2002 Vol. 15, No. 1

Article
The rotational spectra of the nascent NO(X2 Πv″=1,2,3) product from the photolysis of nitrosobenzene(C6H5NO)have been recorded by using the single-photon laser-induced fluorescence (LIF) technique. The rotational temperature and the relative ratio of vibrational population of the nascent NO(X2 Π) photofragment were obtained by probing the internal-state distribution of the fragment. The energy disposal in the photodissociation of nitrosobenzene at 266 nm was studied. In contrast to small molecule, the large-size molecule C6H5NO, gives rise to a broad-energy distribution involving all degrees of freedom in photodissociation.
CCl2was produced by dc discharge of CCl4seeded in Argon gas with a ratio of 1/50. Laser induced fluorescence excitation spectrum of CCl2~A1B1-~X1A1between 440~580 nm has been measured under the supersonic free-jet conditions. The K-structures of (v1, v2, v3)-( 0, 0, 0 ) bands were clearly resolved and assigned to 722 subbands. The vibrational frequencies,ω1=631.20 cm-1,ω2=302.00 cm-1, andA′-B′=3.476 cm-1in the excited state were obtained.
Carbenes are important reactive intermediates in a variety of chemical reaction, and therefore have been extensively studies both experimentally and theoretically to explore their chemical properties and various parameters that affect their stabilities. In order to stabilize triplet carbenes kinetically to extent that they are able to survive under normal conditions, we attempt to protect the carbenic center of triplet diphenylcarbenes by introducing a series of substituents at the ortho position, and revealed that it is very effective on the stabilities of triplet diphenylcarbenes to introduce the big and unreactive substituents at ortho position. But this method has been limited that diazo compounds are used as precursor of carbenes and the preparation of diazo compound becomes more difficult as the bigger substituents are introduced in the ortho position. For this reason, the other approach, that the electronic (thermodynamic) effect of para substituents on the stabilities of triplet diphenylcarbenes, has been considered. To explore this effect, a series of triplet di(2,6-dimethylphenyl)carbenes (2) bearing symmetrical para strong electronic disubstituents have been generated by the irradiation of the corresponding diazo precursors and studied by means of electron paramagnetic resonance (EPR) spectroscopy. The zero field splitting parameters, DandE, were measured in matrices of different viscosities and were analyzed with molecular structures in terms of a scale of spin-delocalization substituent constants. And studied the stabilities of triplet di(2,6-dimethylphenyl)carbenes (2) by measuring the disappearance temperature of (2). Finally we have measured the life-time of the triplet di(2,6-dimethylphenyl)carbenes (2) by laser flash photolysis (LFP). It was showed that the triplet di(2,6-dimethylphenyl)carbene having stronger spin delocalized substituent have more line structure and show more stability.
The amorphous alloys are a kind of interesting and promising material in material science. Owing to its special structural character and electronic properties, it provides a path to novel, more active and selective catalysts. Although experimental works on amorphous alloy could be found everywhere, a few theoretical calculations were published in literatures. It does give a challenge to theoretical researcher since it is not easy to model the amorphous structure. Until now, a controversy of the direction of charge-transfer still exists in the study of the Co-B amorphous alloy. According to the experimental results, the charge transfer between Co and B in Co-B amorphous alloy is from B to Co, which seems to be incompatible with the electronegative view in classical chemistry. On the other hand some theoretical calculations showed an opposite conclusion to the experiment. Since many physical and chemical properties like specific heat, magnetic susceptibility, ferromagnetism, superconductivity and catalytic activity are directly related to the electronic properties of the local structure of amorphous alloy, in this case, the charge transfer between Co and B are required to clarify the argument. The previous calculations were, unfortunately, not complete in many aspects; at the very least, the calculated models and methods were too rudimentary. The aim of our present paper is to investigate the electron transfer between B and Co of Co-B amorphous alloy by a series of cluster model ComB2(m=1~4) and Co-B calculations with density functional theory (DFT). Since most of the modeling and simulation concerning amorphous alloy were based on statistical method, which lays emphases on the long-range disordered, they give little information of electronic properties. In order to understand the electronic properties of amorphous alloy in detail, the best way is to calculate it by using a proper model with a correct local structure referring to the experimental fact at the precise level of quantum chemistry calculation. Hence, the present work tries to use a kind of new models. The models are constructed according to the following experimental results: amorphous alloy are packed by small clusters, its local structure is in ordering, and the metal-metalloid is chemically bonded. Our present paper, considering the direct B-B contact in cluster model is the key point that makes our calculations differ from the previous theoretical works. The results of the calculations showed that boron is an electron-donor, while cobalt is an electron-acceptor, which agrees well with the experimental results. It is very possible for Co-B amorphous alloy to exist the direct B-B contact. Compared with the calculation results from another series of ConB(n=1~4) cluster models, It could be concluded that the ComB2(m=1~4 ) clusters is more reasonable for the structure of Co-B amorphous alloy.
