Gas‐phase equilibrium constants for the thermally initiated oxidation of hexafluoropropene with molecular oxygen

Equilibrium constants for a kinetic model of the thermally initiated gas‐phase oxidation of hexafluoropropene have been calculated in the temperature range of 463–493 K based on the thermochemical properties of the reactive species. Standard molar enthalpies and entropies of formation as well as heat capacities of trifluoroacetyl fluoride, hexafluorocyclopropane, hexafluoropropene, and hexafluoropropene oxide were predicted using methods of quantum statistical mechanics. These along with literature data for remaining species involved allowed for calculating reaction enthalpies of individual steps of the proposed reaction mechanism. The calculations were performed at the G4 B3LYP/6‐31G(2df,p) level of theory. The enthalpy of formation was determined using both the atomization method and isodesmic reaction schemes. All reactions apart from the decomposition of hexafluoropropene oxide were found to be exothermic. Only the hexafluoropropene oxide decomposition reaction was found to be noticeably reversible under the reaction conditions considered. This was confirmed through independent experimentation and kinetic model identification. Copyright © 2015 John Wiley & Sons, Ltd.     

Transformations of mixed molybdenum-vanadium oxides in the oxidation of hydrocarbons by molecular oxygen

Structural-morphological transformations of molybdenum-vanadium mixed oxide catalysts of varying composition in the oxidation of hydrocarbons are studied by X-ray diffraction analysis, electron microscopy, electron paramagnetic resonance technique, and Raman scattering spectroscopy. It is shown that the catalytic reactions, which are analyzed in detail for oxides of various compositions, cause a considerable restructuring of the mixed oxides.     

Kinetics of the oxidation of 2-Propanol with molecular oxygen under conditions of selective inhibition

The specifics of the mechanism of chain propagation in the radical-chain oxidation of 2-propanol at 323 K were studied by the method of selective inhibition with the use of nitrobenzene and ionol. The rate constants for the interaction of the 1-hydroxy-1-methylethylperoxy (k _2.1 = (0.097 ± 0.004) L mol^?1 s^?1) and hydroperoxy (k _2.2 = 0.13 ± 0.05 L mol^?1 s^?1) radicals with alcohol and their relative contributions to the chain propagation reactions were determined.     

The mechanism of oxidation of FeS nanoparticles by molecular oxygen and hydrogen peroxide in dilute aqueous solutions

The kinetic characteristics of the oxidation of iron monosulfide with molecular oxygen and hydrogen peroxide in a neutral aqueous medium were studied. The rate of oxidation of FeS with oxygen was proportional to the concentration of O₂ and quadratically depended on the initial concentration of FeS, W ₀ = k _ef [FeS]²[O₂], where k _ef = (2.5 ± 0.5) × 10⁵ M^?2 s^?1 (pH 8, 22°C). During the oxidation of FeS, the iron ion retained the valence state +2. Oxidation products contained about 50% elemental sulfur. The interaction of FeS with H₂O₂ was characterized by the half-time of reaction less than 15 s. The products of oxidation of initially nontoxic FeS contained toxic compounds, supposedly the sulfoxylate ion HS ₂ ^? .     

Asphaltene radicals and their interaction with molecular oxygen: an EPR probe of their molecular characteristics and tendency to aggregate

The paramagnetic species nature of different geological origin asphaltenes are discussed on the basis of Electron Paramagnetic Resonance (EPR) results. Free organic radicals are present in petroleum asphaltenes but their molecular nature is poorly known owing to the multiplicity of their molecular structures which causes the appearance of a single unresolved EPR signal with a linewidth of 4–6 Gauss. In spite of the poorly resolved signals the microwave power dependence of EPR line intersities gives some insights into the nature of the aromatic rings condensation. More aromatic asphaltenes show higher saturation power of the EPR lines: this fact has been explained by a spin exchange mechanism between π-π electronic clouds of adjacent molecules, supported also by some XRD evidences. Moreover, asphaltenes in argon (not paramagnetic gas) show a maximum intensity at much lower microwave power than in oxygen atmosphere (paramagnetic gas); besides, the differences in the saturation behavior for the different asphaltenes are much more evident in oxygen atmosphere. This phenomenon is suggested to be a consequence of a weak spatial complex between aromatic moieties and oxygen molecules that deeply contribute to the relaxation pathway. Synchronous fluorescence spectroscopy confirms the difference in the size of aromatic cores in asphaltenes molecules as supposed on the basis of the saturation mechanism of EPR line intensities.     

