2001 Vol. 14, No. 3

Article
CCl2free radicals were produced by dc discharge of CCl4(in Ar). Ground electronic state CCl2radical was electronically excited to A1B1(0,4,0) state with Nd:YAG laser pumpeddye laser at 541.52nm. Experimental quenching data of CCl2(A1B1and a3B1) by several ketones were obtained through observing time resolved fluorescence signal of the excited CCl2radicals, which showed a superposition of two exponential decay components. The state-resolved rate constantsKAandKawere first time acquired by analyzing and dealing with these data by using three-level-model, which was put forward by us.KAandKaincrease on the whole with increasing the number of C-H bonds in ketones.
The square-well potential function is considered as the superposition of hard sphere potential and a short range uniform negative potential. From this,the corresponding equation of state which contains two localized radial distribution functions is derived by statistical mechanics. The molecular dynamic data of compressibility factor are used to regress this two localized radial distribution functions. Therefore, a new equation of state of square well fluids is established. Its attractive term is much simpler than that proposed by Alder et al. and the consistency with MD data for compressibility factor is also better at the area of higher densities.
This paper introduces a new control scheme for controlling stochastic multiresonance (SMR) in two kinds of systems, through the variation of the noise pulse interval or intensity by computer simulation. Meanwhile, in quantum dissipative two-level system, quantum stochastic multiresonance can be realized by adjusting the quantum noise. In addition, this paper explained how the SMR forms in this kind of system by using the concept of hopping between different energy levels. The aspects of the SMR in this system are discussed.
Ab initioand density functional theory calculations have been carried out on the trinitrogen clusters: N3, N3-and N3+using seven different theoretical methods at 6-311+G* basis set level. The calculated results of the known structures agree well with the experimental values. The stable geometry structures of the experimentally unknown species and their relevant properties have also been obtained. The effect of the calculational methods to the various calculated results (geometrical parameters and the harmonic frequencies and relative stability) of three trinitrogen clusters are compared. The bonding character has been analyzed using the bonding energies and molecular orbital theory.
Structure and energetics of silver clusters, AgN(N=3141), have been studied bmolecular-dynamics simulation. A model many-body dual potential function has been used in our simulations. Stable structures of microclusters with sizesN=313 and the energetics of clusters generated from FCC crystal structure with sizesN=13141 have been determined by molecular-dynamics simulation. It has been found that three dimemsinal structure of spherical cluster appears forN=13 141. The caculation of average binding energy of silver clusters has been performed and the relationship plot between the binding energy and the cluster sizes also has been given. As the cluster size increases the calculated binding energy approachs the bulk cohesive energy.
Using the B3LYP method with the relativistic effective core potential and contract valence electron basis set [5s4p3d4f]/[3s3p2d2f] for U and Pu atom, the present work optimized the structure of U2and Pu2dimers. Their long-bond-length and short-bond-length are found, which are 0.38965 nm, 0.29927 nm for U2and 0.45375 nm, 0.35202 nm for Pu2respectively, then the corresponding potential energy curves are calculated. For the ground states and the lowest energy excited states of U2and Pu2, their force constants, spectroscopic data and dissociation energies are obtained for the first time.
From the viewpoint of screen effect, penetration effect and polarization effect, the potential function of the Weakest Bound Electron Potential Model theory (abbreviated as WBEPM theory) is discussed. After deducing, the physical meaning of the effective potential suggested ithe theory is concluded that the first term in the potential function is the potential felt by thweakest bound electron in the central field of effective nuclear charge +Z′e, and the second term is the potential felt by the weakest bound electron in the dipole field produced by the polarizatio of the core composed of non-weakest bound electrons and nucleus.
The mechanism of the reactions Cl +HBr→HCl+Br and Cl+HBr→BrCl+H were investigated by density functional theory (DFT) at B3LYP/6-311G** level. All the transition states of reactions are validated by vibrational analysis. The rate constants of reaction from 50 to 1500K ware obtained by means of absolutely reaction rate theory using the acquired reaction activate energies and the partition functions of transition state and reactant complex in different temperatures.
