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1989 Volume 5 Issue 3
The results of the moleoular dynanmics simulation of LiCl melt indicate the existence of microscopic holes in molten salt. Some holes are of size comparable to that of Li~+ ion and Cl~- ion. In order to describe the holes in melt better a modified Bernal model has been proposed, in which the centre of the hole with diameter equal or larger than that of Li~+ or Cl~- ion is considered as centre of "virtue" particle, and takes part in the construction of Voronoi polyhedron. It can be seen from our calculation: 1, the Voronoi polyhedron in LiCl melt is more complex than that of the simple liquid; 2, the Voronoi polyhedron of Cl~- ion is more complex than that of Li~+ ion; 3, the face of the Voronoi polyhedron can be observed clearly in the Voronoi polyhedron of Cl~- ion; 4, the Voronoi polyhedron of hole with the diameter near equal to Li~+ ion is more complex than that of Li~+ ion, while the Voronoi polyhedron of the hole with the diameter equalto that of Cl~- ion has the similar geomitrical behaviour as that of Cl~- ion. The reason of above phenomena is discussed briefly.
The superconducting phase Tl_2Ca_3Ba_2Cu_40_(12), with Tc=108K and Meissner effect 66%, has been prepared. The unit cell is body-centred tetra nal, space group D_(4h)~(17)/mmm, lattice parameters a=0.3854(1)nm, c=4.2070(11)nm. In crystal two structural units{(O_2Cu)(BaO)(TlO_2Tl)(OBa)(CuO_2)}are separated by two CaCuO_2 slabs. Also, the relation between c axial increment and Tc in double Tl-O layer system is discussed.
The local structure and bond-orientational orders in molten salt LiF, KCI, LiF, and LiCI systems have been studied by molecular dynamics simulation. The bond spherical harmonics have been calculated for the computer-generated instantaneuos configurations of the molten salt systems. A new method, i.e. the method of bond spherical harmonics statistics under equal neighbor number N, has been proposed. For the standard structures with different coordination number, their quadratic invariant Q_l histograms under same N have been calculated and a model with a parameter of square deviation have been suggested. Comparing the Q_l from molecular dynamics simulation with the standard Q_l from linear combination of two standard structures, it can be found that the local structures in those four molten salt systems are near to tetrahedron more or less and the icosahedron structure is hardly found. The results showed that the fractions of tetrahedron local structure increase as the ratio r_+/r_- of cation radius r_+ to anion radius r_- decreasing.
The local structure of quenching process of lithium chloride has been studied by molecular dynamics simulation. The sequentially-quenched model was adapted. When the equilibrium reached at the melting point 878 K, the system was fastly quenched to 698 K and then the system relaxed to equilibrium. The process was repeated as above and the system was quenched to 498 K, 298 K, and 198 K, respectively, We calculated the quadratic invariants Q_l histograms at different temperatures by averaging the Q_l values of theinstantaneous configurations with the method of fond spherical harmonics statistics under equal neighbor number. Consulting the Q_l histograms of the linear combination model with a parameter of square deviation in which model the local diamond structure was predominant, we found that the Q_l histograms from the model and those from the simulation were very similar. The results showed that in the quenched LiCl system the local orientation obviously tended to be binary diamond structure (like GaAs) and the square deviation in model would be decreased with the lowering of simulation temperature.
The electrolyte solution consisted of 1.5 mol.L~(-1) HCl and 0.2 mol.L~(-1) o-methylaniline was electrolysed at a constant potential by using two pieces of platinum as electrodes, the anodic potential was controlled at 0.4V(vs. SCE). A blue and cohesive film was formed at the anodic electrode, it was poly-o-methylaniline(poly-o-toluidine). Its ESR spectrum was characterized as a single narrowline. When a fresh synthesized poly-o-methylaniline(0.35V) was reduced to -0.22 V(vs.SCE), its conductivity decreased from 5.8×10~(-3) to 3.5×10~(-5) S.cm~(-1), and its peak-to-peak linewidth ΔH_(p-p) increased from 1.94 G to 3.10 G. The film colour changed with the pH values of the solution and its electrode potentials. There are two anodic and two cathodic peaks on the cyclic voltammograms of poly-o-methyl-aniline in the 1.5 mol.L~(-1) ZnCl_2 of pH 1.69, the anodic and cathodic peaks at more positive potentials shift toward the negative potentials with increasing pH values. At pH 3.89, only one anodic peak and one cathodic peak on cyclic voltammograms are remained. The peak potentials and peak currents of poly-o-methylaniline in the different pH values are independent of cycles.
