Nd_(1-x)Ba_xMnO_3和La_(0.67)Mg_(0.33)Mn_(0.85)M_(0.15)O_3(M=Mn,Ga,Fe)中Mn位自旋磁矩对电导性的影响

研究了Ｎｄ１－ｘＢａｘＭｎＯ３和Ｌａ０．６７Ｍｇ０．３３Ｍｎ０．８５Ｍ０．１５Ｏ３（Ｍ＝Ｍｎ，Ｇａ，Ｆｅ）的导电性，发现Ｍｎ位的自旋磁矩排列状态和大小对体系的导电性有强烈的影响．在Ｎｄ１－ｘＢａｘＭｎＯ３中，当Ｍｎ３＋／Ｍｎ４＋的浓度比值为２∶１，１∶１，１∶２时，电阻率出现半导体－金属转变．推论该类体系的导电性首先由体系中Ｍｎ３＋和Ｍｎ４＋自旋磁矩形成的磁结构状态决定，然后才取决于由Ｂａ掺杂浓度所决定的载流子浓度．在Ｌａ０．６７Ｍｇ０．３３Ｍｎ０．８５Ｍ０．１５Ｏ３（Ｍ＝Ｍｎ，Ｇａ，Ｆｅ）中，Ｍｎ位自旋磁矩大小的改变对导电性有强烈的影响，另外发现该类体系均以变程跳跃模式进行导电．     

La2O3—BaO系复氧化物的现场拉曼光谱研究

对于Ｌａ０．２Ｂａ０．８－ｘＣａｘ（Ｏ，ＣＯ３）其中ｘ＝０．０、０．２、０．４、０．６氧化物在９７３Ｋ及甲烷氧化偶联（ＯＣＭ）条件下，无Ｃａ＾２＋的样品可用表面ＢａＣＯ３和（ＬａＯ）２ＣＯ３的Ｒａｍａｎ谱及８１０ｃｍ＾－１附近的Ｏ２＾２－特征峰来表征；含Ｃａ＾２＋的样品，则表现了混合碳酸盐（Ｃａ，Ｂａ）ＣＯ３的特征，还有位于１１３５ｃｍ＾－１（ｗ）和８１０ｃｍ＾－１（ｗ）的Ｏ２＾－、Ｏ２＾２－瞬时     

粲夸克偶素P波态χ_（c0）宽度测量

利用北京谱仪在北京正负电子对撞机上采集的３５０万（２Ｓ）事例，通过（２Ｓ）→γπ－和γＫ＋Ｋ－反应道测量了Ｘｃ０的总宽度．由ＭｏｎｔｅＣａｒｌｏ模拟给出的质量分辨函数，利用拟合Ｘｃ２谱形得到的质量分辨作标定后，用于Ｘｃ０宽度的拟合，得到Ｘｃ０的宽度为（１５．０）ＭｅＶ．同时定出了ＸｃＪ（Ｊ＝０，２）到π＋π＝和Ｋ＋Ｋ－的衰变分支比．结果为Ｂ（Ｘｃ０→π＋π－）＝（４．２７±０．２３±Ｏ．６０）×１０－３；Ｂ（Ｘｃ０→Ｋ＋Ｋ－）＝（３．４４±０．２１±０．４７×１０－３；Ｂ（Ｘｃ２→π＋π－）＝（１．５２±０．１７±０．２９）×１０－３和Ｂ（Ｘｃ２→Ｋ＋Ｋ－）＝（５．２±１．１±１．８）×１０－４，其中第一项误差为统计误差，第二项为系统误差。     

（La2／3Ca1／3）（Mn（3—x）／3Gax／3）O3体系巨磁电阻效应和电特性的研究

采用固态反应法制备了（Ｌａ２／３Ｃａ１／３）（Ｍｎ（３－ｘ）／３Ｇａｘ／３）Ｏ３（ｘ＝０．００，０．１０，０．１５，０．２０，０．３０）体系的系列样品。通过系统地测量其零场和１．６特斯拉（Ｔ）磁场下样品的电阻率－温度关系以及一定温度下磁电阻率与磁场的关系，发现随Ｇａ＾３＋替代量的增加其磁电阻率峰和电阻率峰均向低温方向移动，磁电阻率峰值增大，并伴生磁电阻率峰展宽效应。作者认为，上述结果是由于Ｇａ＾３     

