2003 Vol. 16, No. 3

Letter
Femtosecond time-resolved fluorescence depletion spectroscopywas used in the study of the orientation relaxation of Rhodamine 700(LD700) and Oxazine 750(OX750) in DMSO. The anisotropy functions of the dye molecules were obtained fromthe fluorescence depletion spectra, as the polarization of probe pulse is parallel and perpendicular respectively. The results showthatthe transition dipole momentof the pump and the probe ofLD700 and OX750 are parallel. The time constants of the orientation relaxation of these dye molecules in DMSO are 1.8 and 1.9 ps for LD700 and OX750, respectively.
The ultrafine nickel particles/polyaniline nanocomposite materials were synthesized in situ polymerization by two step seriesW/O inverse microemulsion systems. As the first step, the ultrafine nickel nanoparticles whose diameter is 10~30 nm were prepared by the W/O inverse microemulsion systems and by the reduction. As the second step, the monomer aniline salt (AnH+Cl-) entered into the polar water pools where contained nickel nanoparticles and the ultrafine nickel particles/Polyaniline nanocomposite materials whose diameter is 50~100 nm had been obtained by in situ polymerization. These nanocomposite materials were measured to characterize and the micromorphology, microstructure and physical interaction of the both ultrafine nickel particles and polyanilines were studied by transmission electronmicroscopy (TEM), XRD, infraed spectrum (IR).
Article
The spectra from 2000 to 9000 cm-1which include△v=1~4(△v=m+n; mandnare vibrational quanta of excitation in two bonds) band of SiH stretching vibration were recorded by a Bruker IFS 120HR Fourier transform spectrometer. The Fourier transform intracavity laser absorption spectroscopy (FT-LCLAS) was used to record the band of △v=6 SiH stretching vibration around 12345 cm-1. The Blackman-Harris-3-Termwas adopted the apodization function in FTIR. The resolution of all the obtained spectra is 0.2 cm-1. The Si-H symmetric and asymmetric stretching vibrational modes were assigned. Assuming the SiCl2 to be a base frame for the stretching vibration of two SiH chromophores, the treatment ignored all the vibrations in the H2SiCl2 molecule except the two SiH stretching vibrations. Adopting the anharmonically coupled anharmonic oscillator local mode model (ACAO) and using the programused to optimize the spectroscopic constants of the H2X-type molecule, the Morse dissociation energy De, the Morse oscillator parameters α and the couple coefficient of the potential energy function frr′were determined by fitting the observed vibrational band centers to Hamiltonians matrix. It showed that the H2SiCl2 molecule has stronger anharmoic character and weaker inter-bond coupling. The fitting results are in good agreement with the observed levels and the standard deviation of fitting is less than 1 cm-1. Therefore, the assumption of SiCl2 being a base frame for the two SiH chromophores is proved to be a good approximation. Substituting the mass of SiCl2 base frame as the 4th variable into the program, the obtained results indicate that the effective mass of SiCl2 base frame is 75.
The detection of benzene photoions in pump-probe experiments with the femtosecond laser pulse at 400 and 266 nm has allowed to study the dynamics of the internal conversion after excitation to the electronic S2 state. For the S2 state, an extremely short lifetimeτD1=(48±1)fs has been obtained, whereas the lifetime τD2=(6.5±0.2)ps of the S1state populated by the internal conversion from the S2 state is longer than that of the S2 state. The deactivation ofthe S2 state as well as the S1state has been explained by the internal conversion to lower electronic states caused by the conical intersection of the corresponding potential surfaces.
Surfactants have significant effects on the properties of liquid-solid surfaces. The effects of surfactants on the surface-enhanced Raman scattering (SERS) of molecules adsorbed on solid substrates have been used to improve the qualities of SERS spectra and to reveal the distance-enhancement relationship of SERS. On the other hand, the adsorption behaviors of porphyrin compounds on surfaces are important for their applications in electrode modification, sensitization of photo-electric transduers and biomimetic catalysis. The effect of cetyltrimethyl ammoniumbromide (CTAB) on the SERS of free-base 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (H2TMPyP) and its Ag-chelate (AgTMPyP) adsorbed on Ag colloid was studied. It was found from the SERS spectra that the adsorbed H2TMPyP molecules undergo silver-incorporation to form AgTMPyP which can change back toH2TMPyPwhen added CTAB. The similar demetallization reaction was aslo observed in AgTMPyP/Ag sol/CTAB systems. The SERS signals were found to be obviously enhanced when added CTAB. The implications of the findings in relation to the change ofmicro-environmenton Ag particles by the addition of CTAB are briefly discussed.
