Local spin density in the Cr(7)Ni antiferromagnetic molecular ring and (53)Cr-NMR

We present (53)Cr-NMR spectra collected at low temperature in a single crystal of the heterometallic antiferromagnetic (AF) ring Cr(7)Ni in the S?=?1/2 ground state with the aim of establishing the distribution of the local electronic moment in the ring. Due to the poor S/N we observed only one signal which is ascribed to three almost equivalent (53)Cr nuclei in the ring. The calculated spin density in Cr(7)Ni in the ground state, with the applied magnetic field both parallel and perpendicular to the plane of the ring, turns out to be AF staggered with the greatest component of the local spin ?s? for the Cr(3+) ions next to the Ni(2+) ion. The (53)Cr-NMR frequency was found to be in good agreement with the local spin density calculated theoretically by assuming a core polarization field of H(cp)?=-?11?T/μ(B) for both orientations, close to the value found previously in Cr(7)Cd. The observed orientation dependence of the local spin moments is well reproduced by the theoretical calculation and evidences the importance of single-ion and dipolar anisotropies.     

密度泛函理论研究SiCmN团簇

用密度泛函理论(DFT)的B3LYP/6-311G*方法,对SiCmN(m=1-7)团簇的几何构型、振动频率和基态能量等性质进行了研究,讨论了化学键的特征和热力学稳定性。振动频率和振动强度被用来判断体系的基态结构。结果表明,m=1~5的团簇为线状结构,m=6、7的团簇为环状结构。m增大过程中,线状团簇自旋多重度均为2,而环状团簇出现2、4和6自旋多重度。能量的二次差分值表明m为奇数的团簇比m为偶数的更为稳定。     

密度泛函理论研究SiCmN团簇

用密度泛函理论(DFT)的B3LYP/6-311G*方法,对SiCmN(m=1-7)团簇的几何构型、振动频率和基态能量等性质进行了研究,讨论了化学键的特征和热力学稳定性。振动频率和振动强度被用来判断体系的基态结构。结果表明,m=1~5的团簇为线状结构,m=6、7的团簇为环状结构。m增大过程中,线状团簇自旋多重度均为2,而环状团簇出现2、4和6自旋多重度。能量的二次差分值表明m为奇数的团簇比m为偶数的更为稳定。     

The phase diagram and hidden order for generalized spin ladders

We investigate the phase diagram of antiferromagnetic spin ladders with additional exchange interactions on diagonal bonds by variational and numerical methods. These generalized spin ladders interpolate smoothly between the [Formula: see text] chain with competing nn and nnn interactions, the [Formula: see text] chain with alternating exchange and the antiferromagnetic (AF) S = 1 chain. The Majumdar - Ghosh ground states are formulated as matrix product states and are shown to exhibit the same type of hidden order as the AF S = 1 chain. Generalized matrix product states are used for a variational calculation of the ground state energy and the spin and string correlation functions. Numerical (Lanczos) calculations of the energies of the ground state and of the low-lying excited states are performed, and compare reasonably with the variational approach. Our results support the hypothesis that the dimer and Majumdar - Ghosh points are in the same phase as the AF S = 1 chain.     

YAG∶Cr3+ 晶体精细光谱结构研究

采用不同的晶体畸变模型，利用CDM(complete diagonalization method)方法对YAG∶Cr3+ 晶体的EPR参量进行了系统研究.通过计算结果对晶格畸变模型进行了分析.结果表明,在三角对称下，对杂质离子电荷与中心离子电荷相等的情况，不适合用杂质离子沿C3轴位移的模型来研究晶体的局域结构，而且由于基态和第一激发态的零场分裂都对局域结构微变非常敏感，因此仅由基态零场分裂来确定晶格局域结构是不可靠的.同时结果表明，Cr3+ 离子进入YAG晶体后，产生了Δθ=1.88°的三角畸变.从而成功统一地解释了YAG∶Cr3+ 晶体的EPR参量和精细光谱结构.     