吡啶B_1(nπ~* )态(2 3)偏振共振多光子电离谱中6a_0~1带型模拟及转动常量确定

通过模拟吡啶Ｂ１（ｎπ）态（２＋３）偏振共振多光子电离谱中转动结构可部分分辨的６ａ１０带型,获得了该态上吡啶分子的转动常量,分别为Ａ′＝０２１６７０ｃｍ－１,Ｂ′＝０１６７５８ｃｍ－１,Ｃ′＝００９４５０ｃｍ－１．表明氮原子上的一个孤对电子跃迁进入π轨道后氮原子自身电负性减弱,吡啶分子构架总体上张开．此外,比较６ａ１０实测谱带与理论曲线,发现了湮没于６ａ１０谱带高强度之下尚未见报道的１７ａ１０６ａ１０１２１０和１１ｂ１０两个谱带     

La_（2－x）Sr_xCu_（1－y）Fe_yO_4正常态的反常磁性

研究了Ｌａ２－ｘＳｒｘＣｕ１－ｙＦｅｙＯ４（ｘ＝０．１３，０．１５，０．１７和ｙ＝０．０，０．００２，０．００４，０．００６）多晶样品在不同磁场下（Ｈ＝１，３和５Ｔ）正常态直流磁化率与温度的关系和超导转变温度与Ｆｅ掺杂含量的关系．结果表明，不掺杂样品的正常态直流磁化率呈宽峰行为．随着Ｆｅ掺杂量的增多，直流磁化率与温度的关系由宽峰行为变为Ｃｕｒｉｅ－Ｗｅｉｓｓ行为．与此同时，超导转变温度随Ｆｅ掺杂含量的变化而变化．这表明载流子浓度是影响超导的重要因素．对Ｆｅ掺杂样品，其正常态直流磁化率与温度的关系可以用Ｘ＝ａ＋ｂＴ＋ｃ／（Ｔ－Ｔ０）很好的表示．我们认为，其中ａ＋ｂＴ项是带Ｐａｕｌｉ顺磁的贡献．对同一掺Ｆｅ样品，增加外磁场时，居里常数ｃ增大而常数项ａ减小．这是由于在Ｆｅｒｍｉ面存在不满的窄带（ｄｘ２上Ｈｕｂｂａｒｄ带），它是导致居里顺磁的原因．增加磁场时它往高能方向移动，窄带的电子空得更多，这些电子移向较宽的杂化带，导致每个Ｃｕ离子的磁矩增大，而带的Ｆｅｒｍｉ面电子态度减小．我们的实验结果也表明，超导电性与能带结构密切相关．     

Gd＿（1－x）Ca＿xBa＿2Cu＿3O＿（7－y）高温超导体压力效应的研究

研究了Ｇｄ＿（１－ｘ）Ｃａ＿ｘＢａ＿２Ｃｕ＿３Ｏ＿（７－ｙ）（０．０≤Ｘ≤０．２０）高温超导体在常压和高压下的超导电性在１－３００Ｋ温度范围内，利用Ｂｒｉｄｇｍａｎ对顶砧获得压力达９．０ＧＰａ，测量了（Ｘ＝０．１０，０．１５，０．２０）样品的ｄＴ＿ｃ／ｄｐ分别为７．６８，７．８和４．４６Ｋ／ＧＰａ。发现Ｔ＿ｃ的压力导数随着ｃａ￣（２＋）含量的增加而下降，分析了氧含量对Ｔ＿ｃ和ｄＴ＿ｃ／ｄＰ的影响．利用常压下晶格参数精修值和阳离子与氧离子间距随压力的改变，说明ＣｕＯ＿２面在超导电性上的作用，用ＣｕＯ＿２面之间耦合解释Ｔ＿ｃ（Ｐ）曲线的非线性关系。     

Bi2Sr2Ca(Cu1-xMnx)2Oy单晶的结构与超导电性

用自助熔剂法制备了Ｂｉ２Ｓｒ２Ｃａ（Ｃｕ１－ｘＭｎｘ）２Ｏｙ（ｘ＝０．０１,０．０５,０．０８,０．１０）单晶。单晶的ｃ轴长度随Ｍｎ含量的增加而减小。Ｒ－Ｔ曲线测量表明,零电阻温度Ｔｃ随ｘ的增大面逐渐下降。对Ｍｎ掺杂量较高的一些单晶,发现其Ｒ－Ｔ曲线在１０５Ｋ左右有一陡降,表明Ｍｎ掺杂量较高的单晶中可能有微量的Ｂｉ２２２３相成分存在。     

