Theoretical study of stereodynamics for the D'+DS(ν = 0,j = 0)→D'D+S abstraction reaction

Quasiclassical trajectory (QCT) calculations have been performed for the abstraction reaction, D' +DS(v = 0, j = 0)→D'D+S on a new LZHH potential energy surface (PES) of the adiabatic 3A' electronic state [Lü et al. 2012 J. Chem. Phys. 136 094308]. The collision energy effect on the integral cross section and product polarization are studied over a wide collision energy range from 0.1 to 2.0 eV. The cross sections calculated by the QCT procedure are in good accordance with previous quantum wave packet results. The three angular distribution functions, P(θ_r), P(φ_r), and P(θ_r,φ_r), together with the four commonly used polarization-dependent differential cross sections ((2π/σ)(ds₀₀/dω_t), (2π/σ)(ds₂₀/dω_t), (2π/σ)(ds₂₂₊/dω_t), (2π/σ)(ds_21-/dω_t)) are obtained to gain insight into the chemical stereodynamics of the title reaction. Influences of the collision energy on the product polarization are exhibited and discussed.     

运用R矩阵方法研究低能电子与NO_2分子的散射

基于静电-交换和密耦合两种模型,采用R矩阵方法,研究了低能电子与二氧化氮自由基分子的积分散射截面和动量迁移散射截面,包括弹性散射和从电子基态到电子激发态的非弹性散射.采用aug-cc-pVTZ基组进行靶分子结构优化和散射研究.在密耦合模型中,包含6个电子的最低三个占据轨道1b_2,1a_1,2a_1被冻结,其余17个电子自由运动在活化空间中,并给活化空间增加了2b_1和7a_1两个虚轨道.包含了所有垂直激发能小于20 eV的靶分子电子组态,得到了收敛的散射截面,并与最新理论和实验值进行了比较.当入射能量小于4 eV时,本文结果与实验值符合得更好,校正了以往部分理论结果在极低能量处过高的现象,表明关联效应对于极低能量散射是非常重要的.     

Classical and quantum molecular dynamics of cation in (CH3NH3)3 Sb2Br9 polycrystal as studied by 1H NMR.

¹H spin-lattice relaxation times and second moments were determined for polycrystalline (CH₃NH₃)₃Sb₂Br₉ sample in a wide range of temperature (5–200 K) at 24.6 and 55.2 MHz. ²H NMR spectra of (CD₃NH₃)₃Sb₂Br₉ were recorded between 5 K and room temperature. The relaxation time is interpreted as a result of motion of two different non-equivalent types of monomethylammonium cations occurring at the 2:1 proportion in a unit cell. Below 30 K, the relaxation processes via tunneling are suggested to dominate. Above 30 K, only classical behaviour of methylammonium cations is detected. Two monomethylammonium cations relax with the classical correlated C₃ reorientation and the rotational tunnelling mechanism, while the third cation exhibits only the classical correlated reorientation. The dynamic parameters of these motions have been determined.     

A Correlation Potential Method for Electron Scattering Total Cross Section Calculations on Several Diatomic and Polyatomic Molecules over Energy Range 10 ～ 5000 eV

A complex optical model potential correlated by the concept of bonded atom, which considers the overlapping effect of electron clouds between two atoms in a molecule, is firstly employed to calculate the total cross sections for electron scattering on several molecules (NH₃, H₂O, CH₄, CO, N₂, O₂, and C₂H₄) over the energy range 10～5000 eV using the additivity rule model at Hartree-Fock level. The difference between the bonded atom and the free one in states is that the overlapping effect of electron clouds of bonded atoms in a molecule is considered. The quantitative total cross sections are compared with the experimental data and with the other calculations wherever available and good agreement is obtained over the energy range 10～5000 eV. It is shown that the correlated calculations are much closer to the available experimental data than the uncorrelated ones at lower energies, especially below 500 eV. Therefore, considering the overlapping effect of electron clouds in the complex optical model potential could be helpful for the better accuracy of the total cross section calculations of electron scattering from molecules.     

Total Cross Sections for Electron Scattering on Polyatomic Molecules (CH4, CO2,NO2, and N2O) at 10 ～ 3000 eV

A new modified formulation of the Additivity Rule (AR) was proposed to calculate the total electron scattering cross sections for CH₄, CO₂, NO₂, and N₂O, considering the overlapping between atoms in molecules and the not fully transparency of the molecules. The present calculation covers the range of impact energy from 10 to 3000 eV. The results are compared with experimental data and other theories where available. The atoms are presented by spherical complex optical potential, which is composed of static, exchange, polarization, and absorption terms.     

