Exotic cluster structure in light neutron-rich nuclei

The cluster structure of C isotopes is investigated using a microscopic α+α+α+n+n… model based on the molecular orbit (MO) model. The stability of the linear chain of 3α with respect to the breathing mode and the bending mode for various neutron configurations is investigated. The combination of the valence neutrons in the π- and σ-orbits is promising to stabilize for these modes, and the excited states of ¹⁶C with the (3/2 _π ^- )²(1/2 _σ ^- )² configuration for the four valence neutrons are one of the most promising candidates for such structure. Furthermore, the equilateral-triangular shape of 3α surrounded by valence neutrons is suggested for ¹⁴C. The 3^-, 4^-, and 5^- members of this rotational band appear around the ¹⁰Be+α threshold, and these calculated states correspond to the experimentally observed 3^- state (9.80 MeV) and 4^- state (11.67 MeV). A positive-parity rotational band (0⁺, 2⁺, 4⁺) also arises around this threshold energy, and these results suggest that the picture of inversion doublet structure works also in neutron-rich nuclei.     

Formation of negative hydrogen ion in positronium-hydrogen collisions

The importance of the excited states of Positronium (Ps) in the formation cross sections (both differential and total) of the negative hydrogen ion (H^-) are investigated theoretically for the charge transfer reaction, Ps (n = 1, 2) + H ↦ e⁺ + H^- for a wide range of incident energies (e.g., threshold – 500 eV). The calculations are performed in the frame work of a qualitative model, the post collisional Coulomb modified eikonal approximation (CMEA). A comparative study is also made between the capture from ground and excited states of the Ps. The present CMEA model takes account of higher order effects which is essential for a rearrangement process where the first Born type approximation (Coulomb Born for the ionic case) is not supposed to be adequate. At low incident energies, the excited states of Ps (2s, 2p) are found to play a dominant role in the H^- formation cross sections. Significant deviations are noted between the present CMEA and the Coulomb Born (CBA) results even at very high incident energies (e.g., E_i = 500 eV), indicating the importance of higher order effects. At high incident energies the present CMEA differential cross section (DCS) exhibits a double peak structure which is totally absent in the CBA and could again be attributed to higher order effects.     

(SiO_2)_n~-(n≤7)团簇的密度泛函研究

采用密度泛函理论中的广义梯度近似对(SiO2)n-(n≤7)负离子团簇的几何构型进行了优化,并对能量和频率进行了计算.通过对计算结果的分析发现,与近邻尺寸的团簇比较,(SiO2)4-团簇最低能量结构更加稳定;(SiO2)n-(n≥4)团簇的最低能量结构是以(SiO2)4-为基础结构,具有一定的生长规律.     

Electron affinities of the bromine oxides BrOn,n = 1-4

Bromine oxides are of significant interest due to their importance in atmospheric chemistry. Density functional theory (DFT) methods have been used in conjunction with a DZP++ (double-ζ plus polarization with diffuse functions) basis set to study the molecular geometries and total energies of BrOn and BrO^- _n (n = 1-4). The adiabatic electron affinity (EA_ad), the vertical electron affinity (EA_vert) of the bromine oxide and the vertical detachment energy (VDE) of each anion are reported. Harmonic vibrational frequencies and zero point energies are also reported. Five different DFT methods were employed for comparison. Among these, the BHLYP method predicts the geometries and the vibrational frequencies in best agreement with available experimental data, while the the other methods do better in predicting the limited number of energetic quantities determined observationally. The predicted adiabatic electron affinities are 2.38 eV (BrO, experiment 2.35 eV), 2.36 eV (BrO₂), 3.35 eV (BrOO), 4.32 eV (BrO₃), 2.91 eV (BrOOO) and 5.28 eV (BrO₄). The electronic ground state of BrOO^- is a triplet (³A^") state. Predicted Br–;O bond distances range from 1.61 (BrO₃) to more than 2 Å for Br...O₂ for the neutral molecules; and from 1.61 Å for BrO^- to 1.82 Å for BrO^- to more than 2 Å for Br^-...O₃ among the anions. The BrOO isomer (C_s symmetry) is predicted to lie 17–18 kcal mol^-1 below the C_2v symmetry OBrO structure. The asymmetric ³A^" anion BrOO^- analogously lies below OBrO^-, in this case by 40–41 kcalmol_-1. BrOOO (C_s symmetry) is predicted to lie 42-45 kcalmol-1 below the symmetric C_3v BrO structure. Finally the asymmetric BrOOO- anion (C₁ symmetry) is predicted to lie 10-13kcal mol-1 below symmetric C_3v BrO^- ₃.     

