction with spin S = 1/2

An approximation dependence of the spontaneous magnetic moment at a site, σ/σ(0) ? 1 = and the antiferromagnet-singlet state phase boundary, J ₂/J ₁ = 0.52(3)δ, are determined by the quantum Monte Carlo method in the self-consistent sublattice molecular field approximation for weakly inter-acting (J ₂) antiferromagnetic chains with spin S = 1/2 and alternating exchange interaction (J ₁ ± δ). The Néél temperature and a number of critical temperatures which could be related with the filling energy of two singlets (ΔS ^z = 0) and one triplet (ΔS ^z = 1) spin bands, each of which is split by the sublattice field (h ^{x, y} ≠ h ^z into two subbands, are determined on the basis of the computed correlation radii of the two-and four-spin correlation function, the squared total spin 〈 (S ^z)²〉 with respect to the longitudinal components, the dimerization parameter, and the correlation functions between the nearest neighbors with respect to longitudinal and transverse spin components. On the basis of the Monte Carlo calculations, the critical temperatures and possible energy gaps at the band center are determined for the antiferromagnets CuWO₄ and Bi₂CuO₄ and for the singlet compounds (VO)₂P₂O₇ and CuGeO₃, agreeing satisfactorily with existing results, and new effects are also predicted.     

O2的化学吸附对2H—MoS2(0001)清洁表面和离子溅射表面电子结构的影响

利用低能N⁺(0.5keV)离子轻微轰击2H-MoS₂(0001)清洁表面,从UPS(HeⅠ,HeⅡ)得到d电子峰向E_F移动,价带顶出现明显的“肩膀”或带尾,它随轰击时间的增加而增强,同时使d_(z²)带变宽。UPS的结果表明,这种表面在室温下有明显的O₂吸附活性,O₂吸附后这个肩膀明显下降。结合XPS,AES和LEED的研究,我们认为这个“肩膀”态与次表面原子层的Mo原子的d电子的暴露和最外表面原子层s原子空位缺陷的产生有关。这些新的表面电子态与加氢脱硫(HDS)催化活性中心有密切的关系。 关键词：     

Correlation inequalities and the Kosterlitz-Thouless transition for anisotropic rotators

I give a proof of the Kosterlitz-Thouless transition for sufficiently anisotropic (J _zJ _x ^–1 =J _zJ _y ^–1 <2q ^–(JKT)^–J) two-dimensionalN-component rotators (N 3). The method is based on Wells' inequality and is related to mean field Gaussian inequalities.     

DNA Duplex Dynamics: NMR Relaxation Studies of a Decamer with UniformlyC-Labeled Purine Nucleotides

Dynamics in a DNA decamer duplex,d(CATTTGCATC) ·d(GATGCAAATG), were investigated via a detailed¹³C NMR relaxation study. Every 2′-deoxyadenosine and 2′-deoxyguanidine was chemically enriched with 15%¹³C and 98%¹⁵N isotopes. Six nuclear relaxation parameters [R(¹³C_z),R(¹H_z),R(2¹H_z¹³C_z),R(¹³C_x),R(2¹H_z¹³C_x) and steady-state¹³C{¹H} NOE] were measured at 600 MHz and three were measured at 500 MHz (¹H frequency) for the CH spin systems of sugar 1′, 3′, and 4′ as well as base 8 and 2 positions. A dependence of relaxation parameter values on chemical position was clearly observed; however, no sequence-specific variation was readily evident within our experimental error of ∼5–10%, except for 3′ and 5′ termini. It was demonstrated that the random 15%¹³C enrichment effectively suppressed both scalar and dipolar contributions of the neighboring carbons and protons on the relaxation parameters. To analyze dynamics via all observed relaxation parameters, full spectral density mapping (1992, J. W. Peng and G. Wagner,J. Magn. Reson.98, 308) and the “model-free” approach (1982, Lipari and Szabo,J. Am. Chem. Soc.104, 4546) were applied complementarily. A linear correlation between three spectral density values,J(ω_C),J(ω_H− ω_C), andJ(ω_H+ ω_C) was observed in plots containing all measured values, but not for the other spectral density terms includingJ(0). These linear correlations reflect the effect of overall motion and similar internal motions for each CH vector in the decamer. The correlations yielded two correlation times, 3–4 ns and 10–200 ps. One value, 3–4 ns, corresponds to the value of 3.3 ns obtained for the overall isotropic tumbling correlation time determined from analysis of¹³C T1/T2 ratios. The possibility of overall anisotropic tumbling was examined, but statistical analysis showed no advantage over the assumption of simple isotropic tumbling. Lack of correlations entailingJ(0) implies that a relatively slow chemical exchange contributes to yielding of effectiveJ_eff(0) values. Based on spectral density mapping and the T1/T2 ratio analysis, three basic assumptions were initially employed (and subsequently justified) for the model-free calculation: isotropic overall tumbling, one internal motion, and the presence of chemical exchange terms. Except for terminal residues, the order parameterS²and the corresponding fast internal motion correlation time were determined to be about 0.8 ± 0.1 and 20 ± 20 ps, respectively, for the various CH vectors. Only a few differences were observed between or within sugars and bases. The internal motion is very fast (ps–ns time scale) and its amplitude restricted; e.g., assuming a simple wobble-in-a-cone model, the internal motion is restricted to an angular amplitude of ±22.5° for each of the 1′, 3′, 4′, 2, and 8 positions in the purine nucleotides in the entire duplex.     

