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921.
X.Ju L.Q.Peng 《北京同步辐射装置》2001,(1):3-8
Nanowir array and film of cadmium sulfide were prepared by eletroplating in organic solvent dimethyl sulfoxide with CdCl2 and element sulfur under different temperature and current density.The UV-VIS absorption spectra show that increasing the electroplating temperature is benefit to forming perfect crystallites of energy shift for the lowest sveral excitons is given and compared with th experiment.The photoluminescence spectrum consists of two parts:the first is produced by recombination of the defcets and the second by recombination of excitons. 相似文献
922.
923.
Ming Xia LI Yan Ming WANG Ru Ru CHEN* Research Institute of Elemento-Organic Chemistry Nankai University Tianjin Pittsburgh University Medical Center Pittsburgh PA U. S. A 《中国化学快报》2001,(6)
The chiral diols ((,(,((,((-Tetraaryl-1,3-dioxolane-4,5-dimethanols) have been used for the formation of cyclic titanates and similar derivatives of Mg, Al and Zr. These complexes of oxophilic metal centers were employed in catalytic and stiochiometric enantioselective reactions such as enantioselective addition reactions of carbon-centered nucleophiles to aldehydes1, [2+2] cycloadditions2, and Diels-Alder reactions3. So far, the two hydrogen atoms of all this type of diols are in trans form… 相似文献
924.
卤素离子的质子亲和势是随卤素原子在元素周期表中的位置从上到下按F-,Cl-,Br-,I-依次降低.但人们熟知的卤素原子电负性却按F,Cl,Br,I依次减小,或者说卤素原子的电正性随上述顺序依次增大,对应于卤原子价轨道np的能量按F,Cl,Br,I依次升高;这个结果意味着卤素阴离子的电子给予能力,或者说它们的质子亲和势似乎应该随F-,Cl-,Br-,I-依次增大.这样就出现了两个完全相反的质子亲和势顺序.为了对这一结果作出解释,我们分别采用Kohn-Sham密度泛函理论(在SAOP/TZ2P和OLYP/TZ2P计算水平上),以及采用从头计算理论(在HF/TZ2P水平)中的分子轨道模型对卤素离子及卤素原子进行了详尽的理论分析.同时我们对在Hartree-Fock理论框架下轨道能量和质子亲和势的变化趋势之间存在的内在矛盾进行了阐述.研究表明质子亲和势按F-,Cl-,Br-,I-依次降低的原因是由于当卤素原子X得到一个电子成为卤素阴离子X-后,价轨道np的能量将会升高,从而表现出异常的不稳定性.更关键的是,这种由于库仑排斥造成的卤素离子价轨道的不稳定性对于本身半径比较小的氟原子尤为突出,但随着卤素的半径增大,这种不稳定效应逐渐减弱.结果较强的HOMO(F-)-LUMO(H+)轨道相互作用导致F-的质子亲和势大于其他体积较大的卤素离子.以上的定性分子轨道分析表明考虑净电荷对轨道能量的影响是十分重要的.这不仅清楚地解释了采用Kohn-Sham密度泛函理论可以得到正确的质子亲和势变化趋势,即F-Cl-Br-I-,而且还能解释为何在从头计算的Hartree-Fock分子轨道理论框架下,虽然X-的价轨道np能量随F-,Cl-,Br-,I-递减,似乎应该得到不正确的质子亲和势变化趋势,但实际上得到质子亲和势顺序仍然是正确的.之所以所有的分子轨道模型下都有同样的HOMO-LUMO相互作用能及质子亲和势顺序,其原因是电荷效应,即在HF,OLYP和SAOP计算中,卤素原子与卤素离子的价轨道能量差都是升高的.通过这些理论分析得到的结论有助于理解诸如亲核取代反应(SN2)以及碱催化的消去反应(E2)等基本有机化学反应的微观机理. 相似文献
925.
The velocity field and the associated shear stress corresponding to the longitudinal oscillatory flow of a generalized second grade fluid, between two infinite coaxial circular cylinders, are determined by means of the Laplace and Hankel transforms. Initially, the fluid and cylinders are at rest and at t = 0+ both cylinders suddenly begin to oscillate along their common axis with simple harmonic motions having angular frequencies Ω1 and Ω2. The solutions that have been obtained are presented under integral and series forms in terms of the generalized G and R functions and satisfy the governing differential equation and all imposed initial and boundary conditions. The respective solutions for the motion between the cylinders, when one of them is at rest, can be obtained from our general solutions. Furthermore, the corresponding solutions for the similar flow of ordinary second grade fluid and Newtonian fluid are also obtained as limiting cases of our general solutions. At the end, the effect of different parameters on the flow of ordinary second grade and generalized second grade fluid are investigated graphically by plotting velocity profiles. 相似文献
926.
IntroductionInrecentyears,thepharmaceuticalchemistryofpolyoxometallates(POMs)hasattract-edmuchattention[1,2].Inordertodevelopmorehighlyeffective,lowtoxicantiviralandanti-tumoralagents,attemptshavebeenmadetomodifythewell-knownKegginanions[Xn-W12O40](8… 相似文献
927.
A novel Schiff base type polyester containing 2,2’-diamino-4,4’-bithiazole(DABT) was prepared by low-temperature interface polycondensation of 1,4-benzenedicarbonyl dichloride with 4,4’-(4,4’-bithiazole-2,2’-diylbis(imine-2,1-diyl)diphenol(BDDP), which is derived from a 2,2’-diamino-4,4’-bithiazole(DABT) Schiff base reacted with a 4-hydroxybenzaldehyde monomer.The newly generated polyester was evaluated based on characterization of its solubility,FTIR spectroscopy,elemental analysis,X-ray diffraction measurements and thermogravimetric analysis(TGA) studies. 相似文献
928.
Xiubin Ren Xiangyun Guo . College of Chemistry Chemical Engineering Xi’an University of Science Technology Xi’an Shaanxi China . State Key Laboratory of Coal Conversion Institute of Coal Chemistry Chinese Academy of Sciences Taiyuan Shanxi 《天然气化学杂志》2011,20(5):503-506
Monte Carlo method was applied to simulate the oscillatory behavior during partial oxidation of methane under non-isothermal condition. The simulation was performed to examine the influences of heat transfer constant and particle size on the kinetic oscillation. The oscillatory period and amplitude were observed to increase with the increase of heat transfer constant. The increase of catalyst particle size was found to result in short oscillatory period and more or less regular oscillations combined with the formation of oxide down to L=100. 相似文献
929.
Instudyonnewpharmaceuticalsandagrochemicals,theapplicationofheterocyclesisaveryimportantmethod,whichcanimprovethebiologicalactivities.Intheseyears.moreandmorenewagrochemicalshavebeensynthesizedwhichhavethestructurescontainingheterocycles.especiallypy... 相似文献
930.
A New Capillary Electrophoresis Apparatus with Piezoelectric Ceramics High Voltage Source and Amperometric Detector 总被引:13,自引:0,他引:13
Zuan Guang CHENI Jin Yuan MO Xiao Yun YANG Li Shi WANG Xue Ting MEIZ Min Sheng ZHANGI 《中国化学快报》1999,(3)
IntroductionHighperformancecapiliar}'electrophoresis(HPCE)isanewanalyticaltechnology'rapidly'developedinrecentyears.Withtheadvantagesofsmallsample.highsensitivity,highresolution.rapidanalysisandverycheaprunning,ithasbeenappliedinchemistry'.lifescienc... 相似文献