2004 Vol. 17, No. 1

Letter
Up to Kr17 + multicharged krypton ions have been observed in time-of-flight mass spectrum by a 25 ns Nd-YAG 1. 064 μm laser at laser intensity about 1012 W/ cm2 . Experimental results indicate that the multicharged ions appear only when the laser interacts with the middle part of the pulsed beam,and the intensities of the multicharged ions increase dramatically by increasing the backing pressure of Kr gas,which indicates that the clusters in the beam is essential to the production of multicharged ions. From the experimental results,it is concluded that the cluster is ionized via multiphoton ionization and forms a nanoplasma ball,which can absorb the laser resonantly to further ionize the single charge ion to the high charge state.
Article
Under single-collision conditions,a beam of metastable molecules CO( a,v')generated by DC discharge was allowed to collide with a beam of NO(X)at a fixed angle of 90o . The collision-induced emission from the interaction region was collected at right angles to the beam plane by a lens set and dispersed by a 1 m monochromator where a cooled photomultiplier tube was mounted on the exit slit. The signal from the PMT was transmitted via a discriminator,a photon counter and a boxcar integrator into a computer for storing and processing. Two broadband emissions were observed around the wavelengths of 780 and 860 nm,which can be assigned to NO(b-a) Ogawa bands Δv = + 4 and + 3 sequences,respectively,and referred to the spectroscopic data given by Huber. At the collision energy of 0. 05 eV in the present experimental conditions,the electronic energy of CO( a,v' = 0)(6. 01 eV)was not enough to excite NO(X)to NO(b,v' = 4,5)(ΔE > 6. 11 eV). So,what was in act in the energy transfer was the vibrational excitation of CO(a,v' > 0),and the higher the vibrational excitation of CO(a,v') was,the stronger the emission intensity of NO( b-a)could be obtained. It is thought that electron exchange between CO(a)and NO(X)may be operative through the formation of a complex OCNO. The newly discovered formation of NO( b)channel could be well explained considering the energy conservation,spin conservation and electron exchange mechanism.
The fluorine atom reaction with trans-1,3-butadiene has been investigated by using the crossed molecular beam method. Signals at mass 72,46 and 33 have been observed. A single reaction channel C4H5F + H is observed for this reaction channel. Product angular distributions and velocity distributions are determined. The experimental results indicate that the channel mainly proceeds via a long-lived complex at a collisional energy of 23. 8 kJ / mol. The collision complex is likely formed with the F atom attacking the delocalized electrons in the direction perpendicular to the molecular plane of trans-1,3-butadiene molecule.
The stable structures and vibrational spectra of protonated acetone molecule clusters with different sizes (CH3COCH3)nH +(n=1-7)are calculated at the 6-31G(d)level by means of density functional theory (B3LYP)quantum chemical calculations. The corresponding energies are analyzed at the level B3LYP/6-311+G(3df,2p)in order to obtain more accurate results. The proton affinity of neutral cyclic acetone molecule clusters increases with the increasing of cluster size. The calculated results show that the protonated acetone clusters have certain growth regularity with forming a solvation shell at the beginning and then new added acetone molecule attacking different active sites including the middle carbon atoms and the different methyl in solvation shell. The IR spectra of the protonated clusters are more complicate than that of neutral ones. The strongest peaks result from the movement of the proton between the two oxygen atoms in solvant shell apart from the case of n=1. Carbonyl stretching vibraional peaks split into the more and more and in general the corresponding intensities are weakened due to the protonation with the increasing of cluster size.
