2000 Vol. 13, No. 1

Article
Study on the state distribution of nascent product NH2(2A1)in the reaction of Ar(3P0,2)+NH3 under beam condition has been reported firstly herein.The emission spectra of NH2(-) were assigned in detail.Most of the emission bands are attributed to(0,ν2',0)-(0,0,0)transition with ν2' 5,k'a≤6,J'≤10.Rotational temperature around b/c axis of level(0,2,0,K'a=1)is 1050K,which is higher than that of the parent NH3.It should be attributed to the recoil effect of collisive partner when Ar separates from NH3.
CF radicals were generated by using a dc discharge in the mixture of Ar/CF4,Ar/CF2Cl2,and Ar/CF3COOH.The rotationally resolved(2+1)resonance-enhanced multiphoton ionization(REMPI)spectra of CF radical have been investigated in the wavelength range 260~360nm.The analysis shows that the observed spectra can be assigned as the two-photon resonance excitation 3pπD2Πr(ν'=2~6,r=3/2,1/2)←←X2Πr(ν"=0,r=3/2,1/2).The related rotational constants and the spin-orbit splitting values of CF 3p Rydberg state have been derived.
The multiphoton ionization of the hydrogen-bonded clusters C4H5N-(H2O)n was studied using a time-of-flight mass spectrometer at 355nm and 532nm laser wavelengths.At both wavelengths,a series of C4H5N-(H2O)n+and the protonated products C4H5N-(H2O)nH+ were obtained.The two-photon resonance ionization processes at 355nm make the ion intensities of pyrrole and the clusters obviously more abundant than at 532nm.Ab initio calculations show that in the protonated products,the proton prefers to link with α-C of pyrrole rather than with the N atom.The production of the protonated products needs an intracluster proton transfer reaction.The protonated products obtained at 532nm are suggested to arise from an intracluster penning ionization or a charge transfer process.The abnormally higher intensities of photofragments C4H4N-(H2O)n+(n≥1) than C4H4N+ are attributed to the stabilization effects of the cluster formation on the dissociation products C4H4N+ of the pyrrole molecule.
The abstract reaction of CH3SiH3 with H has been studied by using the“direct dynamics”method of variational transition-state theory,which is based on the information on geometries,frequencies and energies calculated by ab initio along the minimum energy path.The rate constants and transmission coefficients were calculated for the temperature range 298~1700K.The result indicates that the variational effect on this reaction is great and the tunneling effect is very obvious at room temperature.The rate constants calculated match well with the experimental value.
Ga2O3 thin films have been fabricated using 355nm pulsed laser deposition.XRD and AFM measurements showed that the films mainly consist of nanosized polycrystalline β-monoclinic Ga2O3.Photoluminescence(PL)spectra of the thin films deposited at various oxygen pressure were measured.With the increase of oxygen pressure,the PL intensity increased along with the wavelength red-shifts of the emission band,which may be due to the increase of the grain size.CeO2 dopant can enhance the PL intensity and influence the PL spectrum obviously.Additionally,the time-resolved emission spectrometry was used to characterize the ablated species generated from the laser ablation of Ga2O3.Gallium oxide species in the plume increased with increasing the oxygen pressure and the laser fluence.
The collision reaction that Kr(1Sg)+HF(X1Σ+;ν=1,2,3;J=4)→Kr(1Sg)+HF(X1Σ+;ν',J')has been studied using Monte-Carlo trajectory method,and it has been found that Kr atoms have in fluence on the fundamental and overtone vibrational frequency for HF(X1Σ+).The studying results show that,when the initial relative translational energy Et≤251.0kJ/mol,Kr atoms can reduce the particle number reversion of the fundamental vibrational frequency,and increase it of the overtone vibrational frequency,particularly in the energy level ν'=2,and Kr atoms are more strong on relaxing the higher rotational states(J'≥4).Thus,for hydrogen fluoride(HF)overtone frequency laser Kr atoms can obviously increase the strength of light and improve the transmission property in the air.
The Si,Al ordering in zeolite A(formula Na96Al96Si96O384)has been studied theoretically using steric energy minimization by simulated annealing.The consistent molecular mechanics force field is used.Calculations are performed on four kind of Si,Al distributions:i)the 4:0 ordered structure,in which Lowenstein's rule is obeyed and no Al-O-Al bridges occur,ii)and iii)two hypothetical structures having 3:1 framework ordering,i.e.,each silicon is connected by oxygen to three aluminum atoms and one silicon atom,iv)a structure with random Si,Al distribution and three kind of cation occupations:i)The experimental Na+ occupation;i.e.,Na+ occupy sites I ,II and III with 64,24 and 8 per unit cell,respectively;ii)and iii)Na+ occupy sites I,II and III randomly.The steric energy,the heat of formation and unit cell parameter of each refined structure are obtained.An energetic preference for the Lowensteinian Si,Al distribution and the experimental Na+ occupation are found.