2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面的裂解机理

本文研究了2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面解离的可能微观反应机理,使用完全线性同步和二次同步变换(complete LST/QST)方法确定解离反应的过渡态.采用基于第一性原理的密度泛函理论与周期平板模型相结合的方法,优化了2-丙醇和1,1,1-三氟-2-丙醇裂解反应过程各物种在Ni(100)表面的top,hollow和bridge位的吸附模型,计算了能量,并对布局电荷进行了分析,得到了各物种的有利吸附位.结果表明:2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面都存在β-H和γ-H两个平行竞争的解离过程,其中2-丙醇在Ni(100)表面β-H解离的速控步骤活化能为64.7 k J·mol-1猯,而γ-H解离速控步骤活化能为233.1 k J·mol-1猯,故β-H解离过程占优势,主要产物是CH3COCH3;相反,1,1,1-三氟-2-丙醇在Ni(100)表面β-H解离的速控步骤活化能为257.1 k J·mol-1猯,而γ-H解离速控步骤活化能为148.1 k J·mol-1猯,故γ-H解离过程占优势,主要产物是CF3CH=CH2.由此说明,电负性更大的氟原子取代2-丙醇中的氢原子之后,2-丙醇在Ni表面的解离机理发生了改变.理论预测结果与实验结论一致.     

2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面的裂解机理

本文研究了2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面解离的可能微观反应机理,使用完全线性同步和二次同步变换(complete LST/QST)方法确定解离反应的过渡态。采用基于第一性原理的密度泛函理论与周期平板模型相结合的方法,优化了2-丙醇和1,1,1-三氟-2-丙醇裂解反应过程各物种在Ni(100)表面的top,hollow和bridge位的吸附模型,计算了能量,并对布局电荷进行了分析,得到了各物种的有利吸附位。结果表明： 2-丙醇和1,1,1-三氟-2-丙醇在Ni(100)表面都存在β-H和γ-H两个平行竞争的解离过程,其中2-丙醇在Ni(100)表面β-H解离的速控步骤活化能为64.7 kJ∙mol-1,而γ-H解离速控步骤活化能为233.1kJ∙mol-1,故β-H解离过程占优势,主要产物是CH3COCH3;相反,1,1,1-三氟-2-丙醇在Ni(100)表面β-H解离的速控步骤活化能为257.1 kJ∙mol-1,而γ-H解离速控步骤活化能为148.1kJ∙mol-1,故γ-H解离过程占优势,主要产物是CF3CH=CH2。由此说明,电负性更大的氟原子取代2-丙醇中的氢原子之后,2-丙醇在Ni表面的解离机理发生了改变。理论预测结果与实验结论一致。     

On the oxidation of CaF2 in transmission electron microscope

Electron stimulated oxidation of CaF₂ in transmission electron microscope has been thoroughly studied using various electron microscopy techniques, including imaging, electron diffraction and electron energy-loss spectroscopy. It found that the electron irradiation induced CaO locate on the edge of specimen. The oxidation process is associated with desorption of F by electron irradiation, and originates from O impurities in the specimen. Driven by electric field produced by electron irradiation, the O ions inside bulk diffuse to the edge region, occupying the interstitials of metallized Ca lattice. Therefore, the accumulation of O along the edge of specimen results in forming CaO.     

XPS study of SnTe(1 0 0) oxidation by molecular oxygen

The interaction between the (1 0 0) surface of SnTe single crystal and molecular oxygen was studied by means of X-ray photoelectron spectroscopy (XPS). Analysis of the obtained spectra shows that the mechanism of surface oxidation does not change in the range of oxygen exposure 10⁸-10¹³ L. During the oxidation an additional component shifted 1.1 eV towards higher binding energies appears in the Sn 3d spectra. The Te 3d_5/2 spectra fitting reveals two additional components with binding energies close to Te⁰ and Te⁺⁴. The dependence of the additional components fraction in both Sn 3d and Te 3d_5/2 spectra on the oxygen exposure is semi-logarithmic. On the base of the experimental data two possible mechanisms are proposed.     