Based on the atomic and molecular reaction statics,the ground electronic states i. e. BBr(X1Σ +),BBr+(X2Σ+)and BBr2+(X1Σ+)and the corresponding reasonable dissociative limits for these molecule and ions have been derived. Using the density functional method(B3LYP)and cc-pVDZ basis sets,the molecular equilibrium geometry and dissociation energy for BBr+(X2Σ+)and BBr2+(X1Σ+)have been calculated. The analytical potential energy functions of BBr and its ions BBr + and BBr2 + are correctly determined. The force fields and spectroscopic have been worked out from their analytical potential energy functions parameters of BBr+(X2Σ +)and BBr2+(X1Σ+). The calculated results for Re,De,f2,f3,f4,Be,αe,ωe and ωexe are 0. 1766 nm,3. 531 eV,4. 88 aJ/cm2,-27.29 aJ/cm3,111. 03 aJ/cm4,0. 5677,0. 00477,932. 5 and 6. 057 cm-1 respectively for BBr+ and 0. 1726 nm,2. 452 eV,23. 711 aJ/cm2, -175. 61 aJ/cm3,611. 96 aJ/cm4,0. 5945,0. 001774,261. 079 and 1446. 2 cm-1 respectively for BBr+2,which are in agreement with experimental or calculated values in references. The vertical ionization potentials of BBr are I+=9. 583675 eV and I++=29. 34234 eV. It is indicated from calculation that there are the minimum points in the potential energy curves of BBr+ and BBr2+,so it can be decided that BBr,BBr+ and BBr2+ can be stable.
As theoretical approach for synthesized molecular conductor(PyH)[Ni(dmit)2]2,two-dimensional energy bands have been calculated by using EHMO tight binding method. Intermolecular HOMO-HOMO overlap integrals of various[Ni (dmit)2]-0.5 ?[Ni(dmit)2]-0.5 pairs in the two-dimensional conductive network have also been calculated. The calculated energy gap 0.17 eV is in accord with the measured conducting activation energy 0.15 eV,indicating that(PyH)[Ni(dmit)2]2 is a semiconductor with the narrow energy gap. Based on energy band calculation,the structure-properties correlations have been discussed. Among various structural factors,the uniformity and the compactibility of the array of the[Ni(dmit)2]-0.5 play a crucial part in influencing the conductivity of the(PyH)[Ni(dmit)2]2 crystal.
Binary components Ornstein-Zernike integral equation with the concentration of large particle component being set to zero was employed to study the depletion potential behavior between two large neutral colloid particles (modeled as hard spheres)immersed in a sea of small neutral solvent particles. The prediction for the depletion potential behavior compared well with simulation data and experimental data available in the literature. It is found that the Hansen-Verlet one phase criterion,based on the effective one component system with the present depletion potential,for the freezing transition is completely not suitable for the real binary components system. It is disclosed that the unsuitability is due to the volume term of the solid phase and liquid phase which can not be treated selfconsistently in the Hansen-Verlet one phase criterion.
Energetic materials are aggregative and mixed systems. The intermolecular interactions play significantroles in the physical,chemical and explosive property. The study on intermolecular interactions of energetic materials has attracted wide attention. The organic azides are an important category of energetic materials and widely used in many fields. Ethyl azide is the simple model having the explosive property for the organic azides energetic compound. Ethyl azide monomer(Ⅰ)and all its possible stable clusters(Ⅱ,Ⅲ and Ⅳ)are fully optimized by ab initio method at the HF/6-311++G** level. Vibrational frequencies calculated to ascertain each structure are characterized to be the stable structure(no imaginary frequencies). The proportions of correlated interaction energies to their total interaction energies ΔE(MP2)are 65.14%,63.76% and 65.62% for Ⅱ,Ⅲ and Ⅳ respectively. In addition,the basis set superposition error(BSSE)correction energies are 7.82,7.61 and 4.40 kJ/mol for Ⅱ,Ⅲ and Ⅳ respectively. The zero point energy (ZPE) corrections for the interaction energies are much less than those of MP2 electron correlation and BSSE correction energies. After MP2 electron correlation correction,BSSE and ZPE correction,the greatest corrected intermolecular interaction of the dimers is -10.45 kJ/mol. The charge redistribution mainly occurs on the adjacent N?H atoms between submolecules. The charge transfer between two subsystems is very small. Natural bond orbital(NBO)analysis is performed to reveal the origin of the interaction. Based on the statistical thermodynamic method,the standard thermodynamic functions,heat capacities(C0p),entropies(S0m)and enthalpies(H0m)and the changes of thermodynamic properties from the monomer to dimer with the temperatures ranging from 200. 00 K to 800. 00 K have been obtained.