The NMR relaxation studies give information about both the dynamic behavior of adsorbed molecules and the physical properties of the adsorbent, such as specific surface and pore size distribution. The aim of this work is to study the adsorption state of benzene and cyclohexane on charcoals with various pore structures. The physical properties of charcoals studied were given elsewhere. Spin lattice and spin spin relaxation times(T_1 and T_2)were measured on a Varian XL-200 spectrometer by inversion recovery and CPMG spin echo method respectively.
The ln(M_0-M(t))/M_0)-t relation for a single exponential decay is a straight line but for biexponential decay it is bent (Fig.1). Experimental results show that the magnetization of liquid benzene decays exponentially while molecules adsorbed on charcoals obey the biexponential decay rule (Fig.2). Simulation of the magnetization decay curves gives two groups of relaxation times and their relative amounts (Tab.1 and 2). The rapid relaxing molecules (T_(1s)~1-2 ms) are solid-like adsorbed on the solid surface, while the slow relaxing molecules (T_(1v)~0.1-1.0s) are liquid-like condensed in the capillaries. The volume of the solid-like adsorbed layer can be obtained by mutiplying the relative amount of these molecules (M_(0s)/M_0) by the adsorption capacity of the charcoal, and the thickness of this adsorption layer by dividing this volume by the specific surface ares (Tab.2). This thickness ranges from 0.10 to 0.16 nm for all of the charcoals studied.
The calculated thickness of the adsorbed layer from ~(13)C T_1 data agrees well with those obtained by ~1H T_1 measurements (Tab.3).
~1H T_2 are also biexponential (Tab.4) and depend on charcoal species.
The adsorption isotherms Of polyethylene glycols (PEG, molecular weights of 400, 1000, 3350, 6000 and 20000), one polypropylene glycol (PPG) and polyoxyethylene-polyoxypropylene block co-polymers (L61, L64 and F68) from water onto silica gel have been determind (at 25℃). Except polypropylene glycol,all the other isotherms can be represented by the Langmuir equation. The calculated results show that for PEG and EO-PO co-polymer the molecular area at limiting adsorption (A) versus the number of EO in the polymer molecules (n_(EO)) is a curve which does not through the origin, If the PEG molecular weight>3000, the A-n_(EO)) curve is approximately a straight line through the origin. On the basis of these results and the cosideration of adsorption of water, it is suggested that the adsorbed molecules lies flat on the surface of silica gel.
Three kinds of chemical modified silica gel, Si-O-C_(10)H_(21)-n(Ⅰ), (Ⅱ) and Si-O-SiMe_3 (Ⅲ), were prepared. Fluorescence and lifetime of pyrene on these silica, gel were investigated. Exeimer emission of pyrene was formed from two pathways, excited groud state aggregate and excited monomer with groud state monomer. Groud state aggregate on silica gel Ⅲ was more than on silica gel Ⅰ in same concentration. Pyrene was dispersed as monomer in wide range coneentration when chemical modified silica gel adsorbed 1-decanol and excimer formation was controlled predominantly by dynamic process. Activated energy of excimer formation is 7 kcal.mole~(-1). Effect of temperature on fluorescence and lifetime of pyrene was studied. Effect of topochemical environment on fluorescence vibrational structure of pyrene was discussed.