The mixed-basis expansion of the wave-function together with the first-principles norm-conserving non-local pseudopotentials method has been used to study the electronic structures and geometric properties of CuSn under various structures, i.e. the NaCl-type, CsCl-type, Zinc-blende-type, WC-type, NiAs-type structures and tetragonal structure, which changes along the C-axis based on the CsCl structure. The relationship between the cohesive energies and the volumes of different structures, i.e. the energy-structure phase diagram, is presented. The result shows the NiAs-structure at low temperature is the most stable structure of CuSn. Furthermore, the band structures, electronic densities of states, charge density contour plots and bonding characters for CuSn crystallized in NiAs structure are also discussed. It is shown that the calculated stable phase for CuSn is consistent with the experiment result.
The geometry, electronic structure and frontier orbitals of bis-thinenyl-tetrathiafulvalene-C60(BTTTF-C60) and Tetrathiafulvalene-C60(TTF-C60) have been calculated by AM1 method. The results indicate that the geometries of BTTTF-C60 andTTF-C60 are curved. The curved geometry conformation is probably caused by the charge interaction between C60 and TTF, C60 and BTTTF respectively. Because the LUMO energy of C60 is close to the HOMO energy of BTTTF, the D-A reaction to BTTTF-C60 takes place easily. The LUMO energies in BTTTF-C60 and TTF-C60 are low and their orbitals distribution is mainly shown in C60 section, which means C60 section can still accept electrons. The analyses of charge population and molecular orbitals distribution, the property of BTTTF-C60 is similar to TTF-C60. A charge-separated state may occur in BTTTF-C60 when it is excited.
The mechanism of 2-amino-5-mercapto-1,3,4-thiadiazole(AMT) isomerization reactions have been studied by B3LYP/6-31+G** and the geometric parameters of reactants, products and transition states have been located at the same calculation level. The stationary points have been conformed by vibration analysis and zero-point energy corrections have been considered. The energy of the Qcisd(T) has been counted single point by single point and the way of IRC of the reactionary course has also been counted so that the possible channel of isomerization is determined. The obtained results show that there are sixtransition states occurring in the course of isomerization reactions for different isomers, among which the isomerization from A to C is the easiest one and C is the most stable one.
Based on the theoretical model of Rossler reaction system, a new dynamical system under external periodic perturbation modulation is constructed. The dynamical behavior of oscillatory state in the new system is investigated by using of the inverse operator method and the numerical analysis method because the inverse operator method is of high precision, quick convergence for the solution of nonlinear equations. The results show that the dynamical behavior of the system takes place notable changes and takes on many new evolution patterns under the external modulation of the periodic perturbation. For examples, the single periodic oscillation in the system which perturbation is not added is evolved to multi-period oscillatory states, such as period two (2P), period four(4P),…, 2nP and chaos when the system is modulated by periodic perturbation. It is found that the parameter of the perturbation phase (PP) is the most sensitive and the highest efficient in the modulation process if only one parameter is modulated while others are kept constant. In the same time, the new evolution patterns of the system (multi-period oscillatory state and chaos) will take on in the different numerical regions of the PP, and the small number change of the PP can influence internal construction of each evolution pattern although evolution patterns of the system don′t change.
According to the peak numbers of the nuclearmagnetic resonance and the Randic embranchment degree of the carbon atom, the carbon atom′s characteristic value is derived. A novel connectivity indexesm Y based on the adjacency matrix and the characteristic worth of the carbon atom is constructed. The zeroth-order connectivity indexes0Yamong the connectivity indexm Y are very easyto be calculated and have good discrimination between isomeric alkanes. The zeroth-order connectivity indexes0Yof 157 alkanes are calculated and correlated with the standard entropies of the alkanes, and the property iswell modeled (R=0.9985). It is concluded that the index0Ybearsgood structure selectivity and property relativity compared with Randic′s0χ and Ni Caihua′s topological information index which provids a valid method for predicting the standard entropies of alkanes.