Cross-sections for the formation of isomeric pair Ge through (n, 2n), (n, p) and (n, α) reactions measured over 13.73 MeV to 14.77 MeV and calculated from near threshold to 20 MeV neutron energies

The cross-sections for formation of isomeric pair, ⁷⁵Ge^m(σ_m) and ⁷⁵Ge^g(σ_g), through ⁷⁶Ge(n, 2n), ⁷⁵As(n, p) and ⁷⁸Se(n, α) reactions were measured at 13.73 MeV, 14.42 MeV and 14.77 MeV neutrons and also estimated using EMPIRE-II and TALYS codes over neutron energies from near threshold to 20 MeV. For each (n, 2n), (n, p) and (n, α) reaction, the cross-section initially increases with neutron energy, but starts decreasing as the neutron energy exceeds the respective threshold of (n, 3n), (n, pn) and (n, αn) reactions. The higher values of σ_m relative to σ_g reveal that the transitions of the excited ⁷⁵Ge from higher energy levels to metastable state (7⁺/2) are favored as compared to unstable ground state (1⁻/2). The present values of cross sections for formation of ⁷⁵Ge^m,g through (n, 2n) and (n, α) reactions are lower, and that of (n, p) reaction are higher compared to most of the corresponding literature cross-sections.     

GanN－m阴离子团簇的结构及稳定性的研究

利用密度泛函理论(DFT)对Ga_nN^-(n=2—8)和Ga_nN^-₂ (n=1—7)阴离子团簇的结构及稳定性进行了研究.在B3LYP/6-31G^*水平上进行了结构优化和频率分析，得到了Ga_nN^-(n=2—8)和Ga_nN^-₂(n=1—7)阴离子团簇的基态结构.在这些团簇中，原子总数小于等于6的团簇的几何结构为平面结构，原子总数大于6的团簇的几何结构为立体结构；在所研究的团簇中，Ga₄N^-，Ga₆N^-,Ga₄N^-₂和Ga₅N^-₂的基态结构较稳定. 关键词： nN^-_m团簇')" href="#">Ga_nN^-_m团簇 密度泛函理论(DFT) 几何结构     

The threshold photoproduction of π0 on nucleons and on few-nucleon systems

The absolute value of the π⁰ photoproduction cross section on the proton recently measured near threshold enables to reanalyze previous data collected on ²H, ³He, and ⁴He relatively to the proton. Absolute cross sections are presented for these nuclei in the energy region extending up to 10 MeV above threshold. The threshold s-wave amplitudes for ²H and ³He thus obtained are discussed in relation with the neutron threshold amplitude E^(nπ0)₀₊ value.     

Photodetachment of H- near an elastic surface in a magnetic field

This paper investigates the photodetachment of the negative hydrogen ion H near an elastic wall in a magnetic field.The magnetic field confines the perpendicular motion of the electron,which results in a real three-dimensional well for the detached electron.The analytical formulas for the cross section of the photodetachment in the threedimensional quantum well are derived based on both the quantum approach and closed-orbit theory.The magnetic field and the elastic surface lead to two completely different modulations to the cross section of the photodetachment.The oscillation amplitude depends on the strength of the magnetic field,the ion-wall distance and the photon polarization as well.Specially,for the circularly polarized photon-induced photodetachment,the cross sections display a suppressed(E E th) 1/2 threshold law with energy E in the vicinity above Landau energy E th,contrasting with the(E E th) 1/2 threshold law in the presence of only the magnetic field.The semiclassical calculation fits the quantum result quite well,although there are still small deviations.The difference is attributed to the failure of semiclassical mechanics.     

高离化态类镍离子电子碰撞激发过程的相对论扭曲波理论研究

利用相对论扭曲波方法和新发展的研究电子碰撞激发过程的计算程序REIE06,系统计算了电子碰撞激发高离化态类镍Gd³⁶⁺和Rn⁵⁸⁺—U⁶⁴⁺(Z=86—92)离子从基态到4l(l=s,p,d,f)次壳层精细结构能级的碰撞强度和截面.研究了随等电子系列变化时,从基态到与X射线激光有关的3d⁹4p和3d⁹4d激发态能级的电子碰撞激发截面随Z的变化,讨论了强的组态相互作用对高离化态类镍离子截面的影响.通过对Gd³⁶⁺离子涉及X射线激光跃迁的相关能级电子碰撞激发速率系数的计算,分析了等离子体中电子温度对碰撞过程的影响.同时,目前部分计算结果与以往的理论结果进行了比较,得到了很好的一致性. 关键词： 电子碰撞激发 相对论扭曲波方法 高离化态类镍离子     

Spectroscopic characteristic and energy levels of Cr in Cr:KAl(MoO4)2 crystal

This paper reports polarized spectral properties and energy levels of Cr³⁺ in KAl(MoO₄)₂ crystal. The absorption and emission cross sections are estimated as 3.72×10^-20 cm² at 669 nm and 2.74×10^-20 cm^-2 at 823 nm for σ-polarization, respectively. The energy levels of Cr³⁺ ion in KAl(MoO₄)₂ crystal were calculated based on the Tanabe-Sugano theory. It is suggested that Cr³⁺ ions occupy at an intermediate crystal field site in Cr³⁺:KAl(MoO₄)₂.     