The transition probability of DJ-F0 and hole-burning quantum efficiency in the SryBa1−yFCl0.5Br0.5:Sm system

We report the changes of the ⁵D_J-⁷F₀(J = 2, 1, 0) transition probability with composition y and its effect on the hole burning quantum efficiency in the Sr_yBa_1−yFCl_0.5Br_0.5:Sm²⁺ system. We observed that the ⁵D_J-⁷F₀ transition probability increases with the increase of Sr concentration. This result is attributed to the reduction of the energy separation between the ⁵D_J level and the 4f5d bands, which makes the electron wave functions of ⁵D_J states mix further with that of the 4f5d states. The dependence of the hole-burning quantum efficiency on the 5D_J-⁷F₀ transition probability was derived by the dynamical equations of the spectral hole burning of divalent samarium. Furthermore, the hole-burning experiments in SrFCl_0.5Br_0.5:Sm²⁺ and BaFCl_0.5:Sm²⁺ were performed under the same conditions. The experimental results present that the hole-burning quantum efficiency of SrFCl_0.5Br_0.5:Sm²⁺ is higher than that of BaFCl_0.5Br_0.5:Sm²⁺.     

Total Cross Sections for Electron Scattering from CF4, CF3H,CF2H2, and CFH3 Molecules in Energy Range from 100 to 3000 eV

The additivity rule has been employed to calculate the total cross sections for electron scattering by CF4,CF3 H, CF2 H2, and CFH3 molecules over an incident energy range from 100 to 3000 e V. Compared with other calculations and experimental data for CF4, excellent agreement has been obtained. Above 1000 eV, there are no experimental data for CF3H, CF2H2, and CFH3, so the present results can provide comparison and prediction for experimental research.     

Er3+在KPb2Br5晶体中的选择替位对上转换发光光谱的影响

通过高温固相法制备了不同Er³⁺掺杂浓度的KPb₂Br₅多晶粉末样品. 由980 nm半导体激光器激发下得到的上转换发射光谱显示, 当掺杂浓度为2.5 mol%时, 样品主要表现为530 nm 和550 nm上转换发射, 分别对应激发态²H_11/2和⁴S_3/2向基态⁴I_15/2的跃迁; 掺杂浓度增加到5 mol%时样品以490 nm上转换发射为主, 对应由激发态⁴F_7/2向⁴I_15/2的跃迁; 当掺杂浓度达到7.5 mol%时, 样品的上转换发射强度相比低浓度时大幅度下降, 主要以激发态⁴F_9/2 向基态⁴I_15/2跃迁的690 nm处发光为主. 利用第一性原理结合Judd-Ofelt理论讨论认为, Er³⁺ 离子优先替代Pb (1) 的位置, 随着浓度的提高, 部分Er³⁺ 离子会替代Pb (2) 格位上的离子, 不同晶格位置的Er³⁺ 离子所处的晶体场的对称性有所不同, 从而影响了发光中心不同能级的跃迁概率, 体现在上转换发光光谱的差异上. 蓝、绿区域的上转换发光在高浓度掺杂下显示了明显的浓度猝灭, 此时样品以红色上转换发光为主. 关键词： 2Br₅：Er³⁺')" href="#">KPb₂Br₅：Er³⁺ Judd-Ofelt理论 第一性原理 上转换发射     

新型固态照明用发光材料Ca3SiO4Br2:Eu2+的合成、结构与发光性能

制备了一种Eu2+掺杂的新型Ca3SiO4Br2蓝色发光材料,详细研究了其晶体结构组成.采用助熔剂法生长出Ca3SiO4Br2片状单晶,解析并证实该晶体为Ca3SiO4Br2,其结构基元中存在交替排列的Ca2SiO4和CaBr2层.荧光光谱测试表明:Ca3 SiO4Br2:Eu2+材料可被近紫外光( 300～ 430 ...     

Photoionization of CF4 in the VUV region

We present calculated results of photoionization cross sections and photoelectron angular distributions for ionization out of the five outermost valence orbitals of CF₄ for photon energies ranging from near threshold to 55 eV. The Schwinger variational iterative method, using an exact static-exchange plus a model correlation–polarization potential, is applied to obtain the continuum photoelectron orbitals. The quantitative agreement between our calculated results and the experimental data is fair. Moreover, our study is capable of identifying most structures seen in experimental results for both cross sections and asymmetry parameters.     