Enlightened by the topological index mX of the Randic molecular connection, the author formed the topological index mF of electro negativity. Utilizing the zero and first order indexes of mF related with 20 kinds of alkali halide consisting of lattice energy, enthalpy of formation and hydrated energy, 51 kinds of ion hydrated heat and 80 kinds of ion standard heat of formation, the several regression equations were suggested. Their related coefficients (indexes) are 0.9954 (0.9954), 0.9835 (0.9840), 0.9794(0.9795), 0.9948 and 0.9865, which meet the good or excellent standards. The structure selectivity achieves its only expression. Hence the calculation gains satisfactory results.
The reaction-diffusion-convective equations with general diffusion and flow rates for Selkovmodel are established. Non-Turing instability (NTI) and its parameters space for the system are studied. Compared with the results by Andresen , the condition for the occurrence of non-Turing instability is extended. The stationary spatial periodic structures still exist outside the oscillatory Hopf domain. Therefore, the parameters space where NTI exists in this case is bigger than those by Andresen. Meanwhile, the relations of the parameters space of NTI with those of Tu ring instability and differential flow-induced instability are comparatively studied. It is shown that dynamical mechanism is caused by differential flow-induced instability (DIFI) instability, and DIFI is the necessary condition for flow-distributed structure (FDS) to occur.
The light-to-electricity conversion process of the TiO2 nanostructured electrode sensitized by an unsymmetrical cyanine dye (noted as CD) was investigated using the photoelectron chemical method. The results showed that the excited state level of the dye well matched the conduction band edge of TiO2 nanoparticles and the electron of the excited dye could be injected into the conduction band of TiO2 nanoparticles. A red-shift was observed in both the optical absorption and photocurrent spectra of the sensitized TiO2 nanostructured electrode compared with the unsensitized TiO2 nanostructured electrode. The maximum value of IPCE reached 84.3%. The process for the injection of electron into the TiO2 nanoporous film from the excited dye was studied with in situ spectroelectrochemistry. The results showed that the above process could be influenced by externally applied potential.
A sol-gel method was used to synthesizeNiFe2O4nanoparticles. The sol solution was prepared through nitrates dissolved in melted citric acid for 30 min by means of an ultrasonic cleaner, maintaining the molar proportion of iron and nickel equal to 2∶1 and joining a little PEG(polyethylene glycol) 200 as the dispersing agent. The sol solution was evaporated at 70℃ for 12 h to formwetgel, then dried at 110℃ in a drying oven for 24 h. The dried gel was annealed at different temperatures. Their composition and structure were measured in the synthesizing process using the infrared absorption-transmittance spectrum. The infrared diffuse reflection spectra and X-ray diffraction (XRD) spectra were measured for the specimens annealed at different temperatures. The average grain sizes were calculated from XRD spectra using Scheer′s equation. It was discussed for the effect of the NiFe2O4 nanoparticle size on infrared diffuse reflection spectra. The results show that the infrared absorption-transmittance spectra can reflect the changes of composition and structure in various stages from sol to heat-treatment and provide basis for the optimum annealed temperature in the synthesis of NiFe2O4with the sol-gel method. The grain sizes are different for the samples annealed at different temperatures and the annealed temperature must be more than 400℃for eliminating organic compounds completely. The higher the temperature, the bigger the grain size and the smaller the Kubelka-Mnnk function (K-M) values. In a certain range of grain sizes, the relationship of grain size and the logarithm of the K-M value is linear. When the grain size is big enough, the K-M value almost doesn′t change and the effect of grain size disappears.
Porous alumina membrane is prepared by aluminum anodizing in given acidic solution. Now porous alumina membrane is a type of the famous template for fabricating nano-structural materials. The method of two-step anodic oxidation improves the regularity of porous distribution greatly. For optimizing nano-structured assembling system, highly ordered porous alumina template is desirable. The cause of ordered porous aluminamembrane made by two-step anodic oxidation has been investigated. The regularity of holes arrangement in the membrane made by two-step anodic oxidation displayed better than that of the membrane anodizing only once from experimental results. The long-range ordered scope reaches 3~4μm. However, the ordered scope of holes arrangement in two-step membrane is limited in several micrometers and difficult to improve. In order to raise the order degree, aluminum was annealed to increase the grain size. The result showed that annealing had no contribution to holes ordering. In fact, the sub-grain size of aluminum decides the dimension of ordered scope.
