2005 Vol. 18, No. 2

Article
The predissociation dynamics of CS2 at the g vibrational level of the 1B2(1Σu+) state has been studied, by measuring the predissociation lifetimes from the photofragment CS excitation (PHOFEX) spectrum and the rovibrational populations of CS fragment from the laserinduced fluorescence(LIF) spectrum. It is found that the angular momentum quantum number K of the g level accelerates the dissociation speed of CS2 at the 1B2(1Σu+) state, and increases the branching ratio of S(1D2)/S(3PJ) for the two dissociation channels, CS(X 1Σ+)+S(1D2) and CS(X 1Σ+)+S(3PJ). The dissociation mechanism was discussed based upon the observations.
The full potential linear augmented plane wave method is used to study the relaxation and electronic structure of (001) surface for αU. The current work predicts a contraction of the topmost layer by 2.9% accompanied by an outward expansion of the second and third layers by 1.1% and 0.2%, respectively. The relaxation of topmost and second layers makes up the largest contribution of relaxation energy. Due to the shortrange screening effect, the atomic interaction is mainly limited to adjacent layers. For the surface atoms, due to the reduced nearest neighbors, the contribution to the bonding from 5f electrons is reduced and 5f electrons appear to be more localized.
The present work is devoted to examine the passivation effect of metallic uraniu by supercritical fluid CO2, which is the most significant. The structure and thermodynamic properties of UC, C, UO2 and supercritical fluid CO2 have been calculated, based on which following simultaneous reactions have been examined using chemical equilibrium theory. The results indicate that the △G° for U(α)+CO2(g)UO2(s)+C(Graphite) reaction is -149.8~-632.0 kJ, △G° for 2U(α)+CO2(g)UO2(s)+UC(s) reaction is -725.1~-730.2 kJ, and both △G<0 and equilibrium closely approach products. It is also well known that the supercritical fluid is quite active in kinetics, and therefore the product compounds UC, C and UO2 would be quite stable. After the calculated molar tatio of UC, C and UO2, the stoichiometric ratio of elements is UC0.65±0.01O1.30±0.01, which would be useful for XPS observation.
The AM1 semiempirical calculation method was employed to study the structures and electronic properties of a series of isoxazolofullerene derivatives. Based on the AM1 geometry optimization, the electronic spectra of molecules were studied by using ZINDO/CIS methods. The results indicated the HOMOLUMO energy gaps of those isoxazolofullerenes were lower than that of C60. There existed the intramolecular electron transfer from the additional section to C60 moiety. The electronic spectrum data showed that the exception of the absorption was beyond 400 nm.The results were in good accordance with the experiment results. Nonlinear optical susceptibilities α, β and γ of molecules were calculated according to Finite Field(FF)/AM1, and the influence of molecular structures on nonlinear optical properties was examined.
A reaction mechanism of epoxidation reaction of the [4-(bromomethyl)bicyclo[4.4.1]undeca-1,3,5,7,9-pentaen-3-yl]methanol has been studied by using the density functional theory(DFT) method at B3LYP level with 631G* basis set. The geometric structures of reactant, product and transition state have been optimized. The transition state is found by the QST2 method and characterized by the vibration frequency analysis. The intrinsic reaction coordinate(IRC) for this reaction is traced and confirms the reaction mechanism. The changes and the nature of related chemical bonds along the IRC path have been analyzed by the theory of electronic charge density. The result shows that the elimination reaction and ring closing reaction are synergistic, and the hydrogen in the elimination reaction derives from hydroxyl. In addition, the activation energy of the reaction is 139.2 kJ/mol.
Dynamics of calcium oscillation in a coupled cell system is discussed. It shows that when one end of the cell chain is perturbed by noise, the signal induced by noise can propagate along a linearly coupled cell chain with considerable enhancement, a rather ordered internal signal can be obtained on the other end, and the signal itself can also be enhanced. The effects of coupling constant, noise intensity and coupling means on the propagation of the signal are investigated. It is found that there exist an optimal coupling constant and noise intensity in favor of the signal propagation. What′s more, a qualitative explanation via the signal and the noise background is given. And the oneway coupling is better for the signal propagation and enhancement than for the twoway coupling. The results may have important applications in living cell systems, where information is transmitted along a cell chain.
