Ab initio study of H2SO4 rotamers

This work uses ab initio calculations to obtain harmonic frequencies and anharmonic constants for the O–H symmetric and asymmetric stretches of H₂SO₄ in its C₂, C_s, C_1a, and C_1b configurations. In addition, a high-resolution potential energy surface is calculated as a function of both O=S–O–H dihedral angles in order to accurately obtain minimum and saddle point energies. The resulting peak positions and Boltzmann populations are compared to experimental frequencies and intensities and provide evidence for the assignment of rotamers in H₂SO₄ as suggested in recent work.     

An ab initio study of the potential surface for the reaction H2COH → HCO + H2

The potential surface for the reaction H₂CO⁺H → HCO⁺ + H₂ has been studied by ab initio SCF calculations, using gaussian-type basis functions. A saddle point on the surface has been found, and a reaction path is proposed to explain the observed release of kinetic energy. The energy of activation and ΔE for the reaction have been estimated.     

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.     

丙炴醇聚合膜对铁在酸性溶液中的缓蚀作用

The formation of polymer film of propargyl alcohol(PA) and its protective ability against corrosion in Fe/H_2SO_4 and Fe/H_2SO_4+H_2S systems have been investigated using impedance measurement. The composition and morphology of the corrosion surface of iron, on which PA polymerized at different bines, were obtained with the aid of SEM and AFM as well as EDX. The results showed that PA polymerized into compact polymer film in Fe/H_2SO_4 and Fe/ H_2SO_4 + H_2S systems, which made iron surface smooth and have a morphologies of regular square structure in microscopic level. In Fe/H_2SO_4 system, macroscopic continuous polymer film of PA was not formed leading to local corrosion on electrode surface. In Fe/H_2SO_4 +H_2S system, the adsorption of H_2S and HS - on electrode surface slowed down the formation of polymer film of PA. However, the iron sulfide, produced after a longer time, increased the continuity of the polymer film of PA and therefore, the polymer film could perform its long-te...更多rm inhibition action.     

Carbon nitride formation in gas-phase reactions of CH4, NH3 and H2: an ab initio study

Ab initio QCISD(T)/6-311++(2d,2p) calculations have been carried out for an extensive study of gas-phase reactions among CH₄, NH₃ and their radicals. Our study shows that stable HCN molecules are readily formed by successive H abstraction reactions. Some of the reactions are strongly exothermic and have negligible energy barriers. In agreement with some recent experiments, our results indicate that H abstraction reactions, which make the chemical vapor deposition of diamond thin films successful, do not favor the formation of carbon nitride thin films.     

Ab initio study of the O4 molecule

SCF-CI calculations were done on tetratomic oxygen complexes at various geometries. The results point to the existence of a metastable covalent molecule O₄ completely different from the van der Waals structure (O₂)₂ detected experimentally. At its equilibrium geometry, the O₄ molecule is a quasi-square (r(OO) ≈ 1.4 Å), slightly twisted out of plane, corresponding to the symmetry group D_2d. The activation energy of the reaction O₄(¹A_g) → 20₂(X ³Σ^?_g) is found to be ≈ 15 kcal/mole, that of the inverse reaction, ≈ 75 kcal/mole.     

Al2F2分子结构与稳定性的ab initio计算研究

用abinitio方法在UMP2/6-311G(d)水平下计算了Al2F2分子可能的异构体构型和AlF二聚化成Al2F2分子的反应能。UMP2/6-311G(d)和UQCISD(T)/6-311+G(3df)//UMP2/6-311G(d)水平下的能量值均说明具有D2h对称性、1^Ag电子态的异构是Al2F2分子的最稳定构型,其Al-F键长为0.19074nm,键角Al-F-Al和F-Al-F分别为104.62°和75.38°,以及两个强振动,441.27cm^-1和401.93cm^-1,均与实验结果相符合。电子结构分析表明,具有D2h对称性的异构体的活性中心在2个Al原子上,在形成衍生物时是主要的反应加成位置。在UMP2/6-311G(d)和UQCISD(T)6-311+G(3df)//UMP2/6-311G(d)水平下得到了AlF二聚化能量分别为-75.01kJ/mol和-66.07kJ/mol,与文献估计算基本一致,说明AlF二聚化反应能量上是有利的。     

