2006 Vol. 19, No. 5

Quasi-classical trajectory (QCT) calculations on the H++H2 reaction system were carried out on a new potential energy surface (PES). Theoretical calculations show that the angular distribution of the forward and backward products is roughly symmetric for the title reaction. The product rotational state distribution was also determined at a few collision energies. In the collision energy range from 0.124 eV to 1.424 eV, the integral cross section for this system monotonically decreases with the collision energy. A comparison with the experimental result of the ion-molecule reaction was also made, the agreement is generally good.
A comprehensive experimental study of the premixed ethylene/oxygen/argon flame at 2.667 kPa with a stoichiometric equivalence ratio (φ=1) was performed with the tunable synchrotron photoionization and molecular-beam sampling mass spectrometry techniques. The isomers of most observed species in the flame were unambiguously identified by measurements of the photoionization efficiency spectra, e.g. C3H4, C2H4O and C4H4. The mole fraction profiles of species up to C7H8 were measured by scanning the burner position at the selected photon energies near ionization thresholds, and the flame temperature profile was obtained by using Pt/Pt-13%Rh thermocouple. Compared with the previous studies, a lot of new flame species:C3H2, C3H3, C3H5, C2H6O, C4H2, C4H4, C4H6, C3H4O, C3H6O, C3H8O, C5H6, C4H8O and C7H8, were observed. A series of free radicals in the flame are detected to be CH3, C2H3, C2H5, HCO, C3H3 and C3H5.Based on the experimental work, a reduced reaction mechanism was developed including 40 species and 223 reactions. Modeling and measurements agree well for the major species and most intermediates. A detailed kinetic model is desired for this flame.
The radical-molecule reaction F+propene (CH2CHCH3) was studied in detail by using the Becke's three parameter Lee-Yang-Parr-B3LYP/6-311G(d,p) and coupled cluster with single, double, and triple excitationsCCSD(T)/6-311+G(2d,2p). It is shown that F+propene reaction mainly occurs through complex-formation mechanism: F attacks the double bond of propene leading to the formation of complex 1 and complex 2. As the two radical complexes are metastable, they can quickly dissociate to H+C3H5F, CH3+C2H3F and HF+C3H5. Based on the ab initio calculations, the CH3+C2H3F is the main channel, and the H elimination and HF forming channels also provide some contribution to products. The calculated values are in good agreement with the recently reported experimental results.
The geometrical and electronic properties of the anionic and neutral V2O6 clusters were studied with the spin unrestricted hybrid density functional B3LYP method. The calculated ground states of both clusters are different from the previous theoretical results. The ground state of V2O6- is found to be a doublet with C2v symmetry, while a doublet with D2h symmetry was previously obtained by Vyboishchikov and Sauer. For neutral V2O6, the ground state is an open-shell singlet with D2h symmetry whose energy is very close to that of the triplet state. In contrast, a closed-shell singlet with D2h symmetry was obtained by Vyboishchikov and Sauer, and Calatayud et al. found a triplet ground state with Cs symmetry. Moreover,the calculated adiabatic and vertical detachment energies of the anion cluster are in much better agreement with the experimental results of photoelectron spectroscopy than previous theoretical values.
The density function theory at the B3LYP/6-31G* level was employed to study the structures, including the total energies (EZPE), the geometries, the oxygen balances (OB100), the dipole moments, of polynitrohexaazaadamantanes (PNHAAs) and the potential candidates of high energy density compounds (HEDCs).The structural parameters of PNHAAs, such as the the maximum N-NO2 bond length (LBmax), the least N-N Mulliken population (BN-N), the least negative charge on the nitro group (QNO2) and OB100, were studied to predict their relative stability or sensitivity (the easiness for initiating a detonation, high sensitivity means low stability). It was found that the same conclusion was drawn from the four parameters.With the number of nitro groups increasing, the stabilities of these compounds decrease. OB100 failed in identifying the isomers, but the EZPE energy and the dipole moment were considered to give more reliable results for the isomers.
Density functional theory B3LYP method with 6-31++G** basis was used to optimize the geometries of the ground states for 1,2,3-triazine-(H2O)n (n=1,2,3) complexes. All calculations indicate that the 1,2,3-triazine-water complexes in the ground states have strong hydrogen-bonding interaction, and the complex having a N…H-O hydrogen bond and a chain of water molecules which is terminated by a O…H-C hydrogen bond is the most stable. The H-O stretching modes of complexes are red-shifted relative to that of the monomer. In addition, the Natural bond orbit (NBO) analysis indicates that the intermolecular charge transfer between 1,2,3-triazine and water is 0.0222e, 0.0261e and 0.0273e for the most stable 1:1, 1:2 and 1:3 complexes, respectively. The first singlet (n, π*) vertical excitation energy of the monomer 1,2,3-triazine and the hydrogen-bonding complexes of 1,2,3-triazine-(H2O)n were investigated by time-dependent density functional theory.