Stereodynamics study of the H′（^2S） ＋ NH（X^3∑-） 〉 N（4S） ＋ H2 reaction

The stereodynamics and reaction mechanism of the H′（^2S） ＋ NH （X^3∑^-） → N（^4S） ＋ H2 reaction are thoroughly studied at collision energies in the 0.1 eV-1.0 eV range using the quasiclassical trajectory （QCT） on the ground 4A″ potential energy surface （PES）. The distributions of vector correlations between products and reagents P（φr）, P（φr） and P（φr,φr） are presented and discussed. The results indicate that product rotational angular momentum j′ is not only aligned, but also oriented along the direction perpendicular to the scattering plane; further, the product H2 presents different rotational polarization behaviors for different collision energies. Furthermore, four polarization-dependent differential cross sections （PDDCSs） of the product He are also calculated at different collision energies. The reaction mechanism is analyzed based on the stereodynamics properties. It is found that the abstraction mechanism is appropriate for the title reaction.     

氢化铁的自旋极化效应及势能函数

B3LYP/6-311++g**水平上预测了FeH2及FeH稳定构型讨论了其自旋极化效应,并与实验结果进行了比较.结果表明其基态分别为FeH2(5A1)和FeH(4?),自旋态对构型和物理性质均有显著影响.FeH2具有C2v对称性.势能与核间距的关系用4参数Murrell-Sorbie函数进行拟合得到其分析势能函数.由此推导出力常数和光谱数据,并由多体项展式理论导出了基态FeH2分子的分析势能函数.用这个分析势能函数分析表明:H+FeH生成FeH2(C2v)分子通道存在一个4.68 eV深的势阱,易生成H—Fe—H络合物分子.反应Fe+H2→HFeH,?H=-0.08305 eV,是放热反应.     

BeCl_2分子的低能电子弹性散射研究

基于R矩阵理论方法,通过构建BeCl_2分子的静态交换势模型(SE),静态交换加极化势模型(SEP)和密耦合模型(CC),在0-10 eV能量范围内首次研究了低能电子与BeCl_2分子的散射动力学过程,预测了弹性散射积分截面,并在三种模型中分别发现一个来自B_(2u)和B_(3u)对称性贡献的势形共振态.讨论了这些共振态随着极化效应的变化,获得了收敛的截面和共振态结果.进一步使用POLYDCS程序首次计算了电子与BeCl_2分子的散射微分截面(DCS)以及动量转移截面(MTCS).当前研究结果将为天体物理和等离子体物理提供重要的截面数据.     

量子计算正三角形腔内的氢负离子光剥离截面

用传统量子力学方法研究了横截面为正三角形的腔内氢负离子光剥离, 得到了光剥离截面随能量变化的解析表达公式. 该公式还给出了剥离截面的阈值行为. 进一步研究发现, 当氢负离子处于正三角形一角附近时, 用量子力学方法得到的结果与氢负离子处于60°角域内时使用闭合轨道理论得到的结果一致.     

碱金属Li,Na,K,Rb,Cs,Fr的ns2S1/2,np2P1/2,3/2, nd2D3/2,5/2 和nf2F5/2,7/2 里德伯能级理论研究

本文在多通道量子数亏损理论(MQDT)框架下,利用相对论多通道理论(RMCT),分别在冻结实近似、 考虑Δl=-1的偶极极化效应、Δl=+1的偶极极化效应、Δl=± 1的偶极极化效应、伸缩模效应以及同时考虑偶极极化效应和伸缩模效应等不同层次近似下,系统地计算了碱金属Li, Na, K, Rb, Cs和Fr七个里德伯系列的能级,即ns²S_1/2, np²P_1/2, np²P_3/2, nd²D_3/2, nd²D_5/2, nf²F_5/2 和nf²F_7/2.计算结果表明,电子关联效应对碱金属原子的里德伯能级的影响很大.总的来说,偶极极化效应比伸缩模效应重要,而在偶极极化效应中, Δl = + 1的偶极极化效应比Δl = - 1的偶极极化效应重要.但对于Na的ns²S_1/2,(nd²D_3/2,nd²D_5/2)里德伯系列的能级,和Li的(np²P_1/2,np²P_3/2)里德伯系列的能级,是伸缩模效应比较重要.     