Three density functional theory approaches: the local-spin-density approximation Slater-VWN functional, the gradient-correction Becke88-LYP functional and the hybride Becke3-LYP functional are used in the geometry optimizations and frequency calculations on Asn(n=2~5) clusters and their anionic clusters, with 6-311+G(3df) basis sets. Several possible structures for each cluster sizenof neutral and anionic clusters have been investigated. Their equilibrium structures have been found. The equilibrium structures of neutral Asnclusters obtained in the present DFT calculations are compared with other theoretical results in literature and experimental data. The agreement between them is very good. The equilibrium structures of anionic Asn-clucters are predicted. The most stable structures of anionic Asn-(n=3~5) clucters determined by DFT calculations are as follows: a isosceles triangle (C2v) forAs3-, a roof-type(C2v) forAs4-, a pentagon(D5h) for As5-. These most stable structures of anionic Arsenic clusters are similar to those of anionic clusters formed by other group V elements including P, Sb, Bi. The adiabatic electron affinities (EAa) of these arsenic clusters are also calculated,which is in good agreement with the experimentalEAavalues of Asnclucters from the work by Lippaet al.The present theoretical study shows that Jahn-Teller effect is very obvious in determining the stable structure of Arenic clusters. In the D3hstructure of As3, the Td structure of As4-, and the D5hstructure of As5, the highest occupied molecular orbital(HOMO) for one structure in the ground state is all degenerate. These degeneracies result in Jahn-Teller distortions and make these structures with high symmetries unstable.
CaTiO3is widely used in electronic ceramic materials, it is also a key component of Synroc, a synthetic rock form used to immobilize nuclear waste. There has been considerable interest in the structure phase transitions of this typical perovskite oxide. As reported by Kennedyet al., CaTiO3is orthorhombic with space group Pbnm below 1380 K and belongs to another orthorhombic space group Cmcm between 1380 K and 1500K. At 1500 K, it transforms into tetragonal with space group I4/mcm. Above 1580 K, it becomes cubic with space group Pm3m. Lemanovet al.measured the dielectric properties of CaTiO3at low temperature, and classified it as an incipient ferroelectric or a quantum paraelectric. CaTiO3is called a“higher”quantum paraelectric because its dielectric constant saturates at higher temperature than that for other quantum paraelectrics such as SrTiO3and KTaO3. To understand the physics underlying these properties, first-principles calculation of the electronic structure is desirable. In order to understand the tendency of the CaTiO3cubic perovskite to suffer a ferroelectric transition, we calculated the electronic properties of CaTiO3for different displacement of Ti in the [001]direction. At the experiment equilibrium volume (V/ V0=1.0), CaTiO3is not energetically favored with the proposed ferroelectric distortion. However, with a 10% volume expansion(V/ V0=1.1), the same displacement results in a shallow, but well defined double well. It implies that there is a tendency to ferroelectricity in cubic CaTiO3crystal. This is consistent with the experimental results that point out that CaTiO3is an incipient ferroelectric. From our calculation, the ferroelectric state can be induced by a negative pressure.The DOS of Ti d and O p atΔz=0.03 for V=V0shows there is a weak hybridization between Ti d and O p. While for a 10% volume expansion, this hybridization becomes stronger. Like other perovskites, it is this hybridization between Ti 3d and O 2p that weakens the short range repulsions and stabilizes the ferroelectricity. The strong hybridization implies that the interaction between Ti and O is highly covalent. This is consistent with the analysis of the total energy. From the calculated total energy, it is shown that CaTiO3has a tendency to a ferroelectric state in which the atom Ti displaces in the [001] direction. An analysis of the DOS and electric field gradients reveals that there is a hybridization between Ti 3d and O 2p. This hybridization is essential leading to the incipient ferroelectricity.