Ab initio molecular orbital method is used to theoretically investigate the interactions of water with the different sites of Al(111)surface.Al10 cluster is used to simulate the srface,the adsorption energies and geometries are calculated at different basis site level.The results show that water prefers to adsorb on the top site of the Al(111)surface and it has two stable orientations.When water molecule is farther from the surface,it is adsorbed with hydrogen atom near the surface,then reaches the optimum adsorption site when oxygen atom is near the surface.Giving no consideration of the d orbitals of oxygen atom,the optimum structure is the water plane normal to the surface.When the d orbitals are taken into account,the calculated structure of adsorbed monomer with an inclined molecular axis about 40o is in agreement with the experimental results,so the critical effect of dorbitals of the oxygen atom on the structure of adsorbed water monomer is recognized.Also the effect of charge on the adsorption system is discussed.The results indicate that on the surface with positive charges,oxygen atom is near the surface,Al-O equilibrium distance decreases;on the surface with the negative charge,the results are opposite,H near the surface is the stable structure.
B3LYP/6-31G(d)-DFT(Density Functional Theory)method has been employed to study benzofuroxan,o-dinitrosobenzene and the isomerization between them.The calculated results with B3LYP/6-31G(d)-DFT show:(1)the molecular total energy of benzofuroxan is lower than that of o-dinitrosobenzene;(2)the activation energy(Ea+=51.0kJ/mol)of forward reaction that benzofuroxan isomerises into o-dinitrosobenzene,is in agreement with the experimental(58.6kJ/mol)provided by reference,and the activation energy(Ea-=4.6kJ/mol)of back-ward reaction is very small.It is concluded thereby that benzofuroxan is more stable than o-dinitrosobenzene.In addition,the corresponding ab initio calculations at the level of HF/3-21G,HF/6-31G(d)and MP2/6-31G(d)//6-31G(d) were completed,and it was found that the calculated results by B3LYP-DFT method are superior to those from ab initio calculation.The calculations of harmonic vibrational frequencies with B3LYP/6-31G(d)theoretically supported that o-dinitrosobenzene is the intermediate of “self-self”tautomeric rearrangement of benzofuroxan.
The reaction of three monocycle-β-lactam and OH- have been studied by the method of AM1 in MOPAC program.The available mechanism has been obtained.Calculation results show that there is charge transfer in the active four-numbered cycle during reaction,both the negative charge of N atom and the positive charge of C atom on acyl-amine bond increase,it is useful to nuclephilic reaction.By calculating active energy,it has been learned that the active energy of three compounds is small,which is indicated that it is profitable for the reaction in base condition.At the same time,the certain relationship between the active energy and the activity of compoundshas been shown:the smaller the active energy,the stronger the organism activity of compounds.
The average energy level(i)of valence electron is defined as i=(ni-1)(ni+ΣEij)0.5/(1+mi).The new connection index 0Qand 1Q which are set up by i are defined as 0Q=Σ(i)-0.5 and 1Q=Σ(ij)-0.5.The correlation coeficients of 0Q and ΔE,0Q2 and ΔE,1Q0.5 and U,pKa and 0Q,1Qare 0.9734,0.9769,0.9906,0.9945 respectively.Their correlativities are even more ideal than those of the literature methods.mQ is a new molecular topogical index which have good structurese lectivity and highly property corrlativity.
With the graphic method and no linear programming,twelve structural-type properties and condensed-type properties of homologous straight-chain alkanes,such as the highest bonded molecualr orbital energy,the lowest bonded molecular orbital energy,ionization energy,half-wave potential of oxidation,normal boiling point,normal melting point,critical pressure,critical temperature,density,refractance,surface tension and vicosity,have been developed.The results show that strutural-type properties and condensed-type properties of straight-chain alkanes generally obey the homologous logarithm regularities,and various structural-type properties and condensed-type properties are very well correlated with logarithmic function,and correlation coefficients all more than 0.99.Using homologous logarithm regularities,various properties of homologous straight-chain alkanes are predicted,and the findings indicate that most of the predicted values correspond very much to the values in literature except that deviations for minority of beginning compounds are not ideal,and experimental points almost over-lap on the curves drawn by the logarithmic functions.