In order to study the changing process of Barium strontium titanate (BaxSr1-xTiO3, BST) from cubic phase to the tetragonal phase with Ba doping and the ferroelectric characteristic of BST, the total energy of BST with different mole ratio of Ba/Sr when Ba doped was calculated and the fine structure determined, based on general gradient approximation, by means of ultrasoft pseudopotentials plane wave method. It is demonstrated that in BST, the cell volume expands and the value of c to a increases when Ba doped, which cartributed to the separation of positive and negative ions and selfpolarization. The tetragonal Ba0.8Sr0.2TiO3 behaved as ferroelectric when the offcenter displacement of Ti was up to 8 pm along \[001\] direction.
The theoretical and experimental validation was made to Lorenz function model of refractiveindex distribution in gradedindex polymer optical fiber (GI POF) by experimental data. It was found that simulating error is great when molecule bulk ratio is larger than one. According to calculating results, exponent parameter of the molecule bulk ratio in the model was corrected to 1.1, so the simulating error was remarkably reduced from ≤65% to <20%. It showed that influence of the molecule bulk ratio on refractiveindex distribution in GI POF is great.
The molecular dynamics method was adopted to investigate the tension deformation for SWCNTs with different chiralities and radius. The results show that nanotubes have an extremely large breaking strain. Carbon nanotubes are completely ductile before their structural defects appear. Through tracing the evolution of the spacial configuration of a microstructural cell of SWCNTs, it is found that the torsion deformation results in the change of structural symmetry. Thus the load is no longer welldistributed. The structural defects will occur with further loading. The systematic energy change of SWCNTs is observed. It can be seen that there is a structural transformation around the initial vacancy defects when the axial tension strain reaches a certain value. The two adjacent hexagons change to one pentagon and one heptagon (also called the StoneWales transformation). The 57 configuration makes strain energy release, and the systematic energy falls. This configuration is more preferable from the viewpoint of the energy. The results also show that fewer defects have weak influence on the mechanical properties of SWCNTs under the present initial vacancy defect condition.
The molecular dynamics method has been applied to simulate the melting temperatures of CaF 2 at elevated temperature and high pressure and to calculate the P~V equation of state of CaF 2 up to 100 GPa at 300 K. The interatomic potential was taken to be the sum of pairwise additive Coulomb, van der Waals attractions, and repulsive interactions. In addition, the shell model was used in molecular dynamics simulation. The pressure dependence of the melting temperature of CaF 2 was predicted up to 4 GPa. However, in order to account for the superheating melting of the molecular dynamic simulation, the simulated melting temperatures of CaF 2 were corrected by the modern theory of melting. Consequently, the melting temperatures of CaF 2 were accurately obtained at elevated temperature and high pressure. Therefore, it is shown that shellmodel molecular dynamics simulation at constant pressure indeed provides a useful tool for studying the melting temperatures of other materials under high pressures.
At first a comprehensive and short review on the characteristics for size growth-rate of crystals is presented. Based on the structural model of micro-nucleus- and crystal-constituent chains and the feature of grown mechanism for crystallization by the molecular segregation of stems, a general principle and method for characteristics of the number growth-rate for micro-crystal-constituent chains and the size growth-rate for crystals by melt-crystallization was proposed. According to the principle, a set of quantitative expressions for the number growth-rate of constituent chains with different sizes and different lengths of segments and the size growth-rate of crystals by four different types of growth with folding, extending, parallel combination of folding and extending and series combination of folding and extending chains was derived by the combination method of statistical mechanics and kinetics. Then four growth-rate equations for the number of constituent chains and the size of crystals produced by four different types of growth are also obtained. These equations can be successful in relating the growth-rate-to the different types of growth and temperature of crystallization and supper-cooling.
A new structure information autocorrelation topological index tX is designed and developed based on the vertex degree of molecular topology and autocorrelation function of mathematics. Quantitative structureproperty the relationships for estimating the refractive index of cycloalkane and alkane are set up based on multiple linear regression. The vertex degree is defined as βi .The structure information autocorrelation topological index tX is set up with the βi. The refractive index (nD), for the 64 cycloalkanes, are correlated with this topological indices. The index, for the 27 alkanes, are also correlated with this topological indices. The calculated results showed that the calculated refractive index of cycloalkanes and alkanes are in good agreement with the experimental data, with the mean velative deviation 0.25%. With the established model, the refractive index of the other 5 alkanes are predicted.