The formulas of inner pressure and excess inner energy of the liquid mixture are derived using distribution function theory. During the derivation three characters of interaction potential energy of the liquid mixture are assumed. The first is that the interaction force between molecules is the short-range force. The second is that the many-body potential is only relying on the distances between the molecules. The third is that the potential energy of the liquid mixture can be written as the sum of a series of many-body potential . The inner pressure and inner energy of the liquid mixture can be expressed in the power series of the volume. The coefficients in the series are expressed in many-body potential and radial distribution functions and are only depend on temperature. The expression of the inner pressure and excess inner energy of pure liquid are discussed. The excess inner energy and inner pressure are agree with the result of Egelstaff′s perturbation theory and Frank′s experiment respectively in two special situations. Two special cases of the liquid mixture are discussed. One of them is that a method to prove the mixing law of the excess inner energy of the liquid mixture in special situation. The other is that the expressions of excess inner energy and the inner pressure have the same form with the result of Frank′s experiment.
Absorption loss due to high harmonics of C-H vibrations, the primary loss factor in PMMA POF, was analyzed and calculated. And the results were consistent with measured datas. The mechanism that deuterating and fluorinating could decrease loss of POF was theoretically approved. Absorption wavenumber and loss of streching vibration and bending vibration of different quantum number were obtained. With increasing of wavelength, absorption loss due to high harmonics of C-H vibrations increased and absorption loss of stretching vibration was higher one order of magnitude than that of bending vibration, and both was in proportion to quantum number respectively.
The compound octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine is a well known energetic material called cyclotetramethylene-tetranitramine (commonly known asHMX in the explosives field). It is an eight-numbered cyclic nitramine with best comprehensive properties and with applications ranging from explosives and rocked propellants to automobile air bags. It is unusual among high explosives as it has four readily formed and well-recognized polymorphs.β-HMX is the thermodynamically stable from under ambient condition. Despite the many experimental investigations, very few theoretical studies have previously been reported for HMX. The high accurate calculation for HMX has been carried out based on ab initio quantum mechanics. Geometry optimization and normal-mode analysis of HMX inβform are performed using nonlocal density functional theory(DFT) method. The density functional used in this study is B3LYP and the basis set employedis 6-31G*. Normal-mode analyses are used to characterize the stable point and to determine harmonic vibrational frequencies forβ-HMX conformer. The molecular geometry, electronic structures, IR spectra and thermodynamic properties are obtained. The fully optimized geometric parameters and the net electric charges on atoms all have Cisymmetric property. C-N bond lengths are among 0.144~0.148 nm. This indicates that all cyclic C-N bonds are single bond. The N-NO2bond Mulliken population is the smallest among the bonding atoms. The fact indicates that there are less electronics between them and predicts that this bond is an initial bond for pyrolysis and explosive. The IR spectra are in good agreement with the corresponding experiment data. Half of the 78 harmonic vibrational frequencies forβ-HMX are IR active and belong to Au representation, the rest are Raman active and belong to Ag representation. The calculated standard thermodynamic functions, heat capacities at standard conditionC0p,m, standard entropySm0and standard enthalpyHm0between 298~1200 K increase with the increasing temperature. These functions are helpful to further study on the reaction and properties forHMX.