Procedure for preparing Mo2C thin film by metalorganic chemical deposition(MOCVD)and experimental data on interface roughness are provided,and the rule for distribution of interface height and height difference is given on basis of measured data.Simulation of 2+1 Dimension interface for Mo2C thin film is carried out through generation of DT2 model.The results show that the distribution of height and height difference is agreement with computer simulated one.
Nano-crystal palladium was prepared through the chemical liquid phase synthesis method.Thermal stability study shows that the average diameter of n-Pd against the annealing temperature fits Arrhenius relation(in the temperature range of 773~523K).The average diameter against the annealing time fits the empirical formula =ktn.The thermal stability temperature is below 250℃。By calculating,we get the apparent growth activation energy about 0.15eV,which is far smaller than ordinary nano-composite material.So,n-Pd is very easy to grow,and possesses a narrow thermal stability temperature range.
Effects of the concentration of tetraethylammonium hydroxide(TEA-OH)in gel on the structure and the thermal decomposition of as-synthesized zeolite Beta have been explored.Under synthetic conditions of this study,the optimum concentration of TEA-OH(TEA+/Al)is from 2.10 to 1.68,the relative crystallinity of synthetic β-zeolite is over 84%.The relationship between aluminium content(Al/Al+Si)or framework aluminum content(TdAl/TdAl+OhAl) in β-zeolite and TEA+/Al ratio in gel,has an optimum point.At the optimum point of TEA+/Al in gel with 1.9,Beta zeolite with a lower non-framework aluminium(OhAl) content and a higher framework Si/Al ratio can be obtained.The thermal decomposition of as-synthesized Beta zeolite is Hofmann degradation,and the weight-loss by TGA,the total endotherm by DSC are closely related to the TEA content in as-synthesized Beta zeolite.
Polyacrylamide(PAM)-MS(M=Cd,Pb,Zn)nanocomposites were prepared by a convenient in situ polymerization-hydrolysis technique(SPH).The so-called SPH technique is based on the mechanism of the simultaneous polymerization of organic monomer and formation of semiconductor nanoparticles.It was found that the semiconductor nanoparticles were well homogeneously dispersed in the polymer matrices.This SPH technique may provide a new method for fabrication of other metal sulfide-polymer hybrid nanocomposites.
The experimental results of superparamagnetic iron oxide contrast agent and electronic neutral metal complex of manganese contrast medium were observed by magnetic resonance T2 imaging and T1-weighted imaging,respectively.The data measured from the images of rat’s liver in vivo show that the two types of contrast media are able to change remarkably the T2 and T1 of tissue of rat liver,respectively.The experimental results have high value as a reference to research of MRI contrast agents and the clinic application.
Newly-synthesized polyimide(PI) LB films were deposited and used to align ferroelectric liquid crystals(FLCs).Atomic force microscope was used to investigate the morphology of PI LB films.It is found that LB films show different crystalline structure when they were treated by the different imidization temperatures.The LB films imidized at the high temperature show the orderly oriented polymer chain structure on the sustrate surfaces while the low temperature treated LB films show an irregular amphours-like aggregate structure.It demonstrates that these two types of PI LB films show different surface orderness and crystallinity.The surface-stabilized FLC cells that are aligned by the high temperature imidized PI LB films have the fast response times of 80 and 90μs to the rising and decaying stages respectively and an excellent bistability to the completeness,while the cells which are aligned by the low temperature imidized PI LB films show slower response times longer than 1ms and the incomplete memory capability.According to the AFM observations and the charge-transfer model in the interface between LB alignment films and the FLC layer,it is regarded that the LB films imidized at the high temperature can provide a higher energy barrier than that of imidized at the low temperature,which facilitates the appearance of FLC bistability.In addition,the ultra-thinness of LB films is beneficial for the neutralization and release of the surface charges brought out during the switching process,which guarantees the obtainment of excellent bistable memory capability and the realization of fast response up to micro-seconds in the surface-stabilized FLC devices.
Through removing polymer physisorbed on the glass fiber surface with solvent extraction to minimize the signal of the polymer in IR and XPS analysis,the interaction was studied by IR and XPS between maleic anhydride grafted polypropylene(MA-g-PP)and an amino silane coupling agent-γ-aminopropyltrimethoxy silane(APS).It is found that the absorption bands of polypropylene still exits in IR spectra of the glass fiber after 72h dimethyl benzene extraction and a new state of N1s at 401.9eV appears in the XPS,which shows that the MA-g-PP and APS have reacted chemically and the reaction product with amido is formed.Although open chain APS and cyclic APS with an internal hydrogen bond coexist on the APS treated glass fiber surface,it is discovered that APS which reacts chemically with MA-g-PP is mainly open chain APS by the quantitative analysis of XPS for N1s in different chemical state.