Determination of the excited state structure of 7-azaindole using a Franck-Condon analysis

The change in structure of 7-azaindole upon electronic excitation was determined by a Franck-Condon analysis of the intensities in the fluorescence emission spectra obtained via excitation of six different vibronic bands. A total of 107 emission band intensities were fit, together with the changes in the rotational constants of four 7-azaindole isotopomers. The geometry change of the ring framework upon electronic excitation from the electronic ground state to the ¹L_b state (ππ*) can be described by an overall expansion of the pyridine ring of 7-azaindole, with minor changes of the pyrrole ring. The resulting geometry changes are interpreted on the basis of ab initio calculations.     

GaAs中Cr2+离子的发光及杨—泰勒效应

在各向同性压力下,观察到77°K时n—GaAs样品中Cr2+离子的光致发光。这个光谱带是由Cr2+离子的激发态5E到基态5T2的跃迁所致。由于Cr2+离子在晶体场中有较强的杨一泰勒效应,时发光光谱产生影响。本文考虑静态杨一泰勒效应计算了发射光潴,估计了杨一泰勒能量,并与实验结果相比较。     

Pb掺杂对Cd_2Ru_2O_7反常金属态的调控

具有烧绿石结构的Cd_2Ru_2O_7在形成长程反铁磁序的同时进入反常的金属态.采用高压高温方法制备了一系列Pb掺杂的Cd_(2-x)Pb_xRu_2O_7(0≤x≤2)多晶样品,并系统研究了其晶体结构和电阻率、磁化率、热电势等物理性质.尽管Pb_2Ru_2O_7是泡利顺磁金属,但少量Pb~(2+)掺杂的样品Cd1.8Pb0.2Ru2O7却呈现出明显的金属-绝缘体转变,与施加静水压和少量Ca~(2+)掺杂的效果类似.通过与类似的烧绿石Ru~(5+)氧化物进行对比,提出Cd_2Ru_2O_7中的Ru~(5+)-4d~3电子态恰好处于巡游到局域过渡的区域,少量Pb~(2+)掺杂造成的晶格无序增强了电子的局域性,使得形成反铁磁序的同时伴随出现了金属-绝缘体转变.这表明具有烧绿石结构的Ru~(5+)氧化物是研究巡游-局域电子转变的理想材料体系.     

The rotational spectrum of 2-indanone

The rotational spectrum of 2-indanone has been analysed in the 26.5-40 GHz frequency region. The ground state, the first five excited states of the five-membered ring bending mode and the first excited state of the ring twisting and butterfly modes have been assigned and analysed. From the ground state inertial defect and the variation of the rotational parameters with the ring bending quantum number a strictly planar C2v equilibrium conformation has been established. A one-dimensional potential function of the quadratic-quartic type V(X) = 3.3(7) (X4 + 11.66(15)X2)cm-1 has been derived for the bending vibration.     

Ce^3＋离子敏化Eu^3＋：Cr^3＋：Sm^3＋：YAG外延层的荧光现象

对Ce^3 :Eu^3 :Cr^3 :Sm^3 :YAG外延层中的荧光敏经现象进行了报道和分析，在较高浓度的Ce^3 离子掺杂时，外处层在蓝色、绿色波段出现了新的荧光谱线，可解释为在Ce^3 离子每化作用下，Eu^3 离子产生了由高位激发态能级^5Di(i=1,2,3）直接到基态能级^7Fj(j=0,1,2,3）的辐射跃迁过程，并且这种Ce^3 :Eu^3 :Cr^3 :Sm^3 :YAG外延层还是一种新颖的白色单晶荧光材料。     

Molecular dynamics and information on possible sites of interaction of intramyocellular metabolites in vivo from resolved dipolar couplings in localized 1H NMR spectra

