2002 Vol. 15, No. 5

Article
The spectra of the (12,6), (11,5) and (7,2) bands of theA2Πu-X2Σ+gsystemand the (1,5) band of the B2Σ+u-X2Σ+gsystem of N2+have been observed and analyzed in the visible region between 16800~17573 cm-1using optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy. This paper has derived the effective Hamiltonian matrixes including the perturbation terms for analysis of the rovibronic spectrum in a diatomic molecule, revealed and explained the mechanism of the perturbation between the A2Πuand B2Σ+ustates of N2+. The analysis shows that the vibronic levels A2Πu (v=11) and B2Σ+u (v=1) have a strong interaction atJ=13.5 (for elevel) and 9.5 (for flevel). As a result, the perturbation constantsξeandηeforA2Πuand B2Σ+ustates ofN2+are obtainedwith the values of -34.1350 (59) cm-1and 1.09756(30) respectively.
The gas phase reactions of Al+ and Mg+ with acetonitrile are studied by laser ablation-molecular beam method. According to the results of reflectron flight time mass spectrometer (RTOF-MS) , Al+ and Mg+ react with acetonitrile to form different sized cluster ion products. A series of cluster complex ions Al+(CHCN)n(n=1~10) can be found and cluster complex ions Mg+(CHCN)n(n=1-5) are produced. The appearances of the complex ions Al+ (CHCN)n and Mg+(CHCN)n is obviously sensitive to the kind and pressure of rare gas used for the seeded acetonitrile beams. The phenomenon can be explained by the γ effect and the thermal accommodation coefficient. In laser ablation molecular beam experiments, Ar has a larger γ effect and a larger accommodation coefficient than He, so the former is Favor able for acetonitrile cluster growth. The energy of laser beams is an important factor which influences the size of clustered complex ions. According to the result of experiments, the energy of laser beams which can be controlled around or less than 2 mJ/pulse was favorable for forming clustered complex ions. Generally, decreasing laser energy can generate low energy metal ions. Although metal ions have rather wide kinetic energy (KE) distribution in LAMB experiments, only the low-energy portions of metal ions are effective in the reactions in their experimental configuration with the M+ flow and the molecular beam perpendicular to each other. The signal intensities of clustered complex ions Al+(CHCN)n and Mg+(CHCN)n show irregular distribution. For Al+(CHCN)n, the first intensity gap appears between n=4~5, and the second intensity gap is found between n=6~7. But for Mg+(CHCN)n, the intensity gap appear between n=2~3. The intensity gaps of Al+(CHCN)n and Mg+ (CHCN)n are relative to the binding energy of metal cation-orginic ligands. It is believed that the binding energy between Al+ and the fourth CHCN ligand is obviously higher than that between Al+ and the fifth CHCN ligand. Therefore, the intensity gap found in the present study indicates that the first coordination sphere for Al+ is completed at n=4. The fifth CHCN ligand and the sixth CHCN ligand must be loosely coordinated with the central Al+. Association reactions and dehydrogenation reactions are the two principal reaction pathways when metal ions react with organic ligands in LAMB experiments. When Al+ and Mg+ interact with (CHCN)n(n≥3), only the clustered complex ions Al+(CHCN)n and Mg+(CHCN)n can be formed through association pathways. However, when Al+ and Mg+ coordinate with one acetonitrile or two acetonitriles, not only Al+(CHCN)n(n≤2) and Mg+(CHCN)n(n≤2) can be produced through association reactions, but also Al+(CH2CN)n(n≤2) and Mg+(CH2CN)n(n≤2) can be formed through dehydrogenation reactions.
The thermal decomposition of 1,2-dichloroethane is studied in a heated single pulse shock tube. The shock wave temperature is 1020K
We present a new iterative method for the analysis of data obtained by imaging techniques. This method is based on a detailed investigation for the motion of charged particles in ion imaging apparatus. The conventional inversion approach is a good approximation only in the case of small kinetic energies of the charged particles. The iterative method has been employed to study the photoelectron spectrum of iodine atoms via intermediate state 3P0 by using 278.5nm laser. We got a relative energy resolution of 3.9% and found the photoionization involves two different passways corresponding to 3P0→3P0 and 3P0→3P1 respectively.