棱镜产生最小偏向角的充要条件

光学教程分析了棱镜产生最小偏向角的必要条件,但其讨论过程不易被初学者所理解,且没有涉及产生最小偏向角的充分条件．本文将对其做适当改进,使之更简明、更完善． 如图１所示,ＳＢ为入射光线,经棱镜折射后成为ＣＳ′,两光线夹角θ称为偏向角．由图１知： 按折射定律有： ｉ１＝ａｒｃ ｓｉｎ（ｎｓｉｎ ｉ１）, ｉ′１＝ａｒｃ ｓｉｎ［ ｎｓｉｎ（ａ－ ｉ２）］,θ＝ａｒｃ　ｓｉｎ（ｎｓｉｎ　ｉ２）＋ａｒｃ　ｓｉｎ［ｎｓｉｎ（ａ－ｉ２）］－ａ（２）（２）式表明,θ随ｉ１的改变而改变,而偏向角有一最小值的必要条件是： …     

对Bi-2212超导体中的Raman谱指认

本文对Ｂｉ２－ｘＰｂｘＳｒ２ＣａＣｕ２Ｑδ（ｘ＝０￣０．５）系列样吕以及在真空下不同温度退火的Ｂｉ１．６Ｐｂ０．４Ｓｒ２ＣａＣＵ２Ｏδ样品进行了Ｘ射线衍射和Ｒａｍａｎ谱实验研究。测量表明,随着退火温度的升高,ａ,ｂ,ｃ轴晶格常数增加,与Ｏ（１）ＣｕＢｇ模式相关的２９４ｃｍ＾－１的峰强减少,峰位红移。研究结果进一步表明,４６４ｃｍ＾－１和６３０ｃｍ＾－１峰分别与Ｏ（３）ＢｉＡ１ｇ和Ｏ（２）ＳｒＡ１ｇ     

The excitonic and zero-field splittings of the first triplet state of toluquinone single crystals

The pure electronic S ₀ → T ₁ transition of toluquinone has been studied in absorption using single crystals at 6 K and polarized light. The theory of the Zeeman effect on the crystal exciton levels is developed and compared with the experimental results. High-field measurements show that the factor group splitting is 0·32 cm^-1 and that the orbital plus state lies at higher energy. The ordering and energy separation of the magnetic substates of the factor group levels is also obtained. The latter results are confirmed by low field measurements and the following molecular zero-field splitting parameters are obtained: Y = +0·12, X = -0·02 and Z = -0·09 cm^-1.     

Thermodynamic perturbation theory for the (12-6-n) fluids

A perturbation method in which attractive forces are taken as perturbation of the repulsive (reference) forces is applied to calculate the thermodynamic properties of (12-6-n) fluids in terms of the properties of hard-sphere fluid. The numerical values of the thermodynamic properties (free energy per particle, compressibility and excess internal energy) for a range of temperature and density are given for (12-6-8) fluids. Further, two perturbation schemes are adopted to evaluate the total radial distribution function using the EXP version of the optimized cluster theory (OCT). The numerical results are reliable as reported at two states (T* = 1·036,ρ* = 0·65 andT* = 0·719ρ* = 0·85) for the (12-6-8) fluid and the Lennard-Jones (12-6) fluid as well.     

Thermal conductivity of nitrogen in the temperature range 350–2500 K

The thermal conductivity of nitrogen is determined in a conductivity column instrument in the temperature range of 338 to 2518 K with an estimated uncertainty of about ± 1·5 per cent. The experimental data points are correlated by a cubic polynomial in temperature, viz. k(T)/(mW m^-1 K^-1) = 12·18 + 0·05224(T/K) - 0·6482 × 10^-6(T/K)² - 0·2765 × 10^-9(T/K)³. These conductivity values determined from heat transfer data taken in the continuum regime are found to be in fair agreement with the values obtained from similar data referring to low pressure range.

The present results are compared with the conductivity determinations of other workers and with the predictions of various theories developed for polyatomic gases. It is pointed out that a reliable calculation of thermal conductivity over an extended temperature range is impossible at the present time due to the absence of a large variety of experimental molecular data needed for such an effort. Average values of the vibrational energy diffusion coefficient, D _vib, are computed from the present k(T) data.     