Proton NMR resonances of the endogenous metabolites creatine and phosphocreatine ((P)Cr), taurine (Tau), and carnosine (Cs, beta-alanyl-L-histidine) were studied with regard to residual dipolar couplings and molecular mobility. We present an analysis of the direct 1H-1H interaction that provides information on motional reorientation of subgroups in these molecules in vivo. For this purpose, localized 1H NMR experiments were performed on m. gastrocnemius of healthy volunteers using a 1.5-T clinical whole-body MR scanner. We evaluated the observable dipolar coupling strength SD0 (S=order parameter) of the (P)Cr-methyl triplet and the Tau-methylene doublet by means of the apparent line splitting. These were compared to the dipolar coupling strength of the (P)Cr-methylene doublet. In contrast to the aliphatic protons of (P)Cr and Tau, the aromatic H2 (delta=8 ppm) and H4 (delta=7 ppm) protons of the imidazole ring of Cs exhibit second-order spectra at 1.5 T. This effect is the consequence of incomplete transition from Zeeman to Paschen-Back regime and allows a determination of SD0 from H2 and H4 of Cs as an alternative to evaluating the multiplet splitting which can be measured directly in high-resolution 1H NMR spectra. Experimental data showed striking differences in the mobility of the metabolites when the dipolar coupling constant D0 (calculated with the internuclear distance known from molecular geometry in the case of complete absence of molecular dynamics and motion) is used for comparison. The aliphatic signals involve very small order parameters S approximately (1.4-3) x 10(-4) indicating rapid reorientation of the corresponding subgroups in these metabolites. In contrast, analysis of the Cs resonances yielded S approximately (113-137) x 10(-4). Thus, the immobilization of the Cs imidazole ring owing to an anisotropic cellular substructure in human m. gastrocnemius is much more effective than for (P)Cr and Tau subgroups. Furthermore, 1H NMR experiments on aqueous model solutions of histidine and N-acetyl-L-aspartate (NAA) enabled the assignment of an additional signal component at delta=8 ppm of Cs in vivo to the amide group at the peptide bond. The visibility of this proton could result from hydrogen bonding which would agree with the anticipated stronger motional restriction of Cs. Referring to the observation that all dipolar-coupled multiplets resolved in localized in vivo 1H NMR spectra of human m. gastrocnemius collapse simultaneously when the fibre structure is tilted towards the magic angle (theta; approximately 55 degrees), a common model for molecular confinement in muscle tissue is proposed on the basis of an interaction of the studied metabolites with myocellular membrane phospholipids.     

ⅡB族金属dmit,dmid配合物的傅里叶拉曼光谱研究

通过改变配体结构、改变金属离子等方法研究了ⅡB族金属不对称二硫纶配合物[Me4N]2[MLn(SPh)2](M=Zn,CA;L1=dmit=1,3-二硫盐-4,5-二硫醇盐-2-硫酮盐,L2=dmid=1,3-二硫盐-4,5-二硫醇盐-2-酮盐)和[Bu4N]2[Zn(dmit)2]的固体粉末傅里叶拉曼(FT-Raman)光谱,并对它们进行了逐一比较标识。当配合物中dmit^2-被dmid^2-取代时会使1420cm^-1处C-C峰蓝移38cm^-1。左右;在990cm^-1处的吸收为五元杂环吸收峰,当Zn^2 被Cd^2 取代、dmit^2-被dmid^2-取代后,分别红移11和7cm^-1。在463cm^-1左右以及在300cm^-1左右的谱峰分别为配体dmit^2-或dmid^2-中S2C与CS2骨架上的S-C-S的伸缩振动和变形振动,同样随着dmit^2-被PhS^-取代、Zn^2 被Cd^2 取代而分别红移,但是dmid^2-取代dmit^2-时却使此峰蓝移。配合物中的Cd-S有两处振动峰,一处为硫酚的硫与Cd键的峰,另一处为dmit^2-或dmid^2-上的硫与CA键的峰,分别为180和140cm^-1左右。Zn-S振动峰同样有两种,硫酚的硫与Zn键的峰和dmit^2-或dmid^2-上的硫与Zn键的峰,它们分别在193和155cm^-1左右。     