The bismuth glasses with Er3+ and Er3+/Yb3+ codoped were fabricated by the technique of hightemperature melting. The absorption and fluorescence spectra, fluorescence lifetime and FWHM were measured. The explanation of concentration quenching in case of high level Er3+doped the bismuth glasses is given. The sensitizing of Yb3+ to Er3+ in Er3+/Yb3+ codoped bismuth glasses is discussed. The explanation of the influence on absorption and fluorescence spectra, fluorescence lifetime and FWHM in case of the change of Er3+ or Yb3+ in bismuth glasses with Er3+/Yb3+ codoped is given. It is found that the change of Er3+ content has obviously influenced the fluorescence lifetime and FWHM while the change of Yb3+ content has remarkably influenced the absorption and fluorescence intensity. The band at around 1.54 μm in Er3+/Yb3+ codoped bismuth glass reaches 76 nm and the fluorescence lifetime is 0.55 ms.
Order character and lamellar structure of TritonX100/nC10H21OH/H2O lamellar liquid crystal were investigated. Partial phase diagram of TritonX100/C10H21OH/H2O was measured at 25℃ by the polarizing microscope, and lamellar structure of the lamellar liquid crystal was verified by the 2H NMR spectra. The ESR spin probe method was used to detect the changes in the lamellar liquid crystal. A stearic acid, 5doxylstearic acid, was used as the spin probe. The values of hyperfine coupling constant and order parameter of lamellar liquid crystal in the phase diagram were calculated. The values of the hyperfine coupling constant with different composition were almost unchanged. It indicates that the micropolarity of the lamellar liquid crystal is very similar. The order parameter decreases with the increasing water content in lamellar liquid crystal. It can be explained by considering that: First, though the penetration is determined at the given weight ratio of C10H21OH to TritonX100, the absolute water content penetrated into the amphiphile bilayer increases with the increasing of the water content. Second, the thickness of the solvent also increases, which makes the force between layers weaker. The results also showed that order parameter of lamellar liquid crystal increased with TritonX100 content, which may be explained from the fact that the water content penetrated into the amphiphile bilayer decreases relatively and the molecules in the amphiphile bilayer are made tighten. The interlayer spacing of lamellar liquid crystal was determined by small angle Xray diffraction. The penetration ratio of water in the lamellar liquid crystal was calculated. It was about 50%.
The pore structure of extending PTFE(ePTFE) membrane by the stretching method is much different from other polymers. The image analysis of Scanning Electron Microscope(SEM) was used to describe the fiberized PTFE molecular and the coagulated PTFE node. The interconnected notes and fibrils were defined as numerical parameters, LF, WF, LN, WN and AN. The results by description of the SEM image analysis were corresponding with the porosity Pr and density Pf in the combination method of bubblepressure and fluid permeability used in other microporous membranes. The membrane with bigger AN images of node gave larger Pf and smaller Pr, and membrane with smaller AN images showed smaller Pf and bigger Pr. However there was no certain relationship with r or rmax. It is said that the SEM image analysis can be used as one of the methods to describe the pore performance of ePTFE membrane. Moreover, the influences of molecular weight of PTFE, and the stretching ratio at mechanical operation on ePTFE pore structure could also be interpreted by the SEM image analysis. The bigger molecular weight of raw material PTFE, the higher porosity and strength of the membrane would be found. The less stretching ratio, the bigger crystal node and the shorter fibril SEM image were observed.
A series of Sc3+-doped spinel lithium manganese oxides Li1+xScyMn2-yO4(y=0.01, 0.02, 0.06, and 0.10)were synthesized by solid state reaction using LiOH·H2O, MnO2, and Sc2O3 as starting materials. The results of powder X-ray diffraction indicated that the doped Li1+xScyMn2-yO4 maintain the cubic structure of spinel phase Fd3m. The electrochemical properties were characterized by electrochemical methods. The initial discharge capacity reached 135 mAh/g and the capacity fading rate was less than 2% after 40 cycles. The spinel phase was well preserved after 40 cycles. The doping of Sc3+ effectively improved the cycleability of spinels, and was a promising way for the improvement of spinel LiMn2O4 cathode materials.
SnO nanowhiskers were successfully prepared by the pressurethermalcrystallization method using SnCl2·2H2O as raw material, Na2CO3 as mineralizing reagent and cetyltrimethylammoniumbromide as surfactant. Microstructure and morphology of the prepared products has been characterized by means of transmission electron microscopy,selected area electron diffraction and X-ray diffraction. The results showed the particle has rodlike apparent structure. The diameter and the length of the particle were 10~40 nm and 100~400 nm, respectively. The influence of some reaction parameters, including the pressure, the surfactant and the reaction duration, on the formation, morphology and particle size of SnO crystallite was discussed. It revealed that increasing the pressure and prolonging the reaction time duration are favorable for the formation of tetragonal stannous oxide whiskers. The mechanism of the formation of SnO nanowhiskers was also simply investigated.
