Thermal addition of xathenethione to allenes: “A Concerted Two Step” (π2s+π2s+π2s)-cycloaddition

(2+2)- and (4+2)-cycloadducts are formed by thermal reaction of xanthenethione with allenes. Activation parameters for ths “concerted two step” (_π2_s+_π2_s+_π2_s) reaction are presented.     

Bond function parameter transferability in SO2, SF2 and SO2F2

Ab initio MO studies of the use of gaussian bond functions in the molecules SO₂,SF₂ are presented. It is shown that optimization of bond function exponent and position parameters in the small molecules is a good approximation to the optimum parameter set for SO₂F₂,     

An ab initio study of the electronic structure of SiH4, SiH3F and SiH2F2

Changes in molecular properties and in the electronic charge distribution of the molecules SiH₄, SiH₃F and SiH₂F₂ are studied within the framework of the ab initio Hartree—Fock SCF—LCAO—MO method. The ionisation potentials, calculated with the use of Koopmans' theorem, correlate well with the experimental vertical ionisation potentials. The combined s and p electronic populations of the Si atom are not substantially altered when adding Si 3d functions to the basis set.     

Rydberg and valence-shell character as functions of internuclear distance in some excited states of CH,NH, H2, and N2

SCF MO computations have been carried out on several excited states of CH and NH in which the excited MO 4σ is a Rydberg or near-Rydberg MO at internuclear distances R near that (R_e) of equilibrium in the ground state, but becomes an antibonding valence-shell MO as R increases toward dissociation. For the lowest ³Π_g state of H₂ and the lowest ³Π_g and ³Π_u states of N₂ the extent of 3dπ Rydberg character in the excited MO as a function of R for some R values ? R_e is evaluated by SCF MO computations.     

The νs infrared absorption band profile of isotopically diluted oh groups in crystals

We show that Wojcik and Falk's stochastic theory of the ν_s(OH) band-shape in isotopically diluted ice in a special case of Robertson and Yarwood's treatment of the ν_s(OH) band-shapes of hydrogen-bonded species in solution. There is a lattice-dynamical reason why the band is narrow in ice.     

Structural order and disorder in Co-based layered cuprates CoSr2(Y,Ce)sCu2O5+2s (s=1-3)

Crystal structures of a homologous series of Co-based layered cuprates, CoSr₂(Y,Ce)_sCu₂O_5+2s (s=1-3), have been investigated by high-resolution electron microscopy (HREM) and electron diffraction (ED) techniques. For all the three phases ED patterns showed double periodicity along a direction parallel to the CoO layers, indicating a regular alternation of two types of CoO₄-tetrahedra chains within the layers. Also seen was ordering of the chains along the layer-stacking direction for the s=1 phase (Co-1212); ED patterns simulated based on the proposed superstructure model well reproduced the observed patterns. For the s=2 (Co-1222) and s=3 (Co-1232) phases in which an additional fluorite-type layer-block is inserted between two CuO₂ planes, HREM and ED analysis revealed complete disorder of the CoO₄ chains along the layer-stacking direction. This implies that the interlayer ordering is mainly controlled by the distance between the neighboring CoO layers.     

Transmission window in the νs (OD) band of hydrogen-bonded monodeuteromethanol

A study of the temperature evolution of the ν_s (OD) band of self-associated CH₃OD in solution shows clearly that the structure in this band is due to Fermi resonance with an infrared inactive overtone or combination. The degree of mismatch between the two interfering modes can be varied continuously over a substantial frequency range simply by changing the temperature.     

Structure of tetracoordinated sulphur compounds. Model calculations on SH4 and SF2H2

The structure of the hypothetical sulphuranes SH₄ and SF₂H₂ is investigated through ab initio LCAO MO SCF calculations. In contrast to a recent report the structure of lowest energy for SH₄ is of C_4V symmetry. For SF₂H₂ a structure of C_2V symmetry with axiai fluorine atoms is predicted. These results have been rationalized on the basis of perturbation theory.     

An ESR study of a hydrido-bridged trimetal cluster,Mn3(μ-H)3(CO)12−.