Mixed oxides, Ti02-MeOx (Me-V, Cr, Mn, Fe, Co, Ni, Cu) have shown high catalytic activity for the NH3 decomposition reaction and the reduction of SO2 by NH3 to elemental sulfur. Co3O4-TiO2 and Fe2O3-TiO2 catalysts show higher catalytic activity than other catalysts at low temperature. Characterization by XRD indicates that transition metal sulfides are probably the most active. The mechanism of the reduction of SO2 by NH3 to elemental sulfur over Ti02-MeOx (Me-V, Cr, Mn, Fe, Co, Ni, Cu) catalysts is assumed.
Multi-walled carbon nanotubes with diameters of 20~30nm were synthesized by cobalt-catalytic decomposition of acetylene, which are showed by TEM images. A series of pretreatments including purification, annealing and doping were performed before carrying out hydrogen storage experiments at room temperature and modest pressure (12 MPa). For comparison, the annealing treatments were processed under ambient pressure in air and nitrogen atmosphere respectively. KNO3solutions (0.1 mol/L and 1.0 mol/L) were used to dope carbon nanotubes. The results suggest that both annealing and doping play an important role in the hydrogen storage capacity of carbon nanotubes. Under the same conditions conducted, MWNTs annealed in nitrogen adsorbed more hydrogen than those annealed in air. FTIR spectra of the samples shows that the amount of oxygen functional groups linked to MWNTs after annealed in air is more than that treated in nitrogen. The former treatment may bring about more agglomeration of MWNTs, decrease the specific area and surface activity of MWNTs and eventually lead to lower capacity of hydrogen adsorption. The results also show that with the same dopant, the capacity of hydrogen adsorption has great difference when the concentration of the doping solution changed. Hydrogen adsorption of MWNTs increased not only after doped in KNO3solution but also with the increase of solution concentration in certain extent. An optimal result(3.2%)was obtained when carbon nanotubes were annealed in nitrogen at 500℃and doped in 1.0mol/L KNO3solution. Hydrogen desorption experiments were also carried out at room temperature. It is found that after a typical adsorption/desorption cycle under ambient temperature, the MWNTs samples still retain significant amount of stored hydrogen. The phenomenon may be attributed to the existence of two types of adsorbed hydrogen in the structure: physical and chemical adsorptions, the former can be released easily and the latter is strongly bound and could be released more difficultly.
Surface modified (NH4)3PMo12O40nanoparticles were synthesized in a mixture solution of waterethanol with cetyl trimethyl ammonium bromide as a modification agent. The structure of nanoparticles was characterized by TEM, XRD, FTIR, DSC, TGA, etc., and their tribological properties as additives in liquid paraffin were investigated with a four-ball tribometer. In the preparation process, Na2HPMo12O40·14H2O was previously synthesized according to a literature. Firstly, ammonium chloride and cetyl trimethyl ammonium bromide were respectively put into the mixture solvent of distilled water and ethyl alcohol in a flask with stirring, then, the solution of Na2HPMo12O40·14H2O was dropped into the flask, immediately, a yellow precipitate was produced. After 1 h of continuous stirring and 12 h of standing, the yellow precipitate was collected by filtering and was rinsed with alcohol and water, individually, desiccated at room temperature. The yellow powder (marked as sample a) was the expect surface modified (NH4)3PMo12O40nanoparticles. Non-modified (NH4)3PMo12O40particle (sample b) was prepared with the same procedures as above, except that cetyl trimethyl ammonium bromide was not used. The dispersity of sample a and sample b were evaluated in solvents such as chloroform、benzene、liquid paraffin, and distilled water, at room temperature. The results show that sample a disperses in organic solvents, but it doesn′t disperse in water, and sample b doesn′t disperse in organic solvents or water. It indicates there are organic groups on the surface of sample a. TEM graphic shows that the mean graininess of sample a is about 20 nm, and the average grain-size of sample b is over 1μm. This suggests that the modification agent can restrict the congregation of (NH4)3PMo12O40nano-cores. The FTIR absorption spectra of sample a indicate that (NH4)3PMo12O40nanoparticles have a Keggin structure, and confirm the existence of organic groups. The XRD pattern confirms there are (NH4)3PMo12O40nano-cores in sample a. The DSC and TGA curves of sample a show the decomposition temperature of (NH4)3PMo12O40nano-core is about 300℃. The tribological tests show that the synthetic nanoparticles as additive in liquid paraffin improve the antiwear and friction-reduction ability of the base oil, and the most appropriate additive concentration is 0.25 %. According to our inference, this is attributed to the generation of a surface protective film, by way of tribochemical reaction.
