2002 Vol. 15, No. 6

Article
A great interest has been recently devoted to the Van Vleck semimagnetic semiconductors which exhibit interesting magnetic and magneto optical properties. However, the far-infrared spectra in the Van Vleck semimagnetic semiconductors ZnSe∶Fe2+do not fitthe standardized crystal-field theory and in particular exhibit additional lines. The Hamiltonian matrices for the ground state5D of 3d4/3d6ions are derived by taking into account the cubic crystal field interaction the spin-orbit coupling and the dynamic Jahn-Teller effect, as well as the far-infrared spectra of ZnSe∶Fe2+are studied b using these matrices. The theoretical results being in good agreement with the experimental observations indicate that the far-infrared spectrum levels in ZnSe∶Fe2+, which do not exist for the standard crystal-field theory, are due to the dynami Jahn-Teller effect in this crystal. In addition, some theoretical Jahn-Teller splitting presented are in need of further theoretical and experimental studies. The presentmatrix is useful for the study of fine structure spectra, EPR parameters an dynamic Jahn-Teller splittings of 3d4/3d6ions in the cubic crystal field.
Taking Cl-anion as an example, the statistical thermodynamic theory of surface stress of anion adsorption monolayer on Au(111) has been established by using the lattice gas model. The effective pair interaction energy, the surface stress and the two-dimensional isothermal compressibility in chloride adlayer on the Au(111) electrode surface have been calculated. The calculational result of the surface stress of chloride adlayer is associated with the experiment. At lower Cl-coverage, considering the contribution of ClO4-, the change of surface stress is approximately linearly correlated with charge density. For the Cl-/Au(111) system, the difference between surface stress and surface tension is the same order of magnitude of surface stress, which can′t be neglected. Therefore, Haisset al.′s experiment results have been successfully explained by the theory.
Three hybrid density functional theory (DFT) methods (B3LYP (Becke′s three-parameter Hybrid Functional using the Lee-Yang-Parr Correlation Function), B3P86 and B3PW91 (Becke′s three-parameter Hybrid Functional with Perdew86 and perdew/Wang91 Correlation Functions respectively)) and two appropriate basis sets (6-311+G* and aug-cc-PVDZ) have been employed to investigate all the possible structures of the CO…CO+ coupling system on the global potential energy surface. The results show that there are three relative stable complexes verified by none imaginary frequencies. Among them complexes A and B are co-plane structures except complex C and the subtle difference between complexes B and C is the dihedral of them. Complex A is the most stable structure through the comparison of the energies of three complexes. The orbital binding character using the population analysis and covalent bond orders between atoms within the AIM methodology is also calculated at B3LYP/6-311+G* level. Then the precise interaction energies of the three complexes have been obtained through the corrections of the basis set superposition error (BSSE) and the zero point vibration energy (ZPVE), and the full counterpoise procedure (FCP) recommended by Boys and Bernardi has been applied for the BSSE correction. The results of the interactive energies are 252.47, 126.70, 127.12 kJ/mol for complexes A, B and C respectively, which are in agreement with the literature data reported before. Finally, we list the normal vibrational frequencies and corresponding IR intensity of the three complexes at B3LYP/6-311+G* level. Moreover, the analytical figure of normal vibration frequencies for complex A is also displayed at the same time. All computations indicate that the interaction between CO and CO+ is strong and DFT methods can serve as an effective tool to predict the molecular geometry, thermodynamics and frequencies that are well close to the experimental values.
The ground state geometrical optimizations of cyclic sulfur molecules S6~S20 have been studied with RHF/6-311G* and MP4/6-311G* ab initio methods, and are in agreement with the experimental conformations. The stable molecular structures of recent S14both experimental and theoretical are Cs symmetry and the bond parameters of optimizations are very close to those of experiments. S18(α) and S18(β) are two types of modification of S18ringwhich have been proved of the same stability due to their close energies. The polymorphic phase S20 of D4 point group has also been proved by calculating the structures and comparing the relative energies of D4with that of D2. Otherwise, The relationships of molecular conformation models with symmetries, dipole moments and vibrational frequencies have been discussed. The significant applications of cyclic sulfur have been deduced by studyingthe relations between their electronic structures and chemical reactivities.