On the classes of integral equations nonderivable by graph theory means: An improved molecular theory for classical liquids in equilibrium

Starting from the definition of molecular distribution functions a new hierarchy of integral equations for the equilibrium classical liquids is derived. An outline is given of why this hierarchy cannot be derived by graph theory means. In the theory, the sum of elementary diagrams is given explicitly as a functional of the higher order correlation functions. Analysing this functional the most general truncation scheme within the framework of the first order theories is presented. The pairwise additivity of the intermolecular potential is not assumed.     

Fluorescence quenching of water-soluble porphyrins by molecular oxygen

Quenching by molecular oxygen of excited states of water-soluble anionic 5,10,15,20-tetarkis-(4-sulfonatophenyl)-porphyrin (H₂TSPP) and cationic 5,10,15,20-tetrakis-(4-N-methylpyridyl)-porphyrin (H₂TMPyP) in aqueous ethanol was investigated. It was found that fluorescence quenching of dissociated (in water) and undissociated (in ethanol) forms of H₂TSPP was diffusion-controlled and occurred at distances close to contact ones (0.5–0.8 nm). Fluorescence of the dissociated form of H₂TSPP was quenched with rate constant k_S that was 1.7 times greater than that of the undissociated form. It was proposed that this was due to a decrease in the porphyrin molecule oxidation potential on going from the undissociated to the dissociated form. It was shown that the most probable reason for the dramatic increase in the rate constant of the fluorescence quenching of H₂TMPyP in water compared with that of H₂TSPP was the low-lying intramolecular charge-transfer state typical of H₂TMPyP. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 170–176, March–April, 2008.     

Electrochemical oxidation of La2CuO4 thin films grown by molecular beam epitaxy

Thin insulating and c-axis oriented films of La₂CuO₄ are grown using a molecular beam epitaxy technique. Subsequently, these films are oxidized electrochemically using a 1N KOH solution. This approach is used to induce superconductivity, leading to a maximum T_c0 of 31 K,, measured both resistively and inductively. The surface morphology, lattice constants and the resistivity before and after the electrochemical treatment are compared.     

Influence of the molecular structure on the quenching of triplet states of porphyrins by molecular oxygen

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 50, No. 4, pp. 618–623, April, 1989.     

Methyl orbital signatures in 2-amino-1-propanol

Electron density distributions of 2-aminoethanol (2AE) and 2-amino-1-propanol (2AP) are calculated in both the coordinate and the momentum spaces using the B3LYP/TZVP method. Using the dual space analysis, molecular orbital signatures of the methyl substituent in 2AP are identified with respect to 2AE. Relaxations of the geometry and the valence orbital in 2AP are found to be due to the insertion of the methyl group. Five orbitals, not four orbitals, are identified as the methyl signatures. They are orbital 5a in the core shell, orbitals 9a and 10a in the inner valence shell, and orbitals 15a and 16a in the outer valence. In the inner valence shell, the attachment of methyl to 2AE causes a splitting of its orbital 8a into orbitals 9a and 10a of 2AP, whereas in the outer valence shell, the methyl group results in the insertion of an additional orbital pair of 15a and 16a. The frontier molecular orbitals 21a, 20a, and 19a are found to have no significant role in the methylation of 2AE.     