The B3LYP/LanL1 MB and B3LYP/LanL2DZ methods for Ag atom in conjunction with the 6-31G(d) basis set for S, C and H atoms were used to optimize the geometries and calculate the energies for (SCH3)mAg20 (m=1-4), resvectively. A single molecular adsorption energy of (SCH3)m (m=1-4) on Ag20 and the intermolecular substrate-mediated interaction energy were evaluated. The results revealed that there is a proportional relation between the single molecular adsorption energy and the substrate-mediated intermolecular interaction energy. The results qualitatively demonstrated the semi-empirical expression for the substratemediated interaction energy proposed previously by us is consistent with the results of the density functional theory.
Based on the vibrational potential curves coupled with the minimum energy reaction path, the partial potential energy surface of the reaction I+HI→IH+I was constructed at the QCISD(T)//MP4SDQ level with pseudo potential method. And the formation mechanism of the scattering resonance states of this reaction was well interpreted with the partial potential energy surface. The scattering resonance states of this reaction should belong to Feshbach resonance because of the coupling of the vibrational mode and the translational mode. With the one-dimensional square potential well model, the resonance width and lifetime of the I+HI(v=0)→IH(v'=0)+I state-to-state reaction were calculated, which preferably explained the high-resolved threshold photodetachment spectroscopy of the IHI- anion performed by Neumark et al..
Saturated vapor pressure was calculated from the nucleation experimental data using the thermodynamically consistent nucleation theory in which the effect of real gas is considered. The cubic polynomial fit equations of saturation pressure for several substances were obtained based on the calculation. The results of the calculations were compared to those of thermodynamic equilibrium equation and the empirical equation and applied to the predictions of the classical nucleation theory. The results show that the saturation pressures estimated from the nucleation data agree fairly well with those of empirical equations for the substances investigated, and this indicates that the predictions from the classical nucleation theory are close to the experimental data.
A new compound, 3S-hydroxy-7 melleine was isolated from the endophytic fungus Xylariasp No.2508 from the mangrove tree on the South China Sea coast. It was the first time that this kind of compound was isolated from marine fungus. The structure was elucidated by NMR data, infrared spectrum (IR) and mass spectrometry (MS). In addition, its structure was determined by the single-crystal X-ray diffraction analysis. It crystallized in monoclinic, space group P21 with a=10.8884(19) (A), b=7.2284(13) (A), c=13.398(2) (A), β=104.217(3)°,C10H10O4·H2O, Mr=212.20, V=1022.2(3) (A)3, Z=4, Dc=1.379 mg/m3, F(000)=448, μ=0.112 mm-1, the final R=0.0498, wR=0.101 for 2407 observed reflections (I>2σ(I)). The molecular backbone of the compound includes a benzopyran ring. By comparing with the melting point and the optical rotation of the known 3R-hydroxy-7 melleine in literature, the absolute configuration of the compound was determined as 3S. It didn't exhibit antibacterial activity against Gram-positive bacterium Staphylococcus aureus at 200μg/disk in the preliminary test.
Perovskite-type SrTiO3 nanoparticles were synthesized by direct hydrolysis-precipitation method and were employed to modify the surface of the carbon nanotubes to form a SrTiO3/CNTs composite. The photoelectrochemical lithium insertion characteristics of the SrTiO3/CNTs composite under xenon light irradiation were investigated. The results show that the light irradiation has little influence on the specific capacity of the CNTs electrode. However, for the SrTiO3/CNTs electrode irradiated by light, the lithium insertion capacity reaches about 251 mAh/g, much higher than that without light irradiation (170 mAh/g). Cyclic voltammetry test reveals that the light irradiation can remarkably increase the reaction currents of lithium insertion and extraction. This may be attributed to the photo-excited intercalation of Li-ions into the CNTs by the SrTiO3 photocatalyst when irradiated by light.