The compounds hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octohydro-1,3, 5,7-tetranitro-1,3,5,7-tetrazocine (HMX) are two well known energetic materials. The Cyclopentamethylenepentanitramine is called CRX. The full geometry optimization and normal-mode analysis of CRX are performed using nonlocal density functional theory (DFT) method. The density functional used in this study is B3LYP and the basis set empolyed is 6-31G*. Normal mode analyses are used to characterize the stable point and to determine the harmonic vibrational frequencies. The standard thermodynamic properties (C0p,m, S0mandH0m) within 200~1200 K are calculated using the statistical thermodynamic method. The conformation of CRX is aboutC2symmetry. The dipole moment is 6.137 Dabye. C-N bond lengths and N-NO2bond lengths are among 0.144~1.48 nm, 0.139~0.142 nm, respectively. The difference between the energy of the highest occupied molecular orbital (HOMO) and that of the lowest unoccupied molecular orbital (LUMO) is 5.2054 eV, which predicts that CRX is more stable. All the thermodynamic quantities increase as the temperature goes up. This is because when the temperature is lower the main contributions to the thermodynamic functions are from the translations and rotations of molecules. But at the higher temperatures, the vibrations contribute more to their thermodynamic functions, which results in the increase of the thermodynamic functions. In addition, the added extent for both C0p,m and S0m decreases with the increasing temperature, but increases forH0m. Defined as the volume inside a contour of 0.001 electrons/bohr3density, the molar volume of CRX is computed, using the Monte-Carlo method based on the spatial structure obtained from full optimization at B3LYP/6-31G*level. The obtained molar volume is 200.499 cm3/mol. Then the calculated density is 1.846 g/cm3. It is greater than that of both RDX and HMX. The detonation velocity and pressure of the titled compound are predicted to be 9169 m/s and 37.88 GPa respectively by Kamlet formula. They are higher than those of RDX and HMX.
A two-phase repellent-translation equation of state of explosive detonation product (two-phase R-TEOS) was obtained. Using the two-phase R-TEOS and a known isentropic through the CJ point of an explosive as reference curve, the detonation parameters for various densities of the explosive can be estimated. The comparing the experiment data of detonation velocity for various initial density values of TNT which detonation product contains more solid carbon with the theory values estimated with above mentioned method, a new test of the hypotheses of the ZND theory was performed. The experiment and theory values of detonation velocity for various density values (from1.632 g/cm3to 0.901 g/cm3) are in good agreement, and their average relative difference is only 0.60%. The conclusion was drawn again that the hypotheses of the the ZND theory of detonation are true, and the two-phase R-TEOS is a proper equation of state of detonation product.
The reaction-flow-diffusion equation for low-concentration Brusselator is developed and the existence condition for differential flow-induced chemical instability for the model is theoretically analyzed by means of linear stability analysis and the method of steepest descent. The neutral valueФc of flow rateФof autocatalyticy and the group velocity v go perturbation wave packet are derived. The relations of flow rate Фto the perturbation growth rate Reλ is discussed. The temporal structure at different time τ (fixed Ф) and spatial structure with different Ф (fixe dτ) of the system while instability exhibits (Ф>Фc) is numerically studied, respectively. It is shown that the differential flow-induced chemical instability may exhibit and the perturbations propagate along the reactor in terms of periodic wave packet. It is proved that under the condition of low concentration for chemical reactions, the differential flow-induced chemical instability may also exhibit.