水体中铬、镉和铅的X射线荧光光谱同时快速分析方法研究

以氢氧化钠和硫化钠为沉淀剂采用共沉淀法同时富集水体中的Cr,Cd和Pb,通过对Cr(OH)₃,Cd(OH)₂和PbS沉淀均匀悬浮液抽滤以制成Cr,Cd和Pb均匀分布的薄膜样品并进行能量色散XRF光谱测量,以实现水体中Cr,Cd和Pb的同时快速分析与检测。研究了富集过程中的反应时间和反应物摩尔比对薄膜样品XRF光谱强度的影响,确定了富集过程的最佳反应条件为沉淀反应时间为5 min,OH-与Cr3+的最佳摩尔比为5.0,OH-与Cd2+的最佳摩尔比为5.0,S2-与Pb2+的最佳摩尔比为2;对富集后不同浓度的薄膜样品进行了均匀性检验,富集区域6个不同位置荧光强度的相对标准偏差均小于4.8%,说明富集后的薄膜样品具有较好的均匀性;将不同浓度薄膜样品的理论浓度值与ICP-MS方法测得的浓度值进行对比分析,验证了该富集方法对水样中Cr,Cd和Pb的富集率均能达到90%以上;根据薄膜样品的荧光强度与ICP-MS测得的浓度值,建立了基于该富集方法的水体中Cr,Cd和Pb的X射线荧光光谱定量分析方法,Cr,Cd和Pb校准曲线的线性相关系数分别为0.997 3,0.995 0和0.999 8,当实际采集水样体积为50 mL时,Cr,Cd和Pb的检出限分别为7.4,29.6和8.5 μg·L-1,均低于《污水综合排放标准 GB 8978-1996》中Cr,Cd和Pb的最高允许排放浓度,因此该方法能够实现工业生产及生活排放污水中Cr,Cd和Pb的同时快速分析与检测。该研究为基于X射线荧光光谱法的水体多种重金属同时快速在线监测提供依据。     

Sr原子自电离态的电场效应

用多步激发的方法,将Sr原子从基态5s~2经价态4α~(-2)激发至(4d_(3/2)np,n_f)J=1和(4d_(5/2)np,nf)J=1自电离系列,观察其在外电场0～5kV/cm内的光谱.对所观察到的n=12,13,14附近的斯塔克谱图进行了分析与讨论.     

X-ray resonant magnetic scattering by Fe/Cr superlattices

We have studied the structural and magnetic properties of an antiferromagnetically (AF) coupled Fe/Cr superlattice by means of soft x-ray resonant magnetic scattering. Strong and purely magnetic Bragg peaks are observed at the half-order positions in reciprocal space parallel to the [001] growth direction and in between the structural Bragg reflections from the superlattice periodicity. The magnetic hysteresis loops measured at the first-order and at the half-order Bragg peaks clearly demonstrate the strong AF coupling of the Fe/Cr multilayer. Transverse scans and off-specular reflectivity measurements confirm an AF domain structure of the superlattice in remanence with large perpendicular correlation. In addition, the transverse scan of the half-order Bragg peak exhibits a Lorentzian line shape at zero field, which diminishes in higher fields, indicative of a remanent multidomain state approaching a single-domain state towards saturation.     

Molecular engineering of antiferromagnetic rings for quantum computation

The substitution of one metal ion in a Cr-based molecular ring with dominant antiferromagnetic couplings allows the engineering of its level structure and ground-state degeneracy. Here we characterize a Cr7Ni molecular ring by means of low-temperature specific-heat and torque-magnetometry measurements, thus determining the microscopic parameters of the corresponding spin Hamiltonian. The energy spectrum and the suppression of the leakage-inducing S mixing render the Cr7Ni molecule a suitable candidate for the qubit implementation, as further substantiated by our quantum-gate simulations.     

