C78n离子的Jahn-Teller畸变和电子光谱

用INDO系列方法对C78n(D3、D3h、D?h)进行系统研究,表明C78(D3)比C78(D3h、D?h)稳定,与理论计算及实验结果一致;且随n绝对值增大,C78n总能量升高;C78n(D3、D3h、D?h)异构体的部分离子发生了Jahn-Teller畸变.以优化构型为基础,用INDO/SCI方法首次计算了C78n的电子光谱,对电子跃迁进行理论指认,讨论C78n光谱的特征吸收与C78相比发生红移的原因.     

T_(1u)h_gJahn-Teller系统:D_(3d)势阱中的频率分解与能级分裂

在C6 0 分子中 ,未被填充的最低电子态具有T1u对称性 ,因此 ,对中性的C6 0 而言 ,不论是通过分子内部激发 ,或是外部掺杂 ,都易被一个电子占据而形成Jahn Teller(JT)活跃电子态 .此态与五重简并的hg 声子态耦合 ,构成所谓的T1u hgJT系统 .在这一JT系统中 ,当只考虑电声的线性耦合时 ,其绝热势能面是一个槽形 .但在实际的系统中 ,二阶电声耦合是存在的 ,理论研究表明 ,原来的势槽将被这二阶非线性耦合弯曲成D3d或D5d 对称性的势阱 .声子振动态在阱中将显示各向异性效应 ,使得声子沿不同的方向有不同的振动频率 ,进而影响势阱中的能级分布、势阱间的重叠积分 ,以及整个系统的隧道能级分裂等 .对D3d势阱中各向异性效应进行了研究 ,利用幺正平移、 pik Pryce和标度变换等方法计算了系统势阱中的能级 ,以及阱中的振动频率 ,研究了势阱中的能级间隔以及微绕修正能量的变化 ,并由此导出了这些物理量在仅有线性耦合的势槽中变化的情形 .     

ZnS:Cr2+中局域晶格结构和自旋单态对零场分裂参量的贡献

在统一配体场耦合图像的基础上,构造了d⁴电子组态过渡金属离子在强场图像下包括所有自旋状态的210×210维完全能量矩阵.通过对角化完全能量矩阵,研究了Cr²⁺掺杂ZnS的局域晶格结构和Jahn-Teller能.理论计算结果与实验值符合非常好.同时,还研究了Cr²⁺掺杂ZnS后体系自旋单态对零场分裂参量的贡献.结果表明:自旋单态对二阶零场分裂参量D的贡献可以忽略,但是对于四阶零场分裂参量a和F的贡献却 关键词： 2+')" href="#">ZnS:Cr²⁺ 统一配体场耦合 自旋单态 Jahn-Teller能     

Influence of the Jahn-Teller distortion on magnetic ordering in TbMn_1-xFe_xO₃

The Jahn-Teller distortion plays an important role in determining the exchange interaction in rare-earth manganites.In this work we study the influence of the Jahn-Teller distortion on the magnetic structures of TbMn1-xFexO3(x = 0,0.02,0.05,0.10,and 0.20) single crystals in the basal MnO2 plane.The decrease in the quadruple splitting with the increasing Fe doping indicates the reduction of the Jahn-Teller distortion,which makes the nearest neighboring(NN) FM interaction dominant over the next nearest neighbor(NNN) AFM interaction.This alteration is favorable for the development of A-type AFM ordering instead of the spiral magnetic ordering,which collapses when x ≥ 0.05.The analysis of dielectric data indicates that the ferroelectricity is arising from the peculiar spiral magnetic ordering.     

Absolute frequency and isotope shift measurements of the cooling transition in singly ionized indium

We report greater than two orders of magnitude improvements in the absolute frequency and isotope shift measurements of the In⁺ 5s^{2 1}S₀ (F = 9/2)–5s5p ³P₁ (F = 11/2) transition near 230.6 nm. The laser-induced fluorescence from a single In⁺ in a radio-frequency trap is detected. The fourth-harmonic of a semiconductor laser is used as the light source. The absolute frequency is measured with the help of a frequency comb referenced to a Cs atomic clock. The resulting transition frequencies for isotopes ¹¹⁵In⁺ and ¹¹³In⁺ are measured to be 1 299 648 954.54(10) MHz and 1 299 649 585.36(16) MHz, respectively. The deduced cooling transition frequency difference is 630.82(19) MHz. By taking into account of the hyperfine interaction, the isotope shift is calculated to be 695.76(1.68) MHz.     