The anion radical of Mn₃(μ-H)₃(CO)₁₂ has been generated in frozen 2-methylte- trahydrofuran solutions by γ-irradiation and its ESR spectra have been analyzed. The spectra are consistent with D_3h geometry of the anion radical. The unpaired electron is accommodated in an a′₂; MO (D3h point group) constructed mainly from the manganese d AO's and with bent σ^★ characteristics with respect to the three MnMn bonds. The spin densities on the manganese d AO's and on the hydrogen 1s AO are estimated as 0.21 and ?0.03, respectively. The g tensor is explained using an MO diagram constructed from a model of the protonated metal-metal bond for the MnHMn bonds.     

Kinetics of the reaction of NH2 with NO2

The absolute rate constant of the reaction of NH₂ with NO₂ has been measured using a flash-photolysis laser resonance-fluorescence technique. The value obtained at room temperature is k₁ = 2.3 (± 0.2) × 10^?11 cm³ molecule ^?1 s^?1. A negative temperature coefficient has been found between 298 and 505 K for this reaction, k₁ = 3.8 × 10^?8 × T^?1.30 cm³ molecule^?1 s^?1. It is thought that this is the major reaction of NH₂ in the troposphere.     

Anomalous electronic energy partitioning in Mg*(3p) + (F2, Cl2) and Ca*(3P) + Cl2 reactions

Absolute cross sections were measured for beam attenuation, MX⁺(¹Σ_g⁺) chemiionization and MX(A²Π) chemiluminescence. The latter disagree strikingly with predictions based on adiabatic correlations. Information theoretic analysis shows some channels to be statistically, other highly non-statistically populated. A qualitative MO model is in accord with these findings.     

Structural behavior and thermoelectric properties of the brownmillerite system Ca2(ZnxFe2−x)O5

The Ca₂(Zn_xFe_2−x)O₅ series was synthesized and characterized to determine the influence of zinc dopant on the brownmillerite structure for thermoelectric applications. All single-phase compounds exhibited Pnma symmetry at room temperature up to the solubility limit at x=0.10. High-temperature X-ray powder diffraction was used to show that the nature of the Pnma-Imma(0 0 γ)s00 transition in Ca₂Fe₂O₅ is modified by the presence of zinc. While the Zn-free composition transitions to an incommensurate phase, the Zn-containing phases transition instead to a commensurate phase, Imma(0 0 γ)s00 with γ=1/2. Both the Néel temperature and the onset temperature of the Pnma-Imma(0 0 γ)s00 phase transition decreased with increasing zinc concentration. Rietveld analysis of the in situ diffraction pattern for the x=0 sample at 1300 °C demonstrates that the structure contains statistically disordered chain orientations as described by space group Imma. Thermoelectric properties were analyzed in air from 100 to 800 °C. The positive Seebeck coefficient revealed hole-type conduction for all compositions. Doped samples exhibited electrical conductivities up to 3.4 S/cm and thermal conductivity of 1.5 W/mK. Transport analysis revealed thermally activated mobility consistent with polaron conduction behavior for all compositions.     

Reactions of HO2 with NO,OH and HO2 studied by EPR/LMR spectroscopy

A combined EPR/LMR spectrometer and fast-flow system has been used to investigate the reactions HO₂ + NO(k₁), HO₂ + OH(k₂), HO₂ + HO₂(k₃) at room temperature. The rate constants have been measured: k₁ = (7.0 ± 0.6) × 10^?12 cm³ s^?1 (P = 7–10 Torr);k₂ = (5.2 ± 1.2) × 10^?11 cm³ s^?1 (P = 8–10 Torr);k₃ = (1.65 ± 0.3) × 10^?12 cm³ s^?1 (P = 2.1–24.9 Torr). The conclusion is drawn from analysis of the literature and the present work that k₂ and k₃ do not depend on pressure up to 1 atm.     

Oxidative addition of dihydrogen to Ni(II) complexes.ab initio MO/MP4 calculations of the electronic structure of NiH2Cl2(PH3)2 complex

Electronic state d⁶ Ni(IV) in the complex [NiH₂Cl₂(PH₃)₂] was studied by means ofab initio MO/MP4 calculations.     