Quantum-sized Titania and SnO2-doped Titania were prepared by Sol-Gel method. After heat treatment at different temperatures, powder samples with different sizes (3~12 nm) were obtained. These samples were characterized with X-ray diffraction, eletron diffraction and reflect spectrum. Experiment shows that doped SnO2promotes the anatase→rutile phase transformation process, and reduced the temperature of phase transition. The doped SnO2restrain the growth of nano crystals of TiO2. Quantum-size effect of nano-Titana was observed. But shift of optical absorption edge was not so apparent when concentration of SnO2changed. Probable reasons were discussed.
The impedance and photoelectrochemical properties of titanium oxide film formed by direct thermally oxidation of titanium were investigated by electrochemical impedance spectroscopy, photocurrent response etc. The results showed that the charge transfer resistance of interfacial decreased, while photocurrent increased gradually and the photoelectrocatalytic degradation rate of aniline increased with increasing the oxidation temperature. The photoelectrochemical performance of TiO2electrode decreased sharply when the oxidation temperature was higher than 600℃. There had good correlation between the structure of catalyst, charge transfer resistance of interfacial, photocurrent and photoelectrocatalytic degradation rate of aniline.
With the technology of multiarc ion plating, the experiments of TiN membrane-plating on the different base materials are carried out, which fabricate TiN/Fe, TiN/Cu and TiN/Cr/Cu compound membranes. The appearances, structures and surface characters of the contact interfaces of TiN and three different underlays, which are Fe, Cu and Cr/Cu, are obtained with the help of the SEM, XRD and XPS. The observation of SEM shows TiN coating and Fe, Cu of Cr/Cu base materials can form the well-distributed and flat contact interface under the certain ion membrane-plating condition. At the same time, there is an apparent interface on the copper material and the obvious distribution of sandwich micro crystallization. The analysis of XRD manifests the membranes shaped on Fe, Cu and Cr/Cu surfaces all contain the heteromorphism such as TiN, Ti2N and so on. It also demonstrates there are some Ti-Cr metal compounds on the Cr/Cu interface. The result of XPS shows the surface also form TiO2and TiOxNyoxidizing membranes besides TiN membrane. After Ar+ etching for five minutes, TiO2disappears, and TiOxNydecreases while TiN increases. The interface of TiN and Cr/Cu shapes palpable Ti-Cr and Cr-Ni mutual diffused layer which is helpful to enhance the adhesion force of membrane and shape firm TiN coating.
Various superacid SO42-/ZrO2-Al2O3catalysts were prepared by a coprecipitation, and modified by aging at low temperature and addition of the rare earth oxide, such as La2O3. A optimum atomic ratio of Zr/Al was found to be 0.5, which was confirmed by the catalytic activity of samples forn-butane isomerization . IR measurements demonstrated that the intensity of the peak at 1393cm-1for the samples aged at low temperature and containing the rare earth oxide was more higher than that for the samples at room temperature. For the sample containing the RE oxide and aged at low temperature, XRD observed a metastable tetragonal phase of ZrO2crystal which is responsible for the higher catalysis activity as we believe. The observation of catalytic activity for esterification of sucrose further evidenced the conclusion mentioned above.