OOD-RMPI spectroscopy Of ammonia using the fast predissoeiating à state as the intermediate has proved to be a feasible approach to uncover hidden spectroscopic information on both the upper electronic states and the intermediate predissociating species. The rotationally resolved MPI spectra of NH_3 and ND_3 X→(2hν_1)Ã→(hν_2)C′transition and correspondingly the rotational constants of ND_3 C′ ~1A_1′(v_2=0,1) haStebeen obtained. We found that only Q branch lines of NH_3 X→à 2-photon transition appeared when linearly polarised pumping light was used. At a series of different v_1 frequences, we can always get 2v_1+v_2 resonant with a fixed X→C′rovibronic transition line by tunning v_2. The intensity envelope of the ion signal thus obtained represents the rotational line profile of à state. From the width of the profile predissociation life time of à is obtained.
The excess volumes and volume excess refractive indexes have been measured over entire composition range at 293.15 and 298.15K for tetrachloromethane+1-methyl-2-,pyrrolidinone, +cyclopentanone, +pyridine, +2-butanone, +1-pentanol, + 2-propanol, or+methylcyclohexane. The results show that V_E for CCl_4+C_5H_9NO, +C_5H_8O, + C_5H_5N are large negative value. It is attributed to a chargetransfer interaction between tetrachloromethane and the second components. The excess volumes for (CCl_4+C_5H_9NO) are the largest negative, its minimum value is -1.19 cm~3.mol~(-1) at 298.15 K. The V~E for CCl_4+(CH_3)_2CHOH, +C_5H_(11)OH are positive or slight negative, suggesting that there is not the specific interaction between tetrachloromethane and alcohol molecules.
We propose a semi-empirical formula for predicting excess volume of binary mixtures on volume excess refractive index. The resnlts are satisfactory.
The electronic structures of [Cu(piotn) (H_2O)2]~(2+) and [Cu(pioen) (H_2O)_2]~(2+) ions,where piotn is N,N′-trimethylene bis(N-oxopicolinaldimine) and pioen is N, N′-ethylene bis(N-oxopicolinaldimine), have been calculated by CNDO/2 method.Using the change of atomic net charges and formation of dolocalized π bond, we explain the directions of wave number shifts of ν_(N-O) and ν_(C=N) in their infrared spectra after the complexes have been formed.
The oscillation reaction in itaconic acid-BrO_3~-Mn~(2+) investigated. This paper deals with the behavior of this oscillating reaction. The absorption of light at the two wavelengthe λ=310 nm and λ=475 nm oscillated in phase. A mechanism for this oscillating reaction was suggested. The mechanism is composed of three main processes:Process A: Consumption of bromide and formation of Br_2IA. Process B: Autocatalytic formation of bromous acid with a rapid oxidation of Mn~(2+) to Mn~(3+). Process C: Generation of bromide and reduction of Mn~(3+).
The time of initiation (τ_i) can be divided into two parts τ_(i1) and τ_(i2), is determined by the process A (i.e the rate of bromide consumption), as the consumption of BrO~-_3 and H_2SO_4 is increased, the rate of Br~- consumption is increased, τ_(i1) therefore, must be decreased. τ_(i2) is determined by process A, B and C. It is decreased by the acceleration of process B, C and increased by increased the rate of bromide consumption. As a result, at higher concentrations of H_2SO_4 and BrO~-_3, τ_(i2) will be increased, τ_(i2) will change in opposite direction by increase of the concentration of Mn~(2+). High [Br~-] can increase process C, then τ_(i2) decreases.
Based on the experiments, the following relationship can be obtained:
1/τ_(i1)=k_1[BrO~-_3]^(0.92)_0[H_2SO_4]~(1.63)_0[Br~-]~(-0.56)_0[IA]~(0.25)_0 exp(-E_(i1)/RT)
1/τ_(i2)=k_2[BrO~-_3]~(-0.53)_0[H_2SO_4]~(-0.50)_0[Br~-]~(3.28)_0[IA]~(0.25)_0[Mn~(2+)]~(0.78)_0 exp(-E_(i2)/RT)
E_(i1)=66.9 kJ.mol~(-1) E_(i2)=112 kJ.mol~(-1)
The oscillation period is mainly effected by H_2SO_4 and BrO~-_3. The polt of lnτ_p vs ln[H_2SO_4] is not a straight line.