N2价轨道的精细电子动量谱学研究

在高分辨率（ΔE=08?eV,Δp≈01a.u.）高效率的第三代电子动量谱仪上获得了N₂价轨道的电离能谱和动量谱.通过对伴线结构的电子动量谱学（EMS）研究,得到了不同伴线结构的电子动量谱,另一方面也得到了伴线结构的强度.由伴线的电子动量分布形状判断出其跃迁的主要来源,并由实验测量的伴线结构强度确定了谱因子（极强度）的大小,通过对谱因子实验值与理论计算结果的比较检验了各种理论模型的精确度. 关键词： 氮分子 价轨道 电子动量谱 电子关联效应     

激发态Li原子和基态Ar原子的相互作用势及低能弹性碰撞

在MRCI+Q/ang-cc-PCVQZ+DK理论基础上对LiAr第一激发态(A²Π)的势能曲线进行了理论计算, 采用HFD(Hartree-Fock dispersion)解析势能函数对得到的势能曲线进行拟合, 并得到了相应的光谱常数, 计算结果与实验值和大部分理论计算值符合得很好. 通过求解核运动的薛定谔方程完整地获得了每个电子态下J=0时的振动能级E_v、转动惯量B_v和6 个离心畸变常数(D_v, H_v, L_v, M_v, N_v, O_v). 然后采用分波法研究了低温及极低温度下激发态Li原子和基态Ar原子沿LiAr相互作用势的弹性碰撞, 在1.0×10^{- 12} –3.45×10^-6 eV碰撞能区内通过数值计算得到了这一弹性碰撞的总截面和各分波截面, 讨论了各分波截面对总截面的影响. 结果表明: 在入射能量低于10^-9 eV时弹性散射的总截面值很大且几乎为一常数, 总弹性截面的形状主要由s分波决定, 但是随着碰撞能量的增加, s分波对总截面的贡献不断减少, 高阶分波对散射截面的贡献逐渐增大.     

基于4A"势能面研究C(3P)+NO(X2Π)→CO(X1Σ+)+N(4S)反应的立体动力学性质

运用准经典轨线方法(QCT), 基于Abrahamsson等构造的⁴A"势能面(Abrahamsson E Andersson S, Nyman G, Markovic N 2008 Phys. Chem. Chem. Phys. 10 4400), 在碰撞能为0.06 eV时, 对C(³P)+NO(X²Π )→CO(X¹Σ⁺)+N(⁴S)反应立体动力学性质进行了理论研究. 在考虑反应物NO转动和振动激发的条件下, 计算了质心坐标系下k-j'矢量(k与j'分别为反应物速度与产物角动量)相关的P(θ_r)分布和k-k'-j'矢量(k'为产物相对速度)相关的P(φ_r)分布. 此外还计算了该反应的三个极化微分截面(2π/σ)(dσ₀₀/dω_t), (2π/σ)(dσ₂₀/dω_t)以及(2π/σ)(dσ₂₂+dω_t). 计算结果表明转动和振动激发对产物取向影响较大而对定向影响较小; 对于三个极化微分截面, 转动激发的影响不大, 而振动激发的影响则较大.     

Interfacial properties of 2D WS2 on SiO2 substrate from X-ray photoelectron spectroscopy and first-principles calculations

Two-dimensional (2D) WS₂ films were deposited on SiO₂ wafers, and the related interfacial properties were investigated by high-resolution X-ray photoelectron spectroscopy (XPS) and first-principles calculations. Using the direct (indirect) method, the valence band offset (VBO) at monolayer WS₂/SiO₂ interface was found to be 3.97 eV (3.86 eV), and the conduction band offset (CBO) was 2.70 eV (2.81 eV). Furthermore, the VBO (CBO) at bulk WS₂/SiO₂ interface is found to be about 0.48 eV (0.33 eV) larger due to the interlayer orbital coupling and splitting of valence and conduction band edges. Therefore, the WS₂/SiO₂ heterostructure has a Type I energy-band alignment. The band offsets obtained experimentally and theoretically are consistent except the narrower theoretical bandgap of SiO₂. The theoretical calculations further reveal a binding energy of 75 meV per S atom and the totally separated partial density of states, indicating a weak interaction and negligible Fermi level pinning effect between WS₂ monolayer and SiO₂ surface. Our combined experimental and theoretical results provide proof of the sufficient VBOs and CBOs and weak interaction in 2D WS₂/SiO₂ heterostructures.     

A new intrinsic defect in amorphous SiO2: Twofold coordinated silicon

The well known optical absorption band at 5.03 eV (the “B₂ band”) and luminescence band at 4.3 eV in amorphous SiO₂ are due to singlet-to-singlet transitions, while the luminescence band at 2.65 eV - due to triplet-to-singlet transitions in a silicon-related intrinsic defect. This defect occurs both in the bulk and on the surface. Luminescence polarization data indicate C_2v symmetry. The most probable model for this center is a silicon atom with only two neighboring oxygens. Such defects form a separate class of valence alternation defects, characteristic for amorphous materials having atoms in tetrahedral coordination.