钪原子的自电离里德伯能级3d4s(1D2)nf2 D3/2,3d4s(1D2)nf2 F5/2和3d4s(1D2)np2 D3/2<

在多通道量子亏损理论框架下,利用相对论多通道理论,分别在冻结实近似和考虑偶极极化下计算钪原子的J^π=(3/2)^-,(5/2)^-的三个收敛于 3d4s(¹D₂)的自电离里德伯系列的能级.对3d4s(¹D₂)np²D_3/2和3d4s(^{1 关键词： 相对论多通道理论 多通道量子亏损理论 电子-电子关联 自电离里德伯系列}     

Chemi-ionization and spin exchange upon collisions of metastable helium atoms with potassium atoms in the ground state

The spin exchange and chemi-ionization cross sections have been calculated for the metastable helium atom-potassium atom system in the ground state. The data on the spin exchange cross section in the system He(2³ S ₁)-K(4² S _1/2) have been obtained for the first time. The cross sections were calculated for the collision energies ranging from 2 × 10^?4 to 60 × 10^?4 au The chemi-ionization cross sections obtained have been compared with the data in the literature.     

Chemical effects of nuclear transformations in mixed crystals. 13. chemical effects of the 79Br(n, γ)80mBr nuclear reaction in K2OsBr6-K2OsCl6, K2ReBr6-K2ReCl6, and K2OsBr6-K2SnCl6 mixed crystals [1]

The solid-state reactions occurring during the moderation of (n, γ) produced hot ^80mBr were studied in K₂OsBr₆-K₂OsCl₆, K₂ReBr₆-K₂ReCl₆, and K₂OsBr₆-K₂SnCl₆ mixed crystals. The formation of the main reaction products M^80mBrBr5/2-, M^80mBrCl5/2- (M = Re, Os), Os^80mBrBr₄Cl^2-, and ^80mBr^- is attributed to the following reaction channels: (1) primary retention or bond-preservation because of insufficient recoil energy, (2) billiard-ball reaction (substitution or replacement of ligands by recoil ^80mBr), (3) substitution as in (2) but formation of an additional ligand vacancy which is filled by an adjacent halide ion, and (4) capture of ^80mBr at interstitial vacancies. From the experimental results the contributions of these reaction channels were evaluated quantitatively.     

Single α-particle orbits and Bose-Einstein condensation in <Superscript>12</Superscript>C

Bosonic properties of α particles such as single-α orbits and occupation numbers in J^π = 0⁺, 2⁺, 1^- and 3^- states of ¹²C around the 3α threshold are investigated with the semi-microscopic 3α cluster model. As in other studies, we found that the 0⁺₂ (2⁺₂) state has dilute-3α-condensate-like structure in which the α particle is occupied in the single S (D) orbit with about 70% (80%) probability. The radial behaviors of the single-α orbits as well as the occupation numbers are discussed in detail in comparison with those for the 0⁺₁ and 2⁺₁ states together with the 1^-₁ and 3^-₁ states.     

Formation of higher-order fullerene dianions in collisions with Na atoms

We have measured electron capture cross sections in collisions between higher order fullerene anions C_n ^- (n=76, 78, 82, 84, 86, 90 and 96) and Na atoms. The ions were produced in an electrospray ion source (ESI) and accelerated to an energy of 50 keV. The measured cross section for dianion formation is three times larger for C₉₆ than that for C₆₀. The latter cross section was earlier found to be 36 ?². The dramatic increase of the cross section with fullerene size is explained by means of the curve crossing model for electron transfer.     