1/τ_p=κ[BrO~-_3]~(0.44)f_(H_2SO_4)exp(-E_p/RT) E_p=100 kJ.mol~(-1)
It was also found that τ_(i2) and τ_p decrease with the increasing of concentration of glucose.
The electroreduction of chlorate was studied with Mo disk-Pt ring electrode. Two reduction intermediates, ClO_2 and Cl(or Cl_2), have been detected. Some kinetic parameters of the electroreduction of chlorate and reaction orders of reactants were obtained with rotating electrode. According to experimental and calculated results, a mechanism of the electroreduction of chlorate is postulated.
A technique was developed for simultaneous ESR-electrochemical measurements of surface radicals on porous electrodes. The ESR-electroehemical cell consists of a Teflon bonded carbon electrode(WE) and a porous Ag electrode(CE)packed parallelly with a separator in between. A grain of Ag/Ag_2O is placed in the separator,serving as the reference electrode. The electrolyte contained in the cell is no more than 4μl, confining the dielectrical loss to an tolerable level. Using the cell we have been able to obtain the ESR signals of surface radicals generated by electroreduction for a quinone-modified RB carbon electrode. To our best knowledge, this is the first report on ESR spectra with hfs for species adsorbed on electrode surfaces. It is deduced from the ESR data that on the electrode surface there are several absorbed radicals with different electrochemical behaviors. In the potantial range studied, there seem to be four types of surface quinoid compounds which can be reduced according to a radical mechanism. Two of them exhibiting hfs are probably surface species linked to the carbon surface by a singl bond, (possibly through a surface group) while the other two which give the anisotropic spectra are assumed to be multi-site absorbed.
The surface structure and the valence change on sulfided MoO_3/γ-Al_2O_3 catalyst samples were investigated at different sulfidation conditions and before or after methanation reaction using XPS, ESR and TEM methods. The main results were obtained as following. The most of Mo~(+6) were easily reduced to Mo~(+4) during the samples were sulfided. Very small amount of Mo~(+5) existed and decreased when the sulfidation time was increased. More amount of Mo~(+5) was only detected by XPS on the samples of lower Mo content at lower reduction temperature and at shorter sulfidation time. The major valency of sulfur was -2 during the sulfidation proceeded. A small amount of high valence sulfur was detected and vanished during prolongation of sulfidation time. No change of the valence of Mo or S was observed after reaction for 8 hrs. It was demonstrated by TEM photogragh and diffraction pattern that MoS_2 microcrystal grew up remarkably on the sample surface after methanation reaction.
The relations between preoscillatory period τ as well as oscillating period T_2 and each reactant initial concentration have been studied. The formula at 302K are:
τ=22.8 c~(-2.23)_(H_2SO_4) c~(-2.17)_(KBrO_3) c~(0.795)_(GA) (mol.dm~(-3))~(4.25)·s
T_2=0.84 c~(-2.28)_(H_2SO-4)c~(-1.97)_(KBrO_3) exp{(0.000147(mol.dm~(-3))~2/c~2_(GA)}(mol.dm~(-3))~(4.25)·s
The major conclusions are:
(1): τ and T_2 decrease while increasing concentrations of KBrO_3 and H_2SO_4, which is similiar to classical BZ systems(1).
(2):τ and T_2 increase with increasing the concentration of GA (Gallic Acid), which is contrary to the classical BZ systems. This implies that organic subtrate GA plays special rule in the oscillation of GA-KBrO_3-H_2SO_4 system.
With the method of CV(Cyclic Voltammgrams) the effects of GA in this system have been studied. It has been found that when preoscillatory period ends GA is almost exhausted. In other word, It is impossible to hold oscillation of this system with GA subtrate. In fact, GA subtrate only supplies the substances that hold oscillation of this system. Therefore, The explanation of OKN mechanism~([4]) to this system is not available.