Weak exchange interactions in the heteronuclear crystal CuPr2(CCl3COO)8·6H2O

The new heteronuclear crystal CuPr₂(CCl₃COO)₈·6H₂O, constructed of chains containing copper and praseodymium atoms, has been synthesized and investigated by EPR at 9.3 GHz at temperatures ranging from room temperature down to 10 K. At temperatures T∼300–130 K, EPR spectra are observed which are characteristic of isolated polyhedra of copper ions with g _z=2.330±0.005, g _x,y =2.053±0.005, A _z=139×10⁻⁴ cm⁻¹, and A _x,y <26×10⁻⁴ cm⁻¹. At temperatures T<130 K a complex spectrum is observed, associated with the appearance of weak exchange interactions between the copper ions in the chain (J _Cu-CuΣS _i·S _i+1), comparable in magnitude with the hyperfine interactions J _Cu-Cu=0.015 cm⁻¹ at T=10 K. The magnitude of the exchange interaction decreases smoothly as the temperature is raised. It is conjectured that orbitals of the praseodymium ions participate in the process of indirect exchange between the copper ions. Fiz. Tverd. Tela (St. Petersburg) 41, 2154–2157 (December 1999)     

X-ray photoelectron spectroscopic studies of black silicon for solar cell

The black silicon has been produced by plasma immersion ion implantation (PIII) process. The microstructure and optical reflectance are characterized by field emission scanning electron microscope and spectrophotometer. Results show that the black silicon appears porous or needle-like microstructure with the average reflectance of 4.87% and 2.12%, respectively. The surface state is investigated by X-ray photoelectron spectroscopy (XPS) technique. The surface of the black silicon is composed of silicon, carbon, oxygen and fluorine element. The formation of Si_xO_yF_z in the surface of black silicon can be proved clearly by the O 1s, F 1s and Si 2p XPS spectra. The formation mechanism of the black silicon produced by PIII process can be obtained from XPS results. The porous or needle-like structure of the black silicon will be formed under the competition of SF_x⁺ (x ≤ 5) and F⁺ ions etching effect, Si_xO_yF_z passivation and ion bombardment.     

Dynamics and distribution of doped holes in the CuO2 plane of slightly doped antiferromagnetic YBa2(Cu1 ? zLiz)3O6 + x (x < 0.1) studied by Cu(1) NQR

Incidence of doped holes in the CuO₂ plane on the AF state was studied by Cu(1) nuclear quadrupole resonance (NQR) in slightly doped YBa₂(Cu_{1 − z} Li _z )₃O_{6 + x} compounds. Inhomogeneous distribution of doped holes in the plane was detected in the low temperature measurements of transverse (1/T ₂) and longitudinal (1/T ₁) relaxation rates. We establish that at lower T the holes motion slows down and we estimate that the holes localize finally in restricted regions (∼3 lattice constants) in the Coulomb potential of the Li+ ions. Also we compared the hole behavior in slightly doped YBa₂(Cu_{1 − z} Li _z )₃O_{6 + x} samples with that in slightly doped Y_{1 − y} Ca _y Ba₂Cu₃O₆. A stronger trapping potential of the in-plane Li⁺ impurities was concluded as compared to slightly doped Y_{1 − y} Ca _y Ba₂Cu₃O₆ compound with out-of-plane Ca²⁺ impurities.