Recently,a series of sensing films based upon the supra-molecular behavior of aromatic compounds immobilized on substrate surfaces and its dependence to the composition of the medium have been successfully prepared. It is found that the properties and performances of the films depend upon various factors,including the nature of the sensing element,the way of immobilization,the nature of the substrate,and the density of the sensing element immobilized etc. To accelerate and deepen the studies,it was decided to carry out the theoretical simulation of the sensing films based upon the proposed principle. The fluorescence behavior of a functional plate,of which the surface is functionalized by single layer immobilization of aromatic compounds(sensing elements),is simulated by Monte Carlo simulation method. The effects of the immobilization density of a sensing element,the excitation efficiency,and the association efficiency,P,which is a characteristic parameter of an aromatic compound,between the molecules of the sensing element on the ratio of the excimer emission to the monomer emission of the plate have been systematically examined. But the effects of the length and flexibility of a spacer are neglected,because in this simulation aromatic compounds are immobilized on a plate by the short stiff spacer. It is demonstrated that,for a functionalized plate of a short stiff spacer in a polar solvent( in this case,the association tendency is strong,and P is close to 1),aromatic compounds of middle excitation efficiency might be suitable as sensing elements. In addition,the immobilization density of the sensing element should be controlled. A recommended value is about 50%.
To enhance the binding ability of β-cyclodextrin with naphthalene derivatives,a hydrophobic group to the rim of β-cyclodextrin was added and the new β-cyclodextrin compound—mono-6-p-nitrobenzoyl-β-cyclodextrin was synthesized. Its binding ability for 1: 1 inclusion complexation with 1-naphthoic acid was evaluated in the KCl/HCl buffer solution(pH=1.5,0.1 mol/dm3)at 15℃ by the spectrofluormetric titration. The results obtained indicated that mono-6-p-nitrobenzoyl-β-cyclodextrin could strongly include 1-naphthoic acid in aqueous solution;the modification dramatically enhanced the original binding ability of native β-cyclodextrin by a factor 9. The binding constants of mono-6-p-nitrobenzoyl-β-cyclodextrin and other naphthalenes such as 1-methoxynaphthalene,2-methoxynaphthalene,1-N,N-dimethylaminonaphthalene and 1-N,N-dimethylaminonaphthalene were obtained from the time-resolved fluorescence. The high binging ability of naphthalenes with NBCD make it is possible to assemble stable host-guest complexes.
In order to discuss the free radicals formation mechanism of Hypocrellin A(HA)with amino derivatives,the electron-spin resonance( ESR) spectroscopy was adopted to study the photochemistry on HA with dibenzyl amine(DBA)and N-methyl benzyl amine(NMBA),respectively. When HA with DBA or NMBA in chloroform solution was illuminated with visible light,singlet oxygen,semiquinone radical and oxynitride radical were formed depending on the condition of the solvent system containing the amino-substituted and solved oxygen. The signal intensity of oxynitride radical decreased with increasing the illumination time,and the signal intensity of semiquinone radical increased with increasing the illumination time. The oxynitride radical content was in inverse ratio with the semiquinone radical generated by being irradiated. In the aerobic system of chloroform solution containing DBA/HA,smiquinone radical was the main radical irradiated. The results indicated that HA induced amino derivatives into HA semiquinone radical.
Amorphous microporous metal oxides of titanium(AMM-Ti)which can induce photocatalytic reactions under visible light irradiation was prepared by using Na2PtCl6 according to the sol-gel procedure affording high specific surface areas of 160-200 m2/g. The most active photocatalysts contained 3.0% P(t Ⅳ). According to extended X-ray absorption fine structure(EXAFS)results,isolated PtCl4 molecules were homogeneously distributed in an almost exclusively amorphous matrix of titania. During the photocatalytic degradation of 2,4-dichlorophenoxyacetic acid(2,4-D)in aqueous solution containing a suspension of AMM-Ti,it was found that 2,4-dichlorophenol was the major intermediate. The initial rate of photo-degradation was studied as a function of the initial concentration of reactants by the linearised form of the Langmuir-Hinshelwood equation,by which rate constants k and equilibrium adsorption constants K were evaluated. The postulated charge separation mechanism at Pt (Ⅳ)/ AMM-Ti and photocatalytic degradation mechanism of 2,4-D were also proposed.