The theoretical study on PuNn+( n= 1, 2, 3) using density functional method (B3LYP) shows that PuN+and PuN2+can be stable and PuN3+(5Σ、7Σ、9Σ) can not be stable. Ground electronic states are X5Σ+(PuN+) and X4Σ+(PuN2+),and their Force Constants and Spectroscopic Data have been worked out.
Atomiccharacteristicvalue(βi) isdefinedas:βi=( ni- 1) mi±hi. Thenovel connectivity index (mX) of atomic characteristic are set up with theβi, andmXbeing defined as0X=∑(βi)0.5,1X=∑(βi·βj)0.5. The0X(1X)values of 72 molecules for 4 series of hydrocarbon are calculated. It is found thatXwas highly correlated with the standard entropies and standard heat of combustion for these compounds. The results show that all the correlation coefficients are larger than 0.99. It has been demonstrate that the method is easy to compute, clear in physical meaning and convenient in applications. A modified jackknife test was performed to validate model robustness.
Surface(Enhanced Raman Spectra (SERS) of free(base tetraphenylporphyrin (H2TPP) and its Ag(, Mg(chelates (AgTPP and MgTPP) adsorbed on AgBr colloid were studied by 632.8 and 488.0nm excitation. The SERS results show that the adsorbed MgTPP (or H2TPP) molecules undergo silver(exchange (or silver(incorporation) reaction to form AgTPP. The chavge transfer mechanism is believed to be the major origin of Raman enhancement for both 632.8 and 488.0nm excitation lines. For 488.0nm excitation, additional mechanism of electronic pre(resonance effect also contributes to the Raman enhancement, resulting in a slightly different SERS spectra compared with 632.8nm excitation.
Low(temperature phase of GdBO3with triclinic form was prepared by Sol(Gel process, while only pseudo(vaterite form could be obtained from the conventional solid state reaction. The triclinic form will change to pseudo(vaterite structure when being heated at higher than 1000℃. Luminescence of the triclinic GdBO3:Eu indicated the existence of two different sites of the cations in the host, which were denoted as A and B in the work. Then site selective luminescence of the sample was investigated. The influences of concentration and temperature on the luminescence properties were reported. For high Eu3+concentration, a very strong interaction took place between the dopants. Emissions from the two sites were both strong and could not be separated. At low temperature and with a low concentration, selective luminescence from the two sites was obtained. Different energy transfer rates of site A→B and B→A were also observed.
Under different annealing temperature, Sm3+-doped SiO2gel and glass were prepared by sol-gel method and three-dimensional fluorescence spectra, excitation spectra and emission spectra of Sm3+in SiO2glass were measured. The results showed that the optimum excitation wavelength is 360nm, the strongest emission wavelength is 610nm, the excitation peak position are at 364, 393, 464nm, the emission peak position are at 578, 591, 595, 610, 732nm, which caused from, respectively,4G5/2—6H5/2,4G5/2—6H7/2,4G5/2—6H11/2transition of Sm3+. The effect of the Sm3+concentration on the emission intensity has been discussed, and the emission intensity of Sm3+became the stronger with increasing the doping concentration. The concentration quenching will occur when concentration of Sm3+exceeds 1.15%.
A new kind of organic-inorganic hybrid nanomaterial Polymer/MS/SiO2(M=Pb,Cd) have been prepared by incorporating sol-gel process and hydrothermal crystallization technique. The as-prepared polymer matrix and Si-O network can successfully control the morphology of semiconductor nanoparticles and prevent aggregation. The existence of polymer can reinforce the thermal stability of composites. X-ray powder diffraction was used to characterize the nanoparticles, and transmission electron microscopy was used confirm that semiconductor nanoparticles were dispersed homogeneously in the silica and polymer matrix.