硅中四空位扩展的Koster-Slater模型

本文用扩展的Koster-Slater模型计算了硅中V₄^-未配对电子的对称化波函数,用算得的波函数计算了缺陷电子局域在最近邻每个原子上的η²及其s特征α²,和超精细相互作用常数,确定V₄^-处于深能级为0.78eV的A₁对称态,给出与现有实验值相符合的结果。并指出,V₄^-的单个悬挂键上的η²比其它具有单个悬挂键的缺陷小,是由于V₄^-的势分布向一侧有较大偏重所致。 关键词：     

Odd autoionizing 2p<Subscript>1/2</Subscript><Superscript>5</Superscript>n(s<Superscript>′</Superscript>/d<Superscript>′</Superscript>) resonances of Ne excited from the 2p<Superscript>5</Superscript>3p[K]<Subscript>J</Subscript> states

Absolute photoionization cross sections for Ne atoms in the excited levels (Paschen notation ) were calculated at near threshold energies within the configuration interaction Pauli-Fock approach including core polarization. The computed spectra and the lineshape parameters of the odd parity 2p_1/2 ⁵ns^′/d^′ autoionizing resonances are found to be in good agreement with high resolution laser spectroscopic results. Guided by the theoretical results, improved analyses of the measured spectra by superimposed Fano-type profiles were achieved. Theoretical predictions are presented for resonances which have not yet been studied experimentally. In addition, we report the absolute partial photoionization cross sections for the ²P_3/2 and ²P_1/2 channel at photoelectron energies up to 7 eV. Except for the highest lying 2p₁(¹S₀) level, these cross sections monotonically decrease with energy (as reported earlier in single-electron calculations for the Ne(2p⁵3p) configuration) with branching ratios which essentially reflect the core composition of the 2p_x levels. For the 2p₁ level the resonance structure and the partial cross sections are strongly influenced by a Cooper-Seaton minimum in the d_3/2 ^′ channel,located just above the ²P_1/2 ionization limit.     

New data for the 197Au(γ, nX) and 197Au(γ, 2nX) reaction cross sections

The results from experimental and theoretical studies of the total and partial cross sections of photoneutron reactions on the ¹⁹⁷Au isotope were analyzed. The cross sections for reactions σ(γ, nX) = σ(γ, n) + σ(γ, np) + … + σ(γ, 2nX) = σ(γ, 2n) + σ(γ, 2np) + … were evaluated in the energy range 7 ≤ E _γ ≤ 30 MeV using an approach free of the shortcomings of experimental photoneutron multiplicity sorting methods. The total photoneutron reaction cross sections σ^exp(γ, xn) = σ^exp(γ, nX) + 2σ^exp(γ, 2nX) + … = σ^exp(γ, n) + σ^exp(γ, np) + 2σ^exp(γ, 2n) + 2σ^exp(γ, 2np) + … were used as the initial experimental data. The contributions from the cross sections σ(γ, nX) and σ(γ, 2nX) to the cross sections σ^exp(γ, xn) were separated using the multiplicity transition functions F ₁ ^theor = σ^theor(γ, 1nX)/σ^theor(γ, xn) and F ₂ ^theor = σ^theor(γ, 2nX)/σ^theor(γ, xn), calculated within an updated version of the pre-equilibrium model of photonuclear reactions. New evaluated data for both partial reaction cross sections, i.e., σ^eval (γ, 1nX) = F ₁ ^theorσ^exp(γ, xn) and σ^eval(γ, 2nX) = F ₂ ^theorσ^exp(γ, xn), were obtained. The cross sections σeval(γ, nX) and σ^eval.(γ, 2nX) evaluated using the theoretically calculated functions F _1,2^theor are consistent with the Livermore data, but substantially contradict the Saclay data.     

The nuclear fusion in the muonic molecule ddμ and the charge symmetry violation in the low energy dd interaction

The rate λ_f = 1.0 × 10⁹ s^?1 of the nuclear fusion in the ddμ molecule is calculated. It is shown that the ratio of the neutron to the proton yield equals the ratio of the p-wave cross sections of the d(d,n)³ He and d(d,p)t reactions near the dd threshold.     

Influence of lithium phosphate concentration and temperature on the electrical conduction of (76V2O5-24P2O5)1−X (Li3PO4)X glasses

Characterization of the (76V₂O₅-24P₂O₅)_1−X (Li₃PO₅)_X, where X=0.0,0.01,0.02,0.10 and 0.15, glass has been done using X-ray diffraction and differential thermal analysis (DTA). The dc conductivity of the glass samples was studied over a temperature range from 300 to 593 K. The temperature dependence of dc conductivity shows two regions. One at relatively high temperature range, above θ_D/2, and the other at relatively low temperature range, below θ_D/2. The I-V characteristics of the glasses have been studied as a function of both temperature and Li₃PO₄ content. The I-V characteristics exhibits threshold switching with differential negative resistance. It's found that both the threshold voltage (V_th) and threshold current (I_th) are dependent on the temperature and lithium phosphate concentration.