声子和磁场对量子环中极化子性质的影响

采用求解能量本征方程、幺正变换和变分相结合的方法,研究声子和磁场对量子环中极化子性质的影响. 对KBr量子环的数值计算表明,电子或极化子的基态能量随量子环频率(或平均半径)的增大而增大,极化子基态能移随量子环频率的增大(或平均半径的减小)而减小,极化子中的平均声子数随量子环频率的增大(或平均半径的减小)而增大. 当有垂直磁场时,极化子基态能量和基态能移与外磁场及电子转动状态有关. 随着磁场强度的增大,基态能量出现简并且呈现非周期性振荡;能移随磁场强度的增大(或转动量子数绝对值的减小)而减小.     

Structure determination, magnetic and optical properties of a new chromium(II) thioantimonate, [Cr((NH2CH2CH2)3N)]Sb4S7

The chromium(II) antimony(III) sulphide, [Cr((NH₂CH₂CH₂)₃N)]Sb₄S₇, was synthesised under solvothermal conditions from the reaction of Sb₂S₃, Cr and S dissolved in tris(2-aminoethyl)amine (tren) at 438 K. The products were characterised by single-crystal X-ray diffraction, elemental analysis, SQUID magnetometry and diffuse reflectance spectroscopy. The compound crystallises in the monoclinic space group P2₁/n with a=7.9756(7), b=10.5191(9), c=25.880(2) Å and β=90.864(5)°. Alternating SbS₃³⁻ trigonal pyramids and Sb₃S₆³⁻ semi-cubes generate Sb₄S₇²⁻ chains which are directly bonded to Cr(tren)²⁺ pendant units. The effective magnetic moment of 4.94(6)μ_B shows a negligible orbital contribution, in agreement with expectations for Cr(II):d⁴ in a ⁵A ground state. The measured band gap of 2.14(3) eV is consistent with a correlation between optical band gap and framework density that is established from analysis of a wide range of antimony sulphides.     

Application of the sublattice method to the investigation of phonon spectra and frequency density of fluorite-structure crystals

Phonon spectra and state densities of MeF₂ (Me = Ca, Sr, Cd, Ba, or Pb) crystals are calculated in the basis of sublattice state vectors using the Born–Mayer model. The phonon spectra and the sublattice state densities are calculated in the field of the second frozen sublattice. It is demonstrated that optical crystal branches are mainly due to oscillations of fluorine ions; moreover, the topology of optical branches in the spectrum and the crystal state densities are close to the topology of the spectra and state densities of the fluorine sublattice in the frozen metal sublattice. Exception is CaF₂ whose ion and cation masses are close in values.     

Thermally excited multiplet states in macerals separated from bituminous coal

Electron paramagnetic resonance searches of thermally excited multiplet states in macerals, exinite, vitrinite, and inertinite of Polish medium-rank coal (85.6 wt% C), were performed. Numerical analysis of lineshape indicates a multicomponent structure of the EPR spectra of macerals heated at 300 degrees and 650 degrees C. EPR spectra of exinite and vitrinite are a superposition of broad Gauss, broad Lorentz (Lorentz 1), and narrow Lorentz (Lorentz 3) lines. Two narrow Lorentz (Lorentz 2 and Lorentz 3) lines were observed in the resonance absorption curves of inertinite. The influence of the measuring temperature (100-300 K) on the EPR lines of the macerals was also studied. The experimentally obtained temperature dependence of the EPR line intensities were fitted by the theoretical functions characteristic for paramagnetic centers with ground doublet state (S = 12) and paramagnetic centers with thermally excited triplet (S = 1) and quadruplet (S = 32) states. Thermally excited multiplet states were found in exinite and vitrinite. Both paramagnetic centers with doublet ground state (S = 12) and paramagnetic centers with thermally excited states, probably quadruplet states (S = 32), exist in the group of paramagnetic centers of exinite and vitrinite with the broad Lorentz 1 lines. Intensities (I) of the broad Gauss and the narrow Lorentz 3 lines of exinite and vitrinite changes with temperature according to the Curie law (I = C/T). The existence of thermally excited multiplet states was not stated for inertinite. The two groups of paramagnetic centers of inertinite with Lorentz 2 and Lorentz 3 lines obey the Curie law. Copyright 2000 Academic Press.