Methyl group tunnelling and torsion in 2,4-hexadiyne

The tunnelling splitting of the ground torsional level of solid 2,4-hexadiyne and transitions to excited torsional states have been measured at low temperatures using neutron inelastic scattering. At 4 K the tunnelling splitting is 1·060 μeV (0·0086 cm^-1). It decreases as the temperature is raised, to 0·834 μeV (0·0067 cm^-1) at 35 K, and to less than 0·6 μeV at 50 K. A V-2←V=0 transition in the torsional vibration has been observed at 222 cm^-1 which shifts to 160 cm^-1 in the fully deuterated compound.

The values of the torsional frequencies, tunnelling frequency, and the change of tunnelling splitting with temperature have been fitted exactly to a potential energy for rotation of a methyl group given by

with a barrier to rotation of 432 cm^-1.

Changes in the tunnelling transitions as the temperature increases are compared with existing theories of the mechanism.     

Substituent effects in cooperativity of chalcogen bonds

In the present work, substituent effects on cooperativity of S···N chalcogen bonds are studied in XHS···NCHS···4-Z–Py (X = F, Cl; Z = H, F, OH, CH₃, NH₂, NO₂, and CN; and Py = pyridine) complexes using ab initio calculations. An increased attraction or a positive cooperativity is observed on introduction of a third molecule to the XHS···NCHS and NCHS···4-Z–Py binary systems. The shortening of each chalcogen bond distance in the ternary systems is dependent on the substituent Z and is increased in the order Z = NH₂ > OH > CH₃ > H > F > CN > NO₂. The electronic aspects of the complexes are analysed using molecular electrostatic potential, and the parameters derived from the atoms in molecules and natural bond orbital methodologies. According to interaction energy decomposition analysis, the electrostatic energies are important in the interaction energy of S···N bonds and may be regarded as being responsible for the stability of these complexes.     

On the real part of the amplitude of elastic scattering of proton on deuteron at an energy of 8 GeV

The elastic scattering of a proton on a deuteron at an energy of 8 GeV is studied by the method of multiple transitions of protons through a target 1·5 μ thick, made from (CD ₂)_n. Altogether 27,385 reflected deuterons were recorded and measured by means of nuclear emulsions. From an analysis of the course of the differential cross-section as a function of the scattering angle in the limits of 1·4° to 8·9° (¦t¦= 0·0042 – 0·1750 (GeV/c)²) we determined the ratio of the real and imaginary parts of the scattering amplitude

$$\alpha = \frac{{\operatorname{Re} A(0)}}{{\operatorname{Im} A(0)}} = - 0 \cdot 36 \pm 0 \cdot 08$$     

Simulation of molecular orientational dynamics in a model polar fluid

A molecular dynamics simulation of a Stockmayer fluid with μ* = 1·0, ρ* = 0·7 and T* = 1·13 (±0·03) is reported. In addition to evaluations of a number of static properties, orientational time correlation functions C_l (t) = <P(cos δθ(t))> were calculated for l = 1 through 4 ; P_l is a Legendre polynomial and δθ(t) is the angle of reorientation of the dipole in time t. These time correlation functions are characteristic of nearly free rotation and agree well with curves calculated from a perturbation theory for the memory functions that utilizes the simulated value of the mean square torque. The angular velocity autocorrelation function for this fluid was also simulated and compared with perturbation theory. Agreement is not good, primarily because of the presence of a pronounced long time tail in the simulated function. The relationship between these results and those of other simulations and theories is discussed.     

1H NMR study of lithium D-lactate.

Polycrystalline D-lactic acid lithium salt [(R)-2-hydroxypropanoic acid lithium salt, lithium D-lactate] has been investigated by pulsed proton magnetic resonance methods between 77 and 300 K at 25 MHz. The main relaxation mechanism is methyl rotation; the motion is characterized by an activation energy Ea = 14.5 +/- 0.5 kJ/mol and time factor tau 0 = (1.5 +/- 0.5) x 10(-13) s. The activation energy is higher than the potential barrier obtained by ESR and ENDOR techniques for methyl rotation in the lactate radical. The methyl rotation is also responsible for a reduction of the dipolar second moment. Below 100 K the reduction of the dipolar second moment is ascribed to quantum-mechanical tunneling; an excitation energy of 6.1 +/- 1 kJ/mol is derived from a contribution to the spin-lattice relaxation times from the tunneling.