It has been studied that the effects of Fe(Phen)~(2+)_3 on the oscillation of GA-KBrO_3-H_2SO_4 system. It has been found that the oscillating behavior of Br~- ion will change with the concentration of Fe(Phen)~(2+)_3, ie, at low concentration of Fe(Phen)~(2+)_3 the behavior of Br~- ion is similiar to that of GA-KBrO-H_2SO_4 system, at high concentration of Fe(Phen)~(2+)_3 the behavior of Br~- ion is contrary to that GA-KBrO_3-H_2SO_4 system. The significant differenc es are that before the oscillating pulse of Br~- ion during each oscillating period the former is gradual increase of Br~- ion concentration and the latter is gradual decrease of Br~- ion concentration. The kind of phenomenon in chemical oscillations is first discovered. This implies that the oscillation of GA-KBrO_3-H_2SO_4-Fe(phen)~(2+)_3 system cannot be explained with OKN mechanism. The oscillation is phenomenally couple of two different oscillations.
Two different mechanisms have been put experimently forward for the photoreaction, in which HNO and CH_2O under both irradiation conditions at λ_(EXC)≥645 nm or λ_(EXC)=345 nm can produce cis and trans nitrosomethanol. In present paper, we located the S_0, S_1 and T_1 transition state and traced the IRC's of the reaction based on the ab initio method with STO-3G basis set. Using the GUGA CI method, we also calculated reactive and exciting energies of the reaction system. Our theoretical results support one of the two possible mechanisms suggested by experimentalists. We showed that whether the reactants are irradiated by light of λ≥645 nm or by light of λ=345 nm, in the first step of the reaction, the product formed will be trans nitrosomethanol.
The apparent thermodynamic functions of the protonation and coordination of N,N′-(para-substituted phenol) ethylenediamine with Cu (Ⅱ) has been determined at 25.0±0.1 ℃ and I=0.1 mol.dm~(-3) (NaClO_4) in 90% (V/V) ethanol by the constant temperature environment-continuous titration calorimeter which had been constructed in our laboratory.
It has been found that the heat of protonation (H_(L1)) is linearly correlated with the Hammett constants and the formation of H~+ bridge occurs in ~H+ -N, N′-(p-RPh)_2en (1:1) systems.
Electrodes coated with Nafion polymer films in which the cationic copper-bipyridyl complex(Cu(bpy)_2~(2+)) has been incorporated have been investigated by using XPS,ESR and cyclic voltammetric means. It is revealed that there exist considerably strong interactions between the incorporated species and the polymers, sulfonic sites,and that (at least) two kinds of environment are involved in the films. Much larger cyclic voltammetric response of the incorporated species (Cu(Ⅱ)←→Cu(Ⅰ)) is observed when a small amount of acid and/or, particularly, organic reagent which is electrochemically inactivei is added to the aqueous solution. The experimenatal results are explained by taking the different regions of Nafion into account. It is also preliminarily demon strated from cyclic voltammetry that the incorporated complexes in the polymer films exhibit electrocatalytic activity toward the reduction of dioxygen dissolved in the aqueous electrolyte.
The localized molecular orbitals(LMO) of selected about 20 organic small molecules conerning H,C,N and O atoms and triple bonds are studied by use of STO-3G ab initio and Foster-Boys localized program. The LMO energies and the interactions between LMOs are calculated. The photoelectron spectra of the molecules involving triple bonds are analyzed using LMO model and the results are in quite od agreement with experimental values obtained from photoelectron spectra.
The fluorescence spectra and lifetimes of the ternary due mixture C440/C540/Saf. -T were studies. Experimental results indicated that there are efficient energy transfer among these three components of the dye system. Consequently this system may he expected to be a potemtial eandidate of laser dye giving out output in three different wavelength regions. From. the relation of donor fluorescence lifetime as a function of aceeptor concentration and the relation of accepter fluorescence intensity as a funotion of acceptor concentration and the relation of accepter fluorescence intensity as a function of donor concentration, the main mechanism responsible for energy transfer in this system is suggested.