The arachidic acids with Cerium 2,2,6,6-tetramethylheptanedionate were mixed at different ratios in chloroform solution and spread it onto pure water. The π-Aisotherm and the excess free energy of the mixed monolayer were studied. The miscibility, the molecular interaction of the two components and the probable condensed structure of the mixed monolayer were studied. It is found out that the Cerium 2,2,6,6-tetramethylheptanedionate/arachidic acid molar proportion of 1∶2 is the best for the formation of the stable mixed monolayer. The static elasticity and the dynamic elasticity of the mixed monolayer was also studied. It is found out that the interaction between the AA and the Ce(tmhd)4is significantly stronger and two AA molecules and one Ce(tmhd)4 molecule have formed agroup at a low surface pressure. Therefore the molecular arrangement is much closer and the mixed monolayer do not exist in the liquid state. The static elasticity and the dynamic elasticity of mixed monolayer are both enhanced especially at the low surface pressure.
The thermolytic process of serine is tested by thermogravimetry (TG), differential thermal analysis(DAT) and infrared spectrum (IR) methods. The thermolysis of the serine after the loss of the CO2 is very complicated and it is hard to obtain thermolytic reaction mechanism by experimental testing methods. Thus, the thermolytic reaction mechanism of serine is theoretically deduced by ab initio calculation method of quantum chemistry. The parameters of the total energy and Mulliken population are obtained by the optimized calculation on the geometries of serine, its thermolytic intermediate and final products respectively at the RHF/6-21G level. The calculation of epoxy intermediate is optimized by directly inputting into computer molecular fragments of serine after its loss of NH3. Oscillation analysis is made on the epoxy intermediate and the results indicate that the structure of epoxy intermediate is a stable structure, but not a non-saddle point transition state. The obtained results are consistent with what is stated in the documents concerned. However, in Ratliff′s documents, the production of epoxy intermediate in the thermolytic process of serine is only a supposition rather than based on either experimental test or theoretical deduction. Here the existence of epoxy intermediate is proved theoretically. Through the analysis of the results of the experiment and calculation, the thermolytic reaction mechanism is put forward: the thermolysis of serine is performed with the loss of CO2 as the main reaction channel and accompanied by the secondary reaction with the production of epoxy intermediate after the loss of NH3. Furthermore, a comparison is made between ab initio calculation method and semiempirical method. It′s proved that both methods can result in reasonable conclusion concerning the thermolysis of serine, however, the former has an advantage. In deducing the thermolytic reaction mechanism of serine by semiempirical method, not only is bond order used, but also localized orbital energy is required to judge the strength of bond. When bond order and localized orbital energy as criteria are contradicted with each other, the oscillation of bond is needed as subsidiary judgment. Thus, it is rather inconvenient to deduce the thermolytic reaction mechanism of serine by semiempirical method. On the other hand, by ab initio calculation method, only Mulliken population is needed as criterion to judge the strength of bond and reasonable conclusion can be reached just as well. What′s more, the research by ab initio calculation method can prove the existence of epoxy intermediate, which cannot be tested either by experiment or by semiempirical method.
The dehydration of Zn(CH3COO)2·2H2O has been studied isothermally and non-isotherm ally using TG method. The isothermal TG studies were carried out at the temperature of 61.1, 62.8, 66.2, 69.9℃. The activation energy was obtained by means of the lnt=E/RT+ln[g(α)/A]using the data at the same conversion rateα. Nonisothermal experiment was carried out at a rate of 10℃/min in 40 mL/minN2, Zn(CH3COO)2·2H2Odehydrated at 71~102℃. The data from nonisothermal experiment were analyzed by Doyle-Zsako method. Combined with the isothermal results the integral kinetic function g(α)=[-ln(1-α)]2/3 of the dehydration of Zn(CH3COO)2·2H2O activation energy 100.8 kJ/mol, preexponential factor ln(A/s-1)=36.09 and the kinetic compensation effect equation lnA=0.3339E+2.010 were found.