Electron scattering differential cross sections for C2H2, C2H4, and C2H6 by gas phase electron diffraction - binding effects

Experimental differential cross sections for 40 keV electrons scattered by C₂H₂, C₂H₄ and C₂H₆ molecules were measured using the gas electron diffraction method in the range of the scattering variable s from s = 1 A^?1 to s = 30 A^?1. The differential cross sections for neon were also measured and compared with calculated differential cross sections to calibrate the diffractograph. Experimental differential cross sections show significant deviations with respect to theoretical differential cross sections calculated from the Debye-Ehrenfest model, mainly in the range of small scattering angles. The observed differences are connected to chemical binding effects. From the experimental data, an estimation of the binding energy was carried out. The deduced values: ?0.58 ± 0.20 au for C₂H₂, ?0.94 ± 0.30 au for C₂H₄ and ?1.23 ± 0.40 au for C₂H₆ are in agreement with those obtained by thermochemical methods.     

花状CeO2/TiO2异质结的构筑及光催化性能

采用溶剂热法制备了三维花状CeO₂/TiO₂异质结光催化剂,然后以甲基橙(MO)为模拟有机污染物,在氙灯照射下考察了其光催化活性。结果表明,花状结构由纳米片和纳米颗粒复合而成,纳米片上均匀地附着CeO₂颗粒。Ce/Ti的物质的量之比(n_Ce/n_Ti)和溶剂热时间影响异质结的光催化性能,当n_Ce/n_Ti=0.1、溶剂热时间为6 h时,CeO₂/TiO₂的光催化活性达到最佳,氙灯照射50 min的降解率达95%,光催化活性优于纯TiO₂,这主要是CeO₂和TiO₂形成了异质结,有利于光生电子和空穴的分离。     

The mechanism of SO2 oxidation by CH3O2 radicals. Rate coefficients for the reactions of CH3O2 with SO2 and NO

The reactions of CH₃O₂ with SO₂ and NO have been studied by steady state photolysis of azomethane in the presence of O₂SO₂→NO mixtures at 296 K and 1 atm total pressure. The quantum yield of NO oxidation by CH₃O₂ radicals is increased substantially when SO₂ is added to the system indicating an SO₂ induced chain oxidation of NO. The rate law gives k₁/k₂ = (2.5 ± 0.5) × 10^?3 for CH₃O₂ + SO₂ → CH₃O₂SO₂ (1), CH₃O₂ + NO → CH₃O + NO₂ (2). Combining this ratio with the absolute value of k₁ = 8.2 × 10^?15 cm³ s^?1 gives k₂ = 10^{?11.5 ± 02} cm³ s^?1.     

The protonation and hydrogen transfer processes in alkene and alkyne derivatives of Os3 and H2Os3(CO)10

The complexes H₃O_s3(CO)₉CMe, H₂O_s3(CO)₁₀, H₂O_s3(CO)₉L (L = PEt₃, PPh₃ or AsPh₃), HO_s3(CO)₁₀CHC(H)Ph, and O_s3(CO)₁₀HC₂Me undergo protonation in acid to yield [H₄O_s3(CO)₉CMe]⁺ and [H₄O_s3(CO)₁₀]²⁺, [H₃O_s3(CO)₉L]⁺, [H₂O_s3(CO)₁₀CHC(H)Ph]⁺ and [HO_s3(CO)₁₀HC₂Me]⁺, respectively. The structure of these ions and their hydrido-ligand transfer reactions are described.     

Upper limits for the rate constant for the reaction Br + H2O2 → HBr + HO2

Upper limits for the rate constant for the reaction Br + H₂O₂ → HBr + HO₂ have been measured over the temperature range 298 to 417 K in a discharge flow, system using a mass spectrometer as a detector. Results are K₁< 1.5 × 10^?15 cm³ s^?1 at 298 K and K₁< 3.0 × 10^?15 cm³ s^?1 at 417 K, respectively. The implication to Stratospheric chemistry is discus     

Absolute Rate constants for O + No + N2 → NO2 + N2 from 217–500 K

Flash photolysis of NO coupled with time resolved detection of O via resonance fluorescence has been used to obtain rate constants for the reaction O + NO + N₂ → NO₂ + N₂ at temperatures from 217 to 500 K. The measured rate constants obey the Arrhenius equation k = (15.5 ± 2.0) × 10^?33 exp(1160 ± 70)/1.987 T] cm⁶ molecule^?2 s^?1. An equally acceptable equation describing the temperature dependence of k is k = 3.80 × 10^?27/T^1.82 cm⁶ molecule^?2 s^?1. These results are discussed and compared with previous work.