As a key part of Hard Disc(HDI),the thin film of lube is possibly degraded and destroyed by the interaction between the magnetic head and disk during the hard disk working. Both TGA and FTIR are used to study lubes failure mechanism of HDI and investigate the function of X-1P as an additive in HDI lube. TGA experiment results show that the sample PFPE / X-1P / Al2O3 is much more stable than the sample PFPE / Al2O3 just as sample PFPE,and the sample PFPE / Al2O3 will degrade with high speed at enough high temperature. FTIR experiments present the results similar to that of TGA experiments. From IR sorption spectra at different heating times for the three samples,it can be found that the sample PFPE & the sample PFPE / X-1P / Al2O3 are similarly stable,but different from the sample PFPE / Al2O3 for which new CF = O absorption peak appeared after heated for 15 min and became stronger with the extending for heating time. FTIR experiment results further verifies that alumina is a catalyst for PFPE degradation reaction and X-1P can effectively passivate the catalyst and stabilize PFPE. In order to investigate X-1P's role to mechanical & tribological performances of HDI,the CSS experiment is also performed and the experiment results tell that the presence of X-1P dip-coated on the magnetic head can greatly reduce the friction between head and disk and improve CSS performance of HDI. In addition,the failure mechanism of HDI lube and X-1P's working principle as a HDI lube additive are analyzed and discussed respectively. The aluminum atom of alumina has empty orbits which can accept isolated electron pairs,and is a kind of Lewis acid with stronger electrophilic trend. Oxygen atom of PFPE has isolated electron pairs and shows nucleophilic trend. When the magnetic head contacts with the HDI lube,it is possible for alumina to induce PFPE to disproportionally degrade first from the ether bonding at enough high moment temperature. For X-1P,owing to its special molecule structure,not only has a good chemical stability but also shows stronger nucleophilic trend. When alumina contacts with the compounds of X-1P and PFPE,X-1P can be absorbed on the alumina surface prior to PFPE and keeps PFPE out of contact with alumina,and as such to protect PFPE out of degradation.
A study of oxygen permeation material Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF)is presented. The O2 -TPD,nonstoichiometry(δ),electrical conductivity(σ)and oxygen permeation were investigated. In the experiment of O2 -TPD,three oxygen-releasing peaks are observed:one peak at low temperature is attributed to the absorbed oxygen at the position of V··O,the other two peaks are related with the release of oxygen ions at two different positions in the BSCF crystal lattice. At 470℃,δ reaches minimum and σ achieves maximum:with increasing temperature,absorbed oxygen at the position of V··O is released,resulting in the first peak of O2 -TPD;the rest of absorbed oxygen entered BSCF lattice,causing the decrease of δ;the temperature dependence of the conductivity demonstrates increasing conductivity with temperatures up to a maximum at about 470℃,indicating thermally activated p-type semiconductivity,which changed to metallic conduction behavior above 470℃. Furthermore,the experiment shows that the σ maximum at the heating step is higher than that obtained at cooling step,which can be explained:when heating,some absorbed oxygen at the position of V··O enters the lattice,δ decreases and concentration of Co4+&Fe4+ increases,leading to an enhanced p-type conductivity of BSCF;on the other hand,when cooling from high temperature,absorbed oxygen at the position of V··O does not exist. In the experiment of oxygen permeation,BSCF proves to be a suitable material for oxygen-separating at above 850℃,its oxygen permeability JO2 is higher than 1 μmol/cm2 s with air as feed gas and He as sweep gas,the activation energy Ea is 63. 1 kJ/mol.