By means of the molecular dynamics simulation technique, the solidification process of liquid alloyAl3Ni and Ni3Al has been performed. The F-SN-body potentials have been adopted to describe the atomic interactions. The structural features have been revealed with the pair distribution function and bonded pairs analysis method. The variation of energy with the temperature and the relationship between the energy and the micro structure have also been studied. It has been concluded that the cooling rates have different influence on the final structure of Al3Ni and Ni3Al. The Al3Ni becomes the glass state at both of the cooling rates, but the short-order of the system has been strengthened at the relatively low cooling rate (4×1011K/s). The Ni3Al also becomes the glass state at the relatively high cooling rate (4×1013K/s), but crystallizes out at the relatively low cooling rate (4×1011K/s). At the same cooling rate (4×1011K/s), the Ni3Al melts of which Al is more than Ni crystallize out much easier than the Al3Ni melts.
Sr2GdRuO6 which is always used as a precursor in synthesizing superconducting cup rate RuSr2GdCu2O8, prepared by common solid state reaction in air or inO2is always accompanied by the formation of small amounts of ferromagnetic SrRuO3 impurities phase. It is reported in this paper that the pure phase compound Sr2GdRuO6 without any ferromagnetic SrRuO3 impurity phase is successfully prepared via solid state reaction in O2(or air)-water vapor mixed atmosphere. The pure phase compound RuSr2GdCu2O8 without any ferromagnetic SrRuO3 impurities phase is also obtained via analogous solid state reaction system using the pure phase compound Sr2GdRuO6 as a precursor. In addition, the mechanism of the solid state reaction in the presence of water vapor is also discussed. It suggests that the vapor is not beneficial to transformation of SrRuO3 to Sr2GdRuO6, and the effect of water vapor on the solid state reaction is to suppress the formation of SrRuO3 due to the formation of RuO2·nH2O in the water vapor atmosphere.
The step and approach of specimen making for freeze-etching replication transmission electron microscopy (FERTEM) that was used for the in-situ observation of in-situ synthesizing nano-dispersion system were studied. The diameter, diameter distribution and conglomeration behavior of nano particles in foursorts of dispersion system were observed by FERTEM technique. The results indicated that the image qualityof transmission electronmicroscopy was closely related to the freeze-ecthing time, and the freeze-ecthing time should correspond to the content and diameter of nanoparticles in the dispersion system. The FERTEM technique provided a reliable means for thein-situ observation of the non-aqueous nano-dispersion system, and can collect manifold information simultaneously.
To find a new system of self-assembled monolayers (SAMs) and to build up new founctions, the SAMs of heterocyclic selenium compounds (piaselenol, with macrocyclic conjugated plane molecule structure) on gold surface were investigated. The SAMs of piaselenol were characterized by X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry. The results of XPS showed that the binding energy of Se3d changed from57.4 eV to 57.1 eV, which proved that the gold surface had been assembled with piaselenol molecules. The results of cyclic voltammetry showed that the peaks of the oxidation and reduction of Fe(CN)63-/4-almost disappeared after the self-assembly. The reduction peak potential of the self-assembled piaselenol on gold was -0.66 V in the Na2B4O7solution, which was close to the potential of bare gold in piaselenol solution. The electron transfer mechanism about SAMs of organoselenium compounds on the gold surface was also discussed.