Both negatively and positively charged colloids (in brief, PCS and NCS) of silver nano-particles were prepared. Quenching and enhancement of fluorescence fromrhodamine (RhB) and Fluorescein sodium (FS) molecules on the two colloids of silver nano-particles were recorded respectively and compared with each other. On PCS, the fluorescence of RhB is enhanced when the concentration is low, whilst when the concentration is high the fluorescence of RhB is quenched. However for FS, the fluorescence is always enhanced. On NCS, the fluorescence of FS and RhB are quenched.
The molecular structure of nitro furazan compounds was described by a nove molecular sub-graph. In this coding method, furazan is considered to be the main-grap and cyano-are dismembered into atoms such as carbon, hydrogen, oxygen and nitrog atoms), which are the sub-graph. For a furazan compound, the formation heat is depend carbon-carbon double ortriple bond, the numbers of nitryl, ring (unless furazan ring), n gen double bound, and soon. It has been shown that there exists very good correlation be tion heats of nitro furazan compounds. The correlation coefficient (R) of MLR equation f relation(QSPR) on the formation heats nitro furazan compounds is 0.9954.
The cations of sulfur clusters exhibit intensities of significance on the mass spectra of sulfur clusters generated in direct laser vaporization. To our knowledge, theoretical investigations on cationic sulfur clusters are rare. Forty-nine isomers of sulfur clusters were acquired by means of the molecular model design, molecular mechanics and semi-empirical PM3 and the recently proposed and widely used B3LYPhybrid, non-local, DFT method with basis set 6-31G*. To look for stable configurations, full geometry optimizations at the 6-31G* level for all sulfur atoms were performed using Gaussian 98 program packages. The initial models were constructed by means of breaking bond(s), making bond(s), adding atom(s), deleting atom(s), rotating fragment(s), translating fragment(s) and merging fragment(s). The one-fold, twofold and three-fold modes for modeling were considered, according to the bonding characteristics of the sulfur atom. Finally a total of eleven structures forS3+, S4+and S5+; ten isomers of S6+and S7+; fifteen isomers of S8+ and S9+ and thirteen isomers of S10+, S11+, S12+and S13+are acquired, respectively. A large number of structural possibilities of non-minimum structures were not covered. According to total energies, the most stable Sn+ (n=3~13) isomers are predicted. The geometry, relative stability and structural rules of these cationic sulfur clusters were described. Some structures of neutral sulfur clusters with true minima transform upon ionization into non-minimum cationic structures and vice versa. The results of a large amount of calculations show that the two-fold coordination is generally favored in sulfur cationic clusters, though some sulfur atoms coordinated with the others in one-fold or three-fold mode are higher in total energy. The most stable isomer of some cationic clusters shows a structure completely different from that of the corresponding neutral cluster. In chain structures, the atoms at the two ends adopt the one-fold mode and the others are in two-fold mode. Theoretical studies on sulfur cationic structures with a three-fold atom are rare. It is unlikely to have a sulfur cationic cluster in cage structure, for the bonding of a three-fold atom are not strong enough. The calculation results can serve as guiding factors for future theoretical studies on large sulfur clusters.
This paper presents a new theoretical model for accurately calculating reorganization energy for electron transfer reactions. The process of electron transfer is divided into six steps, and the energy change of every step can be calculated byab initio. The structure of reactant and transition states in benzene nitride reactions is optimized on the level of CISD/6-31GusingGaussian 94. The inner-sphere and out-sphere reorganization energy of self-exchange reactions ArH+ArH+→ArH++ArH, O2++NO2→NO2+NO2+ and NO++NO→NO+NO+is obtained in terms of the proposed reorganization model. The reorganization energy of cross electron transfer reaction ArH+NO+→ArH++NO and NO2++NO→NO2+NO+is also obtained. The comparison of the theoretical values and the experimental values for the reorganization energy indicates that the inner-sphere reorganization energy of reactions inNO2++NO2→NO2+NO2+is larger than that in NO++NO→NO+NO+. While there exists little opportunity of electron transfersteps usingNO2+as an oxidizing agent, it is more possible that NO+ can be used as an oxidizing agent in the reaction of benzene because of the activation energy in proportion to the reorganization energy.