熔石英中过氧缺陷及中性氧空位缺陷的几何结构、电子结构和吸收光谱的准粒子计算

本文使用密度泛函理论研究了熔石英中peroxy linkage(POL)缺陷和中性氧空位(NOV)缺陷的几何结构,电子结构以及光学性质.采用自洽的准粒子GW计算结合求解Bathe-Salpeter方程的多体理论,研究了缺陷引起的电子结构和光学吸收谱的变化.首先研究了无缺陷非晶结构的电子结构与吸收谱,得到的结果与实验值非常接近.对POL的计算表明,其在基态下的局部结构与过氧化氢分子类似.采用多体理论计算得到的吸收谱表明其最低吸收峰位于6.3 eV处.这一结果不支持实验认为的位于3.8 eV处的吸收峰是由POL缺陷导致的说法.对于NOV缺陷,计算表明其基态的Si—Si键长为2.51?而三重态下的值则为3.56?.相应的GW+BSE计算表明中性氧空位缺陷导致了位于7.4 eV处的吸收峰,与实验测量结果一致.     

XPS study of vanadium surface oxidation by oxygen ion bombardment

Oxidation of vanadium metal surfaces at room temperature by low-energy oxygen ion beams is investigated by X-ray photoelectron spectroscopy (XPS). It is observed that ion-beam irradiation of clean V results in formation of thin oxide layer containing vanadium in oxidation states corresponding to VO, V₂O₃, VO₂ and V₂O₅ oxides. The composition of the products of ion-beam oxidation depends markedly on oxygen ion fluence. The results of angle-resolved XPS measurements are consistent with a structure of oxide film with the outermost part enriched in V₂O₅ and VO₂ oxides and with V₂O₃ and VO oxides located in the inner region of the oxide layer.     

X-ray photoelectron spectroscopy study of Pd oxidation by RF discharge in oxygen

The low-temperature oxidation of polycrystalline palladium by RF oxygen plasma was studied via X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Detailed information about the electronic states of palladium and oxygen was obtained based on the XPS curve fitting analysis of Pd3d and Pd3p + O1s lines. The results showed that Pd oxidation by oxygen plasma was different from Pd oxidation in pure O₂ at high temperature. SEM shows well-structured submicron PdO particles result from oxidation in pure O₂, whereas plasma oxidation results in the predominant formation of two-dimensional PdO structures covering the initial crystallites of the Pd foil. Further oxidation to a three-dimensional PdO phase occurs under prolonged treatment with oxygen plasma. The formation of a PdO_x (x > 1) species, characterized by a E_b(Pd3d_5/2) = 338.0–338.2 eV value that is close to the Pd⁴⁺ oxidation state, was also observed. This PdO_x species was found to have low thermal stability (T < 400 K). It is proposed that the PdO_x species can be localized within the boundaries of crystallites.     

Semiexperimental equilibrium molecular structures of the maleimide and phthalimide

ABSTRACT

Semiexperimental (SE) equilibrium molecular structures of the title compounds are determined using rotational and ab initio data. Cubic force constants for the parent molecules and a number of isotopologues are calculated at the B2PLYP double hybrid functional with the correlation-consistent triple-ζ cc-pVTZ basis set. Rovibrational and electronic corrections necessary for the transformation of observed ground-state rotational constants to equilibrium ones are calculated using cubic force constants and rotational g tensors. The SE structure parameters are compared with those obtained with CCSD(T) method and basis set of quadruple-ζ quality.

Abbreviations: MP2: Møller–Plesset perturbation theory; CCSD(T): coupled-cluster theory including single and double excitations augmented by a perturbational estimate of the effects of connected triple excitations; VnZ: cc-pVnZ, Dunning's correlation-consistent basis, where n?=?T or Q; CVnZ: cc-pCVnZ, Dunning's correlation-consistent basis, where n?=?T or Q; wCVnZ: cc-pwCVnZ, Dunning's correlation-consistent basis, where n?=?T or Q; AwCVQZ: aug-cc-pwCVQZ, Dunning's correlation-consistent basis; AE: all-electrons; FC: frozen core; QM: quantum mechanics; MAD: mean absolute deviation; SE: semiexperimental equilibrium structure; BO: best ab initio Born–Oppenheimer composite structure; HOMA: harmonic oscillator model of aromaticity; ICSS: iso-chemical shielding surface (isosurface of magnetic shielding value or isosurface of NICS with inverted sign); ICSSZZ: component of magnetic shielding tensor perpendicular to molecular plane; NICS: nuclear independent chemical shift; AIM: atoms in molecules method; ACID: anisotropy of current induced density