To develop gas sensing materials with high performance,high sensitivity,excellent selectivity and quick response & recovery behavior,nanocrystalline material of rare-earth composite oxide HoFeO3 with the structure of perovskite type was synthesized by sol-gel method in the system of citric acid with the Ho2O3,Fe(NO3)3·9H2O,nitric acid(1: 1 vloume fraction)as the starting materials. The structure and crystal state of the powder were determined on an X-ray diffractometer(Germany Bluker D8-Advance)with a Cu K" radiation(wavelength λ = 0. 15406 nm)operating at 20 mA and 40 kV. The shape and size were analyzed with the help of JEM-100SX Transimission electron microscopy. The results show this perovskite-type oxide is spherical with the mean grain size of 25 nm and the dispersity of it is good. The influence of temperature on the sensitivity of sensors,gas sensors's selectivity and the response and recovery characteristics are tested at the optimum working temperature 310℃. The study of sensor's gas sensing characteristic shows that the sensitivities of HoFeO3 to 0. 5! C2H5OH is 103,which is 5 times of other tested gases,such as H2S、H2、SO2、gasoline and acetone. So the sensors based on HoFeO3 show good sensitivity and selectivity to C2H5OH. The response and reversion characteristic of sensor to 0. 5! ethanol at 310℃ is good too. The response time and recovery time are 12 and 7s,respectively.
The effect of interaction(attraction effect and repulsion effect)between magnetic particles on the stability of nanometer magnetic fluids was analyzed theoretically. It was pointed that the size and concentration of magnetic particles and the coating of surfactant were important factors affecting the stability of magnetic fluids. Nanosized Fe3O4 magnetic fluids were prepared by the chemical co-precipitation method. Characterized by means of TEM,zeta potential and so on,the magnetic fluids had the mean size of 10 nm and exellent stability. The stability of magnetic fluids was researched experimentally as to the factors such as the method of adding starting materials,the speed of stirring,dispersion effect,surfactants coating occasion,coating time and adding amount,and pH. The affecting mechanism of these factors was analyzed further.
X-ray photoelectron spectroscopy(XPS)was used to study two different oxidation treatments on the GaAs(100)surface———the thermal oxidation in the air,and the ultraviolet-light oxidation in the UV-ozone. A series of properties including the oxide composition,chemical states,the surface Ga/As atomic ratio and the thickness of the oxide layer grown on GaAs surface were compared. The results indicate that the oxide composition,the surface Ga / As atomic ratio and the thickness of the oxide layer oxide on GaAs surface are different for different oxidation methods. The oxides on GaAs surface grown by thermal oxidation in the air are composed of Ga2O3,As2O5,As2O3 and elemental As;and the Ga/As atomic ratio is drifted off the stoichiometry far away. The Ga/As atomic ratio of oxide layer on GaAs surface is increases with the thickness of oxide. However,the oxides on GaAs surface grown by UV-ozone are made up of only Ga2O3 and As2O3,As2O5 and elemental As are not detected,the Ga/As atomic ratio is close to unity. The thickness of oxide layer on GaAs can be controlled by the UV exposing time. The mechanism of oxidation of GaAs is also discussed. The UV-light radiation not only causes the oxygen molecular excited forming atomic oxygen,but also induces the valence electrons of the GaAs excited from the valence band,and then the reactivity of Ga and As atom increase,and they can easily react with the excited atomic oxygen at the same reactive velocity.
The V2O5/SiO2 and V2O5-P2O5/SiO2 catalysts were prepared by the Sol-gel method. The surface composition,structure,chemisorption and reactivity of the catalysts were systematically studied by using the techniques of XRD,TPR,IR,TPD and icro-reactor. The results showed that the active component was dispersed uniformly on the surface of amorphous SiO2 . There existed Lewis base sites(V=O and V-O-V)and Lewis acid sites (Vn+)on the surface of these catalysts. An addition of PO43- could lower the activity of surface terminal oxygen of Lewis base sites V=O. Iso-butane could chemisorbed on surface terminal oxygen of Lewis base sites V=O by one or two H atoms in -CH3 to form molecular adsorption states. Reaction products of i-C4H10 on the V-P-O/SiO2 catalyst were mainly i-C4H8,MAL,MAA and COx . Conversion of i-C4H10 was 5% and selectivity of partial oxidation products is above 72% at 300℃. The addition of PO43- could improve the selectivity of partial oxidation products on the VSiO catalyst because PO43- could reduce the activity of lattice oxygen in V = O bond,and weaken the adsorption intensity of i-C4H10 .