The potential energy surface of nitromethane (CH3NO2), including 10 CH3NO2isomers and 23 inter-conversion transition states, is probed theoretically at G2MP2//B3LYP/6-311++G(2d,2p) level of theory. The geometries and relative energies for various stationary points are determined. Based on the calculated G2MP2 potential energy surface, the possible nitromethane isomerization mechanism is discussed. The results are shown that the energy order for these 10 CH3NO2isomers is IS6>IS5>IS3>IS8>IS2>CH3NO2>IS4>IS10>IS9>IS7. The energy of IS7b (HC(O)N(H)OH) is the lowest, 111.7 kJ/mol below the nitromethane (CH3NO2), while the energy of IS6C (HCN(OH)2) is the highest, 240.6 kJ/mol above the nitro methane (CH3NO2). It is shown that CH3NO2isomerizations at the initial reaction stages are of high activation barriers. Among them, the respective nitromethane→methyl nitrite and nitro methane→aci-nitromethane barriers are 270.0 and 267.5 kJ/mol, higher than the C-N bond dissociation energy for CH3NO2. Our results suggest that nitromethane isomerization pathways are kinetically disfavored.
Cyclodextrins (CDs) are cyclicoligomers of D-glueose and named α-, β-, γ-CD for hexamer, heptamer and octamer, respectively. Owing to its special structural character, they formed inclusion complexes with various types of organic molcules in aqueous solution and attracted the curiosity of chemists and biologists since they could be regarded as artificial receptors. Some cyclodextrin molecules were modified with functional groups in orderto improve the properties in complexation and catalysis. The present parper report the quantum chemistry studies on 5 nitrogen containing group modified β-cyclodextrins. The results of geometry optimization showed that the location of modified functional group in molecular structure is vastly influenced by its volume. The physicochemical information was obtained by single point energy calculations. This heuristic calculation can also be used as a predicted method for new synthesis of modified cyclodextrins. The computational chemistry is therefore both an independent research tool and a vital adjunct to cyclodextrin experimental studies.
Motivated by recent applications to experiments on molecular motors, the directed motion of molecular motor based on a periodic one-dimensional three-states hopping model is studied. The model combines the biochemical cycle o nucleotide hydrolysis with the motor′s translation. An explicit solution is obtained for the probability distribution as function of the time for any initial distribution with all the transients included, and the drift velocity v, the diffusion constant D and the randomness parameter can also be obtained at any time from the probability distribution. Meanwhile the characteristic time for the motor to reach steady state has been calculated. Lastly, several possible applications arproposed: the pure asymmetric case, the random symmetric case and the random asymmetric case. In the long-time limit, the drift velocity v and the diffusion constant D are obtained in terms of microscopic transition rates that are parameters in the three-state stochastic model for the pure asymmetric case. By comparison with experiments (drift velocity and randomness parameter rversus [ATP]), it is shown that the model presented here can rather satisfactorily explain the available data. The theoretical model provides a conceptual framework for realistic studies of molecular motor.