Porous coralline hydroxyapatite (CHA) was produced by hydrothermal conversion of Porites skeleton (aragonite) at different temperatures and pH, with and without mineralizer KH2PO4respectively. X-ray Diffraction Analysis (XRD) and Scanning Electron Microscopy (SEM) were employed to characterize the phase composition and structure of products prepared under different conditions. The influences of temperature, pH and mineralizer on the hydrothermal exchange of porites into coralline hydroxyapatite were investigated
The superconducting ring-like property and the chiral effects of persistent currents intoroidal carbon nanotubes (TCNTs) are studied in this paper by using the electronic state energy formula of chiral TCNTs derived from the energy dispersion relation of the graphene sheet. When T=0 K, the persistent current of metallic and semiconductortype TCNTs is a linealy periodical function ofΦ, with a periodΦ0, but it is very sensitive to chiral angleθand toroidal radiusR. The persistent currents in chiral TCNTs are much stronger than in the achiral TCNTs. It also have been discovered that persistent currents decrease when toroidal radiusRincrease or temperature rise,and the decreasing rate depends the chiral angleθof TCNTs
A various of metal oxide nanomaterials were synthesized by arc-electrodeposition method in NaCl aqueous electrolyte, with different metal electrodes, under the voltage of 100V. The morphologies of the obtained nanomaterials were controlled successfully. The products were characterized by X-ray diffraction (XRD) and the XRD patterns were recorded with a Rigaku D/max-γA rotating anode X-ray diffractometer in the 2θrange 10o70o. The morphology and particle size of the products were investigated by transmission electron microscopy (TEM) and the TEM analyses were taken with aHitachi H-800 transmission electron microscope. From the results of XRD and TEM, it is obvious that different metal oxide products had different morphologies. The produced Fe3O4is spherical mixed by a few of rod-like product, ZnO is elliptic,γ-AlOOH is acicular and Mg(OH)2is acicular. It is apparent that the morphologies of the products obtained corresponding to different metal electrodes are greatly different from each other, under the same other experimental conditions. One can conclude from the TEM results that the products with different phase structures have different growth habits under the same experimental conditions, for example, the formation of tube-like Mg(OH)2may be closely related to the hexahedral structure of Mg(OH)2. It is very necessary to further study the relationship between the morphology of the product and the experimental conditions, especially the conditions for the formation of nanotubes.
The structures of oxidic and sulfided Rh-Mo-K/AC catalysts were studied by means of XRD and EXAFS techniques. Activities for mixed alcohol synthesis via CO hydrogenation were used to measure the catalytic properties of these catalysts. In the oxidic Rh-Mo-K/AC catalyst samples, there is strong interaction between Rh and Mo species, which may shift K2Mo2O7to MoO2. Molybdenum species are mainly converted into MoS2crystallites after sulfidation treatment, and the local ordered structure is shrunken with the increase in Rh loading. The incorporation of rhodium shows high performance of alcohol synthesis from carbon monoxide hydrogenation.
The nanosized BaTiO3powders modified with a layer of stearic acid were successfully prepared through the hydrothermal method and their microstructures were characterized. The results indicate that the products are of small crystal with small grain-size, narrow grain-size distribution and little agglomeration, meanwhile the polarity of the nanometer BaTiO3particles was greatly reduced and the powders had a better flowability. Because the surface of the nanometer BaTiO3powders was modificated with a layer stearic acid , which weakened the interaction between the particles of the powder.
The influence of pH, relative molecular weight and concentration of poly(acrylic acid) (PAA) on the viscosity of PAA solution was investigated. It was found that the rheology of PAA solution was closely related to the ionization and conformation of PAA chains. The increasing rigidity and the stretching of polymer chain resulted in a maximum viscosity at pH=8. The viscosity change of PAAsolution with addition of alumina powder was studied. It was found that the suspension viscosity reached its minimum when the amount of ceramic powder and PAA was at a certain ratio. At the same time, the viscosity minimum was also influenced by the particle size of powder.
The dynamic stability of Langmuir monolayers of stearic acid and 19, 21 - docosadiynoic acid (DDA) on different subphases at different surface pressure, oscillating frequency or temperature was instigated respectively by applying the VISCOS model on KSV LB-5000 Langmuir balance. It was showed that the lower the surface pressure or the oscillating frequency was, the more stable the monolayer was. Adding some metal ion into the subphase could also strengthen the stability of the monlayer.
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