Structural Insights into Hysteretic Spin-Crossover in a Set of Iron(II)-2,6-bis(1H-Pyrazol-1-yl)Pyridine) Complexes

Bistable spin-crossover (SCO) complexes that undergo abrupt and hysteretic (ΔT_1/2) spin-state switching are desirable for molecule-based switching and memory applications. In this study, we report on structural facets governing hysteretic SCO in a set of iron(II)-2,6-bis(1H-pyrazol-1-yl)pyridine) (bpp) complexes – [Fe(bpp−COOEt)₂](X)₂ ⋅ CH₃NO₂ (X=ClO₄, 1 ; X=BF₄, 2 ). Stable spin-state switching – T_1/2=288 K; ΔT_1/2=62 K – is observed for 1 , whereas 2 undergoes above-room-temperature lattice-solvent content-dependent SCO – T_1/2=331 K; ΔT_1/2=43 K. Variable-temperature single-crystal X-ray diffraction studies of the complexes revealed pronounced molecular reorganizations – from the Jahn-Teller-distorted HS state to the less distorted LS state – and conformation switching of the ethyl group of the COOEt substituent upon SCO. Consequently, we propose that the large structural reorganizations rendered SCO hysteretic in 1 and 2 . Such insights shedding light on the molecular origin of thermal hysteresis might enable the design of technologically relevant molecule-based switching and memory elements.     

铜锌铝三元水滑石畸变结构和稳定性的理论研究

基于密度泛函理论,用CASTEP程序模块构建水滑石(CuxZn3-xAl-LDHs)周期性计算模型,进行模型的几何全优化,对各体系的结构参数、氢键、Mulliken电荷布居及结合能等进行分析,探讨体系中的Jahn-Teller效应和结构稳定性.计算结果表明,层板中Cu2+与Zn2+交错排列的构型比较稳定.随着层板上Cu2+取代Zn2+的量增多,晶胞对称性变差,但Cu2+的Jahn-Teller效应对中心Al3+的影响较小.CuxZn3-xAl-LDHs(x=0～3)体系中离子键逐渐变强,共价键逐渐变弱,体系整体上由共价型晶体向离子型晶体转变.体系中Jahn-Teller效应导致的畸变使主-客体作用力增强,其中静电作用力减弱,氢键强度变大,且氢键作用占优势.总体上,体系的结合能绝对值逐渐减小,稳定性降低,这对于合成含铜的LDHs材料具有理论指导意义.     

On the aspect of plane of appearance of Jahn-Teller and Renner-Teller intersections in tetra-atomic system—A case study with HCNO+

A search for configuration space with well-defined topological (Berry) phases corresponding to Jahn-Teller (JT) conical intersection (CI) and Renner-Teller (RT) parabolic intersection (PI) in the linear tetra-atomic molecular system on introduction of bending demonstrates the interesting aspect that these potential intersections may appear in the molecular plane as well as out of the molecular plane. While understanding this aspect is important for following the class of phenomena led by potential intersections, till date, studies on molecular systems, including pairs such as (C₂H₂⁺, HCNH) and (N₂H₂⁺, HBNH⁺), have not been able to clarify the issue. The present article includes calculation of nonadiabatic coupling terms involving four low-lying states of slightly bent HCNO⁺, a motivated choice of tetra-atomic with all four different atoms, to study this aspect associated with JT-CI and RT-PI in a slightly bent linear system. The plane of appearance of these effects has been advocated to be related to the electronic configuration of the concerned states of the molecular system.     

固相燃烧法制备去顶角八面体LiZn0.08Al0.01Mn1.91O4正极材料及其电化学性能

通过固相燃烧法快速合成了包含{111}、{100}和{110}晶面的单晶去顶角八面体形貌LiZn_0.08Al_0.01Mn_1.91O₄正极材料。结果表明,Zn-Al共掺促进了尖晶石型LiMn₂O₄材料的晶体发育和晶面择优生长,形成了单晶去顶角八面体形貌晶粒,有效抑制了Jahn-Teller效应,减缓了Mn溶解,增强了其晶体结构稳定性,显著提升了合成材料的电化学性能。LiZn_0.08Al_0.01Mn_1.91O₄在5C和10C下的首次放电比容量分别为92.6和76.5 mAh·g^-1,经过2 000次循环后的容量保持率分别为70.4%和74.8%。即使在15C高倍率下,仍有64.2 mAh·g^-1的首次放电比容量,循环800次后容量保持率达到82.2%。与LiZn_0.08Mn_1.92O₄相比,LiZn_0.08Al_0.01Mn_1.91O₄正极材料具有较大的Li+扩散系数(1.02×10^-11 cm²·s^-1)和较小的表观活化能(25.60 kJ·mol^-1),表明Zn-Al共掺和单晶形貌调控策略能够降低Li+在脱/嵌过程的能垒和增大Li+在电极材料中的扩散速率。     

锂电池正极材料Li1.06Mn0.8Cr0.14O2的水热合成及其光谱研究

采用水热方法合成了掺铬锂锰氧化合物, X射线衍射和Raman光谱分析结果表明, 所得材料为具有NaFeO2结构的晶体. 由等离子发射光谱(CIP)确定其组分为Li1.06Mn0.8Cr0.14O2. X射线光电子能谱(XPS)研究结果表明, 与未掺杂的LiMnO2相比, 所得材料中Mn的平均价态增加, 这将抑制因Mn3+离子的存在而产生的Jahn-Teller畸变, 有利于提高材料的电化学循环性能.