Conclusion of structural stability requesting uniform distributions of molecular 38oand 98oorientational states is obtained by investigating the thermodynamic properties of C60crystal in ordered phase, based on a two-level energetic system formed by molecular rotations. At any temperature, the structural equilibrium is restricted by the minimum of free energy, which requests the 38oorientational molecules should distribute among the 38oorientational molecules equably and could not accumulate in the space to forma single sub-system in thermo-equilibrium. According to the reported experimental results of orientational occupancies at two edges of ordered phase 85 and 260 K of C60crystal, which can be accurately expressed as 1/6 and 3/8, the cubic molecular orientational distributions at two temperatures are acquired. When temperature rises, the increase of 38oorientational molecules is not simply the change from 98oorientational molecules to 38oorientational molecules, but a change in the whole structure to ensure the uniformity of 38oorientational molecules among the majority of 98oorientational molecules. In a single C60-molecule, there exist electron-rich regions and electron-pool regions. Two kinds of regions influence the interaction of twomolecules and produce electric dipoles. In sc phase, the magnitude of electric dipole will increase with the rise ofB(T), and will express as the increase of dielectric constants, i.e. the more 38oorientational molecules, the larger the dielectric constant. The uniform distribution of local electric charges varies with the orientational change among molecules. So, there are several regular systematic uniform distributions for 38oorientational molecules in the whole crystal over the 90~260 K temperature range. Orientational occupancies of 1/4 and 1/3 are the special points like two transition points, orientational occupancies of 1/6 and 3/8. Orientational occupancies of 1/4 and 1/3 in C60crystal have more structural stability and less dielectric dissipation at correspondent temperatures of 122.6 and 194.3 K, which can explain the anomalous behavior in dielectric dissipation and can be described as the uniform distribution of ”symmetry-asymmetry-symmetry”.
We report the preparation of nano-nickel particles embedded in poly(methyl methacrylate) matrix in situ by using radiation reduction of nickel ions and radiation induced polymerization of methyl methacrylate simultaneously with Co-60γ-ray. The size, morphology and structure of the nickel-poly(methyl methacrylate) nanocomposites were investigated by X-ray powder diffraction(XRD) and transmission electron microscopy(TEM) analysis and IR spectrum. XRD pattern of nickel-poly(methyl methacrylate) shows that the products are face-centred cubic(fcc) crystalline nickel by the diffraction peaks with 2θvalues of 44.3oand 52.3o, corresponding to the crystal faces of (111) and (200) of fcc crystalline nickel. According to Scherrer′s equation, the mean size of the nickel particles was calculated to be about 7.33 nm. From the IR spectrum of the nanocomposites, it can be seen that the double bond of methyl methacrylate dispeared after irradiation (1640 cm-1) and to be formed polymer. As seen from the TEM image of the sample, the nickel powders consisted of uniform size spherical particles, but small particles had aggregated into secondary particles due to their extremely small dimensions and high surface energy. Therefore, it was difficult to determine precisely the size and the size distribution of the nano-particles by simply viewing theTEM image. Sodium acetate was used as the basic agent, instead of NaOH or NH3·H2O. It can be used to control the pH value of the experimental solution, and does not affect the polymerization of methyl methacrylate. In summary, nickel-poly(methyl methacrylate) nanocomposites have been successfully prepared in one step by γ-irradiation in a heterogeneous system under ambient pressure at room temperature.
A fabrication technique of component-controllable multi-component ultra thin ceramic films has been developed by a promising LB method. The precursorofY2O3-stablized ZrO2(YSZ) ultra thin film was prepared with ZirconiumIV2, 2,6,6-tetramethylheptanedionate (Zr(tmhd)4) and yttrium 2,2,6,6-tetramethylheptanedionate (Y(tmhd)3) as surface ions on the subphase surface instead of traditional subphase ions. Zr(tmhd)4) and Y(tmhd)3can combine arachidic acid (AA) to forma uniformmixed monolayeron pure water subphase. The π~Aisotherms indicate that the mixed monolayer with a mixed ratio of Zr(tmhd)4∶Y(tmhd)3∶AA=4.5∶1∶11 on pure water is very stable and can be successfully transferred onto the silica substrate by LB technique. Y-type LB films were fabricated. The YSZ films were obtained through a combination of room temperature Ultra-Violet/ozone (UVO) decomposition and annealing treatments at a high temperature. The X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements demonstrate that the fina films are single YSZ phase with a fluorite cubic structure and the components of the films can be accurately controlled through the whole process.