The existence of the surface and the lattice oxygen of V_2O_5 has been investigated by the temperature programmed desorption-mass spectrography (TPD-MS) technique. Four peaks were recorded for a TPD-MS run. They are tentatively assigned to be the adsorbed oxygen (Ⅰ, Ⅱ), the surface lattice oxygen (Ⅲ), and the lattice oxygen in the bulk. The ratio of the oxygen of peak Ⅳ to all of the oxygen in V_2O_5 (see Table 1 ) is 0.20 which implies that the lattice oxygen in the bulk of V_2O_5 desorbes according to the reaction:
V_2O_5→V_2O_4+1/2O_2
Its activation energy of desorption E_d is 217 kJ.mol~(-1) with a pre-exponential factor A=2.3×10~8 s~(-1) (2nd order). On the contrary, the E_d and A for peak III are 386 kJ.mol~(-1) and 1.4×10~(23) s~(-1) (1st order), respectively.
The difference between our TPD result and that of the references [4,3] has been discussed.
The H_2 reduction behaviours of MoO_3/Al_2O_3, MoO_3/TiO_2 and NiO-MoO_3/TiO_2 samples prepared by impregnation method were studied at various temperatures for different times by XPS technique. The recored XPS spectra of Mo3d from those samples were treated by computer curve fittingprogram to measure the distribution of various molybdenum oxide species with different valence states. The results of computer fitting shows that there areMo(Ⅵ), Mo(Ⅴ)and Mo(Ⅳ) on the all of reduced samples. However, after H_2 reductonin same way, the percentage of low valence species Mo(V) and Mo(IV) on the MoO_3/TiO_2 is much higher than on the MoO_3/Al_2O3 (Fig.2). For example, after H_2 treatment at 500 ℃ for 2 hrs., Mo(IV) species on the surface of MoO_3/TiO_2 sample is about 60% and it is three times higher than what is found on the MoO_3/Al_2O_3 sample. In addition, the reduction of molybdena on TiO_2 support is much easier and faster than on Al_2O_3 support (Fig.3). Addition of NiO further promotes the reduction of molybdena to cause the strting reduction temperature producing Mo(IV) and Mo(V) to be decreased about 100 ℃. and 80% of molyb dena on NiO-MoO_3/TiO_2 support could be reduced to Mo(IV) (Fig.2). A detail discussion about the interaction between molybdena and carries was presented. It was suggested that TiO_2 is certainly involved in the reduction and oxidation process of molybdenum oxide species on the surface of it.
The kinetic parameters of grain boundary and precipitate interface in 18 Ni maraging steel were studied by gas chromatograph as hydrogen detctor. The evolution rate peaks of grain boundary and precipitate interface appeared at 378 K and 405 K with 3.00 K min~(-1) heating rate and 0.55mm specimen thickness. The trapactivation energies needed to escape from these sites were obtained from the relationship between peak temperature and heating rate to be 14.2 kJ mol~(-1) and 23.1 kJ mo1~(-1), respectively. The rate constants of hydrogen evolution from these were 3.39 exp (-14.2/RT) min~(-1) and 26.34 exp(-23.1/RT) min~(-1), respectively.
The single crystal of the title complex was studied by ESR at X-band, room temperature. Data were collected in three ortho nal planes based on the crystal shape. The Hamiltonian parameters were calculated using the least-square fitting program developed recently for the non-coincident system of g and A tensors. It was found that the physically unequivalent copper(Ⅱ) in the unit cell had the main values of g and A: g_(z′)=2.351, g_(x′)=2.083, g_(y′)=2.078, A_(z″)=160×10~(-4) cm~(-1), A_(x″)=22×10~(-4) cm~(-1), A_y″)=16×10^(-4) cm^(-1).
The molecular orbital coefficients of Kramers doublet had been calculated, with results a=0.905, b=0.256, c=0.173, d=e=0.0317 corresponding to the coefficients of atomic orbitals d_(x~2-y~2), d_(z~2), d_(xy), d_(xz) and d_(yz) respectively.