A study of the reaction Na2SO4·10H2O→Na2SO4+10H2O in the temperature range 0 to 25°C

Thermogravimetry was used to obtain data on the isothermal rate of dehydration and hydration of the reaction Na₂SO₄·10H₂O→Na₂SO₄+10H₂O in the temperature range 10 to 25°C. The thermodynamic functions, ΔH, ΔG and ΔS were calculated and compared with data in the literature. The dissociation pressures of Na₂SO₄·10H₂O at temperatures in the range 0 to 25°C were measured in a volumetric dissociation apparatus. The results obtained were compared with those using thermogravimetry and the accuracy of the two techniques was assessed.     

An ab initio SCF study of conformational isomerism in HNO2

The structures and complete force fields of cis and trans nitrous acid have been calculated with a (7, 3) basis set. The differences between the two stable isomers are reproduced well. The dipole moments, centrifugal distortion constants, vibrational frequencies and isotope shifts also agree satisfactorily with observed values. The fully optimized structures of rotamers corresponding to intermediate values of internal rotation around the N-O bond have been calculated to investigate structural changes during internal rotation. The considerable changes show the strong influence of π electron delocalization in the planar forms. The barrier is calculated to be 8.7 kcal mol⁻¹ in reasonable agreement with experimental values. Both the cis and trans barriers are calculated to be attractive dominant in contradiction to earlier work.     

An ab initio study of the CO–N2 complex

The interaction energy and van der Waals intermolecule bond length of several structures of the CO–N₂ complex are calculated by the supermolecule CCSD(T) and MP4 methods using aug-cc-pVXZ (X=D,T,Q) basis sets extended by a set of midbond functions centered in the middle of the vdW bond. The most stable structures are found to be two distorted T-shaped configurations with the N atom pointing towards the C–O bond. This conclusion is compatible with the results of high-resolution infrared, microwave and millimeter studies.     

Electrochemical behaviour of iron in H2SO4 containing thiophene

The effect of thiophene on the corrosion of iron in H₂SO₄ has been studied by double-layer capacity and polarisation measurements. No change in mechanism was observed by the addition of thiophene, but a significant decrease in the rate of hydrogen evolution was observed. The inhibitor concentration was found to have a significant influence on the behaviour of the open-circuit capacitance, while the change in potential was small. The results show that thiophene is adsorbed on the iron surface according to the Temkin isotherm. The inhibitor efficiencies, as determined from current-voltage curves and the weight loss method, were consistent.     

Kinetics of Mn2O3 digestion in H2SO4 solutions

The kinetics of Mn₂O₃ digestion in various H₂SO₄ solutions (0.5-2.0 M) and at various temperatures (ambient to 80 °C) to form solid γ-MnO₂ and soluble Mn(II) have been examined using X-ray diffraction. Using a modified first-order Avrami expression to describe digestion kinetics, rate constants in the range 0.02-0.98 h⁻¹ were found for Mn₂O₃ disappearance, and 0.03-0.42 h⁻¹ for γ-MnO₂ formation, with higher H₂SO₄ concentrations and temperatures leading to faster conversion rates. Also, for a particular set of experimental conditions, the rate of γ-MnO₂ formation was always slower than Mn₂O₃ disappearance. This was interpreted in terms of the solubility and stability of the soluble Mn(III) intermediated formed during the digestion. Activation energies for Mn₂O₃ dissolution and γ-MnO₂ formation were also determined.     

XPS spectroscopic study of potentiostatic and galvanostatic oxidation of Pt electrodes in H2SO4 and HClO4

The surface oxides produced from potentiostatic and galvanostatic oxidation of Pt electrodes in HClO₄ and H₂SO₄ are examined using X-ray photoelectron spectroscopy. The oxide I species produced as the initial oxidation product by successively more anodic potentiostatic oxidation in 0.2 M HClO₄ is found to have a Pt²⁺ oxidation state, a binding energy characteristic of neither PtO, Pt(OH)₂ or PtO₂, and a limiting thickness of 8 Å. Galvanostatic oxidation in HClO₄ and H₂SO₄ is found to produce PtO₂·H₂O as an unlimiting growth oxide or a limiting growth oxide layer depending on the concentration of the acid electrolyte. The incorporation of the acid electrolyte anion in the surface layer is shown to have an effect on which type of oxide layer is produced. X-ray decomposition and chemical modification by Ar⁺ stripping are shown to produce chemical artifacts complicating any interpretation of a Pt oxide surface layer.     