The Ni/CeO2 -ZrO2 -Al2O3 catalyst was prepared with the hydrothermal method. The catalytic performance for the CO2 reforming of CH4 reaction with or without small amount of steam was tested and the amount of coke deposition was measured. The XAFS of Ni K-edge was attained. The results show that the formation of CeAlO3 occurs in reaction,but the coke deposition is responsible for the deactivation of the catalyst. The addition of steam into feed gas can decrease the amount of coke deposition,and promote the stability. Due to the carbon atom penetration into the Ni lattice,for the catalyst sample after reaction without the addition of steam into feed gas,the coordination number of the first Ni-Ni shell decreases sharply. For the catalyst sample after reaction with the addition of steam in feed gas,the coordination numbers of the first Ni-Ni shell decrease slightly. It is due to the addition of steam into feed gas,which can suppress the coke formation and maintain the metallic structure of active Ni metal.
It was found that IR absorption band at 1383 cm - 1 was stronger for AgBr crystal particles . This band was not observed but there was an amide I band at 1630 cm - 1 or 1640 cm - 1 for gelatin-AgBr emulsion after ensymolysis. This variation meant that gelatin was adsorbed on the AgBr crystal particles. The IR analysis was performed for gelatin with added Br- to show the possible interaction between gelatin and AgBr particles. The frequence of NH3+ absorption band for gelatins with added Br- was lower than that for gelatins without added Br-. The frequence shift of NH3+ band around 3300 cm-1 in the spectrum of gelatins indicated that gelatin could be adsorbed by AgBr with NH3+ and Br- in addition to chemical interaction between Ag+ and N atom or/and between Ag+ and S atom. Moreover,there was probably a kind of force between the hydrophobic parts of AgBr crystal surface and the hydrophobic side-chain groups of gelatin. It may be the van der Walls force. It had influence on IR spectrum of emulsion from 1000 cm-1 to 1200 cm-1 . Because there was a difference in photographic characters or crystal particle size between fish gelatin emulsion and bovine gelatin emulsion,their interactions were compared. In general,IR study suggested that gelatin was adsorbed on AgBr crystal particles . This adsorption could be caused by coulombic and van der Walls forces apart from the chemical affinity between gelatin and AgBr crystal particles.
Segmented polyesteramides have been synthesized from N,N'-bis(p-carbomethoxybenzoy)butanediamine(T4T)as crystalline segments and mixture of poly(tetramethylene oxide)with the average molecular weight 1000(PTMO1000)and 1,5-pentanediol(PDO)as soft segments. The polymerization was carried out in the melt at 250℃ for 1-2 h while vacuum was applied. The chemical composition of the copolymer was measured by H1-NMR. The melting behavior of the copolymers was studied by the differential scanning calorimeter. The dynamic mechanical properties were investigated on injection moulded bars by means of dynamic mechanical analysis. It was found that the copolymers with more than 40% molar ratio PDO showed two glass transition temperatures and two melting temperatures. The glass transition temperatures are independent of composition,and thus two fully phaseseparated amorphous phases are present. The melting temperatures change with PDO content. The amount of PDO has an effect on both TmA and TmB . TmA is attributed to the lamella consisting of extended T4T segments,while TmB results from the much thicker lamella consisting of both extended T4T and PDO segments. It is also possible that some PDO is present in the interphase as adjacent re-entry groups. So the resultant copolymer shows that a complex system,two crystalline phases,two amorphous phases and an interphase are involved in the copolymer. The undercooling for these copolymers is small,which means that these segmented copolymers crystallize fast.