Nanoscale TiO2 was used as the photocatalyst in the oxidization process of methanol, formaldehyde, and formic acid with the 0.1 mol/L aqueous solution respectively. 60 mL of HCH2OH, HCHO and HCOOH with 0.1 mol/L was put in a glass tube reactor respectively with 0.2 g nanoscale TiO2 oxygen flowed into the reactor with the 60 mL/min from the bottom. An Hg lamp with 364 nm as the main wavelength generated UV light at 25~28℃. And the irradiation lasted 10 h. The final product CO2 and the decreasing reactant were detected by the thermal conductivity detector (TCD) and the hydrogen flame ionization detector (FID) of gas chromatograph respectively. From the change of the concentration of the reactant and CO2, the reaction order of the group was zero order respectively. And the Langmuir-Hinshelwood Equation also confirmed the conclusion. Formic acid was the easiest one to be oxidized and methanol was the most difficult one to be oxidized. TiO2 was characterized by TEM, XRD, SSA and XPS respectively. The micro crystal of TiO2 is mainly anatase characterized by X-ray diffraction (XRD) and its average particle size is about 15 nm from the TEM image. The specific surface area of TiO2 has some reduction after irradiation. Formaldehyde and formic acid were found on the surface of TiO2 after the reaction, which showed that formaldehyde and formic acid were the intermediates of methanol during the photocatalytic reaction. The XPS of TiO2 after reactions showed that the mechanism of oxidization methanol should be: methanol was oxidized to be formaldehyde firstly, then through formic acid, until CO2 and H2O appeared.
A novel oil-soluble C60 -dodecyl acrylate copolymer was synthesized. The resulting product was characterized by means of Fourier transformation infra-red spectrometric and ultra-violet-visible spectrometric analyses. The frictional behavior of oil-soluble fullerene copolymer was studied for the first time. Its tribological characteristic as lubricant additive in liquid paraffin was studied with a four-ball machine and a scanning electronic microscope. The results form four-ball tests are given as follows. ① The wear scar diameter obtained with liquid paraffin containing fullerene copolymer is related to the content of the fullerene copolymer. With the increasing of the fullerene copolymer content,the wear scar diameter is decreased. When the content is between 0. 5% and 0. 75%,the wear scar diameter is minimum. Then excessive fullerene copolymer results in an increasing of wear scar diameter. ② With the increasing of friction time,the wear scar diameter obtained with liquid paraffin containing 0. 5% fullerene copolymer under a load of 200 N increases also. After 20 min rubbing,the wear scar diameter doesn't increase any more. By comparison,the liquid paraffin under the same conditions gives larger wear scar diameter,especially after 20 min rubbing,the difference in wear scar diameter between two lubricants becomes larger. SEM shows that the wear scar obtained with liquid paraffin containing 0. 5% fullerene copolymer under a load of 100 N and a testing time of 30 min is obviously smaller and exhibits mild scratches,but in comparison,larger wear scar and serious adhesive wear were observed in the presence of liquid paraffin under the same conditions. In a word,the addition of a certain amount of C60 -dodecyl acrylate copolymer can improve the antiwear properties of liquid paraffin and the micro wear conditions of the frictional pair.
That the activity coefficient of mixed electrolyte solution is determined using ISE has become a simple and practicable method. There are a lotofNa+、K+、Cl-、SO42-and a little Ca2+in the seawater and saline. The study of these ionic mean activity coefficients is very important in the designing and exploiting technology for the industry of producing salt, seawater desalinization and so on. The object of this text is the ternary system of NaCl-KCl-H2O at 35℃. The experiment device of determining the ionic average activity coefficients of electrolyte solutions has been set up. The electromotive force of pure NaCl and KCl aqueous solution has been determined using the ion selective electrode at 35℃. The electrode constants have been regressed. The mean relative error about the activity coefficient of KCl solution is 0.9% between the calculated value of Pitzer equation and the calculated value of regression. The mean relative error about the activity coefficient of NaCl solution is 1.5% between the calculated value of Pitzer equation and the calculated value of regression. The linearity connection of the electromotive force vs the logarithm value of activity is very good within the experiment concentration. This indicates the determination method and the experiment equipment are reliable and the determined data are believable. The ionic average activity coefficients of NaCl and KCl have been determined in the ternary mixture systemofNaCl-KCl-H2O at 35℃ using the ion selective electrode. The concentration of the mixed electrolyte solutions is 0.1~1.5 mmol/L in six groups altogether. The interaction parameters of the Pitzer equation have been regressed. The maximal relative error between the experiment value and the calculated value is 5.6% and the mean relative error is 2.3%.