Dense oxygen permeable membranes are expected to have great impact on oxygen production and oxygeninvolved industrial processes. Ba0.5Sr0.5Co0.8Fe0.2O3-δ is of highest oxygen permeability at elevated temperatures. A novel composite ceramic preparation route for Ba0.5Sr0.5Co0.8Fe0.2O3-δ was developed by directly produced stable BaZrO3based secondary phase particles(SPP) via addition of ZrO2 and isomolar excess BaO, aiming at improving mechanical properties. It revealed that assynthesized composites could get a welldeveloped and finegrained microstructure, there being secondary phase particles as the grain growth inhibitor, and the mechanical properties and oxygen permeation are improved. For the composite with addition of 10% ZrO2+10% BaO, a welldeveloped and finegrained microstructure has been obtained. Compared to the pure phase BSCF5582, the threepoint bending strength of the composite with addition of 5% ZrO2+5% BaO increases by 68% and its oxygen permeation rate is much higher below 850℃ with the smaller apparent activation energy. Additionally, the electrical properties of the composites are also affected by the inclusion of SPP: conductivity decreases with the SPP content increasing, while the hysteresis of conductivity declines due to the relative stable carrier concentration.
The light-to-electricity conversion process of the TiO2 nanostructured electrode sensitized by a dye was investigated using the photoelectrochemical method in this paper. At the same time, the WO3 thin film was electrodeposited on conducting glass. The results showed that the dye-sensitized nanoporous TiO2 film has the properties of energy conversion, along with good electrochromic properties of electrodeposited MoO3 thin film. A self-powered smart window was achieved by combining a dye-sensitized nanoporous TiO2 film as the photovoltaic layer and an electrodeposited WO3 film as the electrochromic layer. This window changed from being almost transparent to blue spontaneously under illumination, and thus could modulate light transmittance.
The coprecipitation method was used to prepare a series of different oxides (CuO: 0, 5%, 10%, 15%, 20%, 30% and 40%) derived from Cu substituted Mg/Almixed anionic clay precursors (hydrotalcites) at the ratio of M2+/M3+ =3. In order to study influences of Cu and Mg content upon the performance of these materials, such characterization techniques as X-ray diffraction, thermogravimetrical analysis, differential scanning calorimetry, temperature programmed reaction and Fourier transform infrared reflectance spectra, were used. The results showed that complete structure of hydrotalcite precursors could be formed when CuO≤30%. When CuO≥40%, Cu(OH)2 phase appeared. Homogeneous composite oxides can be obtained by high temperature calcination at CuO≤20%. When CuO>20%, CuO phase was isolated. The content of Cu and Mg had significant influences on thermal stability of materials. The reduction ability of materials was related to calcination temperatures and material composition.
TAI (4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene) significantly influences ultra-fine AgBr/I particle growth in aqueous fish gelatin. IR spectrum shows that the NH stretching vibration band of TAI is absent in ultra-fine AgBr/I particle/fish gelatin emulsion, indicating the formation of N-Ag bond and the adsorption to AgBr/I particles. By the analysis of UV adsorption spectrum, it is shown that the amount and percentage coverage of TAI adsorbed to ultra-fine AgBr/I particle is related with the physical ripening process of emulsion. With ripening for 5min, the amount of TAI adsorbed per unit area of AgBr/I particle and percentage coverage of TAI on the particle surface reached maximum, which may be attributed to a suitable space structure of TAI-Ag compounds. As the ripening time was prolonged, the adsorption amount per unit area and percentage coverage of TAI adsorbed on the surface of ultrafine AgBr/I particle showed a tendency to level off on the whole, i.e. 1.3 μmol/m2 and 47%~49%, respectively. By TEM observation, the largest average diameter of ultra-fine AgBr/I particles appeared after physical ripening for 5 min. No significant change of the average diameter and size distribution of the particles was observed when the ripening time was prolonged continuously. In the case of TAI addition, the average diameter and growth rate of ultra-fine AgBr/I particles in aqueous fish gelatin solution was obviously smaller than that without TAI addition, indicating TAI protection for ultra-fine AgBr/I particles in emulsion. Under cooperative action of TAI and fish gelatin, the average diameter and size distribution of ultra-fine AgBr/I particles hold relative stability.