Anion-ligand interactions: ab initio study of the binding of H2O,CO2 and SO2 to the nitrite ion

Binding enthalpies of single attachment of H₂O, CO₂ and SO₂ to NO^?₂ in the gas phase are reproduced with striking accuracy by SCF ab initio computations using a minimal basis set with counterpoise correction. The positions of binding to NO^?₂ are predicted. The charge-transfer character of the binding, small for water, is slightly increased for CO₂ and appreciable for SO₂.     

Some ab initio valence bond studies of the H5 anion

The results of some ab initio valence bond calculations with 1s basis sets are reported for the anion H⁻₅ as H₂H⁻H₂. Both single-zeta and double-zeta calculations have been performed, with attention given primarily to the results of the single-zeta calculations. For the latter calculations, it is shown that both polarization of the H₂ bonds, and charge transfer from the H⁻ to the H₂ contribute to the binding of the linear anion. In order that bending may occur, it is necessary in these calculations to include a 1s midbond function, whose exponent is the same as that for the 1s atomic orbital of the H⁻. The midbond function is located midway between the hydrogen atoms that are adjacent to the H⁻. With a single-zeta basis, the calculated bond angle is 165°.     

An ab initio study of possible pathways in the thermal decomposition of NaAlH4

Density functional theory (DFT) has been used to study the structural stability of possible intermediate alanate structures, Na₅Al₃H₁₄ and Na₂AlH₅, in the thermal decomposition of NaAlH₄. Na₅Al₃H₁₄ crystallizes in the space group P4/mnc with lattice constants , and c/a=1.52. It is shown that both Na₅Al₃H₁₄ and Na₂AlH₅ have the right thermodynamics and can fit in as an intermediate state during the thermal decomposition process of NaAlH₄. The heat of formation of Na₅Al₃H₁₄ is −60 kJ/mol H₂, which is intermediate between that of NaAlH₄ (−51 kJ/mol H₂) and Na₃AlH₆ (−69.7 kJ/mol H₂). An alternative decomposition pathway based on Na₂AlH₅ has also been discussed. Frequency analysis showed that the least energetic Na₂AlH₅ structure has imaginary frequencies, implying that it is unstable. The presence of soft phonon modes also shows that Na₅Al₃H₁₄ is mechanically metastable. These results are consistent with the notion that they are the intermediate states that lead to the formation of AlH₃. This facilitates the mass transport of aluminum atoms in the decomposition pathway of NaAlH₄.     

Fine structure in Rydberg states of the H2 molecule

The electron spin—nuclear rotation interaction is considered for the np ³Π_u Rydberg series of the H₂ molecule for which much experimental data is available. Earlier formulations of this interaction are reconciled and consistent formulae for both the heteronuclear and homonuclear case are presented. Theoretical calculations of various contributions are given and compared to experimental results. Excellent agreement between calculated and experimental values is obtained for the np Rydberg series of H₂ including H₂⁺.     

XPS- und AES-Untersuchungen an Eisen-Kupfer-Legierungen nach kathodischer Polarisation in H2SO4/H2S

Ohne Zusammenfassung

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XPS- and AES-studies of iron-copper alloys after cathodic polarization in H₂SO₄/H₂S

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Eine ausführliche Veröffentlichung unter stärkerer Berücksichtigung der elektrochemischen Untersuchungen findet sich in Corrosion Science (1984) 24:591–611: C. Kato, H. J. Grabke, B. Egert und G. Panzner, Electrochemical and Surface Analytical Studies on Hydrogen Permeation with Fe-Cu Alloys in Sulfuric acid with and without H₂S.