A study was undertaken to investigate the desorption of CO2 in the six polymers,namely,LDPE,PP,PA6,EVA,PS and PU.The six polymers were treated in supercritical CO2.The temperature of supercritical CO2 was 40℃,pressure was from 8.0 to 14.0MPa.The weight change of polymers after treatment was fitted with two functions.One function was Y=Y0+Aexp{-(t-t0)/τ},the other was Y=Y0+A(t-t0)1/2.The result indicated that the weight change of polymers after treatment in mass with time showed a dependence on the logarithm of time.The desorption equation of CO2 in polymers was given in accordance with Fickian diffusion law.The diffusion coefficient of CO2 was calculated with the desorption equation.The result suggested that the diffusion coefficient of CO2 was about 10-7cm2/s and it depended on the amount of CO2 in polymer,temperature and the treated pressure.
This paper measured the π-Aisotherms of the monomer and polymerized 10,12-pentacosadiynoic acid(PDA).If defining A0 as the surface pressure onset(the area at which an appreciable rise in surface pressure was observed),the A0 are 0.35 and 0.48nm2/mol,the collapse pressure are 51 and 38mN/m and the molecule area at collapse point are 0.2 and 0.28nm2/mol for PDA monomer and polymer respectively.The chain segment of PDA polymer occupied more area than the corresponding monomer.So expansion could be expected in the polymerization reaction.The PDA molecule area changes during polymerization at the surface pressure of 10mN/m was recorded.It was obvious an expansion process.The UV-visible absorption and emission spectroscopy of the polymerized products were measured.The 500 and 550nm absorption peak indicated that the polymerization was really occurred in the monolayer state.The acceleration effect of visible-light on the monolayer UV-polymerization was investigated by periodically switch on and off the visible-light under constant UV-irradiation.The barrier speed at the visible-irradiation periods was larger than that at the no-visible-irradiation periods.This indicated that the visible-light can truly accelerate the UV-polymerization of PDA monolayer.Because the visible-light itself can not initiate the polymerization without UV-irradiation,it can be concluded that the visible-light can only accelerated the chain propagation process,thus can produce larger molecule weight polymer.The acceleration effect was explained with the polymerization mechanism and the electronic state of the polymerization intermediates.
Micelles of Pluronic block copolymers have recently displayed a potential application as drug microcarriers.In the application,one of the key problems is effective solubilization of hydrophobic drugs in the micelles.However,solubilization regularities of hydrophobic materials in Pluronic micelles have not been fully studied.In this paper,the solubilization of pyrene(Py)in the aqueous micellar solutions of Pluronic block copolymers has been investigated by steady-state fluorescent spectra.The results showed that the PPO content in Pluronic molecule is a key factor to determine Py amount adsorbed in the micelles.The greater is the PPO content,the much favorably solubilizate Py in the micelles.In the molecules of Pluronic copolymers studied in this paper,PPO content orders as F108(2920)>P85(2300)>F68(1680)and thus the partition coefficients(KV)of Py between the micelles and water are 8.3×104(F108,35℃),5.7×104(P85,35℃)and 2.2×103(F68,40℃),respectively.Addition of KCl leads to formation of the larger micelle with less hydrated shell.This means formation of a larger micellar core available to accommodating hydrophobic Py molecules,which is in agreement with the experimental results that showed an enhancement in Py solubilization as addition of KCl.
The electronic structures of Dawson anion(S2Mo18O62)4- have been calculated by the discrete variational method coupled with the first principal density functional theory(DFT-DVM).And the comparison with Keggin anion(SMo12O40)2- has been made.The results show that the electrons delocalize around the all anion.But the difference of the electronic distributi on of polar and equator sites exists.The bonds which formed by terminal oxygen and Mo are stronger and the bonds formed by centre oxygen and Mo are weakest.The active centers of chemical actions are Moe(which is at the equator sites),Opt,Opea(at polar sites)Oet,Oeb,,,(at equator sites).Compared with (SMo12O40)2-,the stability and oxidation ability of (S2Mo18O62)4- are weaker.To the two anions,the Molybdenum atoms pay an important role in their redox effects.