The AlPO4-5 molecular sieve has been synthesized hydrothermally by using tripropylamine (TPA) as the template, and pseudoboehmite and orthophosphoric acid as aluminum and phosphorus sources, respectively. The single crystals of AlPO4-5 with different sizes have been obtained by varying the molar ratio of reactants and the crystallization conditions (such as the temperature and time). The typical molar ratio of the reactive mixture is Al2O3∶P2O5∶TPA∶C2H5OH∶H2O∶HF=1∶1.2∶2.66∶80∶1000∶0.7, and perfect AlPO4-5 large single crystals with the maximum length up to 2.0 and 0.31 mm transverse dimension have been prepared by crystallizing the mixture at 457 K for 48 h. Scanning Electron Microscopy (SEM) has been employed to observe the sizes and morphologies of the large single crystals of AlPO4-5. The structure of AlPO4-5 single crystal has been refined by the SMART 1000 single crystal diffractometer.
CNx nanotubes have been synthesized by thermal decomposition of ferrocene/ethylenediamine (Fe(C5H5)2/C2H8N2) mixture using ferrocene as the catalyst at 800~1040℃. Transmission electron microscopy (TEM) and Raman spectroscopic were used to characterize the CNx nantoubes produced at different temperatures, whose yields were also investigated. It is shown that the CNx nanotubes have bamboolike structure, and the average diameter, crystallinity and yields increase with the temperature increasing. X-ray photoelectron spectrum (XPS) revealed the nitrogen incorporation of the CNx nanotubes. The catalysis mechanism of ferrocene in the growth of the CNx nanotubes is also discussed.
The metallic Cu modified n-p coupled semiconductor Cu/ZnO-TiO2 was prepared by the solgel method, and its surface structure, absorptivity of ultraviolet light, chemisorption properties and photocatalytic behaviors were investigated by techniques of X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), BET surface area (BET), Infrared absorption spectra (IR), UV-visible diffused reflectance spectra (UV-vis) and photo stimulated surface catalytic reaction. The results show that the main crystal structure of the catalyst is anatase TiO2 with the particle size about 10 nm. The Zn-O-Ti bond is formed and the absorption intensity in the wavelength region of 250~400 nm is enhanced through the coupling of ZnO and TiO2, while the absorption region is expanded to visible light with the UV absorbance limit shifting to the shorter wavelength region after Cu supported on the coupled semiconductor ZnO-TiO2. The adsorption states of reactants are important factors influencing the results of photocatalytic reaction, while the bridge adsorption state of CO2 formed on Cu and Lewis acid sites Ti4+ and undissociated of C2H4 formed on Cu and Lewis base sites bridge-O are the effective intermediates to synthesize the crylic acid with the selectivity over 87% under the temperature of 100℃.
Cu-Cr and Cu-Cr-Zr catalysts for the low temperature methanol synthesis slurry phase, with the surface area of 77.9 and 113.2 m2/g respectively, were prepared by the coprecipitation approach. The activity and selectivity of these catalysts were evaluated in a stainless steel autoclave at 5.5 MPa and at different temperatures of 383 and 423 K separately. It was found that the activity of Cu-Cr-Zr catalyst was obviously higher than that of Cu-Cr catalyst, whereas the methanol selectivity of Cu-Cr-Zr catalyst was a little lower. The concentration of sodium compounds in the solution after reaction was also measured. The results showed that the concentration of sodium formate after reaction is much lower than that before reaction, which is quite different from the observations from the Cu-Cr catalyst previously. This implies that the conversion of sodium methoxide to sodium formate has been completely suppressed in the presence of zirconia in Cu-Cr-Zr catalyst. This finding is more beneficial to improve the performance of Cu-Cr catalyst and to increase the life of catalyst system as well.
The rare-earth perchlorate complex compound with DL-α-Glycin was synthesized. Its structure was characterized as [Pr2(DL-α-Gly)6(H2O)4](ClO4)6·5H2O by TG, DTA and chemical analysis, and the purity was 99.63 %. The melting point analysis experiment indicates that the complex has no stable melting point. The heat capacity of the complex was measured by a high-precise fully-automated adiabatic calorimeter from 79 to 371 K. No obvious abnormal heat capacity was observed within this low temperature range. The thermal decomposition temperature range of the complex was near 333 K. Its decomposition temperature, decomposition enthalpy and entropy were 320.010 K, 40.714 kJ/mol and 127.227 J/molK, respectively. The polynomial equation of heat capacity of this compound was simulated by the computer within the temperature range of 78.939~301.295 K. The standard enthalpy of formation was -8022.802 kJ/mol measured by isoperable reaction calorimeter at 298.15 K.