1,3-Dipolar cycloaddition of DTE-azomethine ylides (DTE: dithienyl-ethene) to C60 in refluxed toluene was used to synthesize novel dumbbell-type fullerene dimer 1. For the sake of comparison, the monoadduct 2 were also synthesized. The molecular geometries of these two compounds were determined by theoretical calculations with HF-3/21G method. UV-Vis and fluorescence experiments were carried out in solvents with different polarity at the room temperature. All the results indicated the existence of a photoinduced intramolecular electron transfer process between the donor and acceptor moieties.
Single-crystalline nanoplates of magnesium oxide were successfully synthesized through a calcinations route from the newly produced Mg(OH)2 precursors, which were directly prepared from the commercial bulk magnesium powders under a hydrothermal process in the absence of any additions. Scanning electron microscope (SEM) analysis indicated that the nanoplates were 2-6 μm in average width and about 80 nm in thickness.Transmission electron microscopy (TEM) images revealed that there was large quantity of nanopores with diameters ranging from 5 to 40 nm distributed in these nanoplates. The room-temperature photoluminescence (PL) spectrum of the nanoplates illustrated a strong blue emission band at 416 nm and a weak green emission band at 559 nm. Brunauer-Emmett-Teller (BET) analysis exhibited a feature of high surface of 127.21 m2/g for the products. The fabrication mechanism of the product was also discussed.
Micro-lens (ML) and Micro-lens array (MLA) are important optical components widely used in many fields;Soft-lithography, a vital little process technology, has its unique performance to produce ML and MLA;The cylinder and spherical MLA of polymethyl methacrylate (PMMA) were successfully obtained by micromolding inSoft-lithography. Some suitable experimental parameters in the process were discussed, and the imaging property of the MLA was also studied simply.
1H and 13C NMR chemical shifts were determined to investigate the interactions of acetone with a room temperature ionic liquid 1-hexyl-3- methylimidazolium bromide [C6mim]Br at various mole fractions. Changes in chemical shifts of hydrogen nuclei and of carbon nuclei with the acetone concentration indicated the formation of hydrogen bond between anion of the ionic liquid and methyl protons of acetone. The NMR results were in good agreement with the ab initio computational results.
The reaction mechanism of CH2F radical with HNCO was investigated by density functional theory (DFT)at the B3LYP/6-311++G(d,p) level. The geometries of the reactants, the intermediates, the transition states and the products were optimized. The transition states were verified through the vibration analysis.The relative energies were calculated at the QCISD(T)/6-311++G**//B3LYP/6-311++G(d,p) level. Seven feasible reaction pathways of the reaction were studied. The results indicate that the pathway (5) is the most favorable to occur, so it is the main pathway of the reaction.
The hydrogen adsorption properties and uptake capacities of the A, X and ZSM-5 types of zeolites were investigated at temperatures of 77, 195 and 293 K and pressures up to 7MPa, using a conventional volumetric adsorption apparatus. All hydrogen adsorption isotherms were basically type I, but the maximum in isotherm,a unique feature of supercritical adsorption, was observed at high pressures of 2-5 MPa at 77 K. The isosteric heats of adsorption were determined from the isotherms and the factors that influence their variations were discussed. Different types of zeolites exhibited remarkably different hydrogen uptake, based on both the framework structure and the nature of the cations present. The highest gravimetric storage capacity of 2.55wt% was obtained for NaX-type zeolite at 4 MPa and 77 K. In CaA, NaX and ZSM-5 types of zeolites,hydrogen uptakes were proportional to the specific surface areas, which were associated with the available void volumes of the zeolites. A threshold in hydrogen adsorption observed in NaA and KA was attributed to a pore blocking effect by large cations in KA. A ratio of the kinetic diameter of adsorbate to the effective opening diameter of zeolite was used to judge the blocking effect for physisorption.
In order to develop photoactive cobalt-doped TiO2 for the degradation of organic pollutants using visible light irradiation, the effects of cobalt precursor on TiO2 microstructure were investigated. Three cobaltprecursors, i.e. CoCl2, Co(NO3)2 and CoSO4 with two doping levels (nominally 1% and 10%), and two annealing temperatures (400 and 800 ℃) were adopted to prepare the doped titania through the sol-gel method. The powder samples were characterized with XRD, SEM, BET surface area analysis and UV-Vis absorption spectroscopy, and their photocatalytic activities were evaluated by the degradation of aniline under visible light irradiation. The results showed that the distribution of titania phases, particle size,morphology, surface area and the optical absorption of the catalysts were greatly dependent on the cobalt precursors. Samples prepared from Co(NO3)2, especially for those doped at 1% and calcined at 400 ℃,showed the highest photocatalytic activity towards the degradation of aniline, and the possible reasons are discussed briefly.