AlHn(n=1—3)的分子结构和AlH3热力学稳定性

在gaussian03基础上，分别用b3lyp和qcisd方法，在6-311++g^**基组水平上研究了AlH_n(n=1—3)分子及其一价阴阳离子的几何结构和谐振频率，计算了它们中性分子的离解能，第一垂直电离能，电子亲和能. 并与可能得到的实验值及文献上的理论计算值进行了比较. 发现qcisd方法得到的数据更接近实验值. 计算发现对AlH，AlH₂和AlH₃分子及其1价阳离子的Al—H键长，随着H原子数的增多，键长越短， 关键词： 3分子')" href="#">AlH₃分子 平衡几何结构 垂直电离能 垂直电子亲和能     

Ti原子在Al(110)表面吸氢过程中催化作用的第一性原理研究

运用第一性原理方法对H₂分子在Ti掺杂和纯的Al(110)表面的吸附情况进行了研究,发现有Ti原子掺杂时,存在一个H₂分子的吸附路径,即位于Al(110)面顶位Ti原子上方的H₂分子会发生解离,并与Ti原子形成TiH₂分子,然后TiH₂分子向能量更低的空位移动并接近Al(110)表面.态密度与电荷布居分析显示,吸附完成后H原子与表面Al原子存在较强的共价键作用,这为Al-H类物质及Na_{3 关键词： 钛 吸附 解离能 第一性原理}     

CO-H2-O2 reaction on a catalytic surface: A computer simulation study

The oxidation of carbon monoxide to form carbon dioxide and the oxidation of hydrogen to form water are the reactions of environmental and industrial importance. These two reactions have been studied independently by Monte Carlo computer simulation using Langmuir-Hinshelwood mechanism but no effort has been made to study the combined CO-H₂-O₂ reaction on these lines. Keeping in view the importance of this 3-component system, the surface coverages and production rates are studied as a function of CO partial pressure for different ratios of H₂ and O₂. The diffusion of reacting species on the surface as well as their desorption from the surface is also introduced to include temperature effects. The phase diagrams of the system are drawn to observe the behavior of these atoms/molecules on the surface and the production of CO₂ and H₂O are determined at different concentrations of H₂. The results are compared with 2-component systems.     

NaAlH4 表面Ti催化空间构型和X射线吸收光谱: Car-Parrinello分子动力学和密度泛函理论研究

通过采用Car-Parrinello分子动力学方法对掺杂Ti前后的NaAlH₄(001)2×2×1超晶胞表面晶体在333 K(60 ℃)温度条件催化脱氢的空间构型做了理论研究,发现掺杂Ti的合金中AlH₄团的其中两个Al—H键长分别从约1.64 (1 =0.1 nm)增大至1.74和1.93 ,而未掺杂合金表面中AlH₄团的4个Al—H键长基本不变,这意味着掺杂Ti相对未掺杂的合金更易于放氢.但在模拟温度条件下并未发现Ti-Al成键趋     

A Refinement of the InF3.3H2 O Structure by the Use of NMR Data

Bokij and Khodashova' derived from X-ray diffraction study and coordination considerations that InF.3H₂O is pseudotetragonal with a=7.90, c=4.14 8, 2=2, space group PII2/n. each indium atom is surrounded by six ligands (F and H₂O) to form nearly are gular octahedron. The adjacent octahedra have common a pices forming in finitechains along the c-axis. Since the F and O scattering factors are much the same, the identification of F atoms and H₂O molecules was performed on the basis of coordination considerations. The bridges between In atoms were unambiguously identif iedas fluorine atoms (F). The fouro the rligands of each octahedron are two fluorine atoms (F) and two water molecules (H₂O equatorial plane of the octahedra (fluorines under fluorines in order to retain 2=2). estimated as oxygens of H₂O_I molecules due to the irspecifictetrahedral surrounding by F_II and H₂O_I In such a lamellar structure, the layers of H₂O_I and H₂O_II molecules interchange with the layers of F atoms. The existence of H₂O layersin the InF₃.3H₂structure, claimed by B. and K., is notin agreement with the factth that the crystals of this fluoride have needle-like habitus and do not exhibit excellent cleavage in the plane (110). In order toresolve this contradiction and find out the proton position sin the InF.3H ₂o structure, we have applied the NMR method     

氧化石墨烯负载的Pt单原子催化硼胺烷水解机理的理论研究

本文研究了氧化石墨烯负载Pt单原子(Pt₁/Gr-O)催化硼胺烷(NH₃BH₃)全水解反应机理,即一分子的NH₃BH₃生成三分子的氢气(H₂)的过程. 在水解路径中,首先吸附的硼胺烷连续断裂两个B-H键生成第一分子的H₂. 接着,一个H₂O分子与^*BHNH₃基团(^*表示吸附态)反应生成^*BH(H₂O)NH₃,其中伸长的O-H键断裂后形成^*BH(OH)NH₃. 然后,第二个H₂O与^*BH(OH)NH₃反应生成^*BH(OH)(H₂O)NH₃,在指向Pt₁/Gr-O表面的O-H断裂后,生成BH(OH)₂NH₃并脱附到水溶液中. 两个水分子脱氢产生的两个H原子脱附生成第二个H₂分子,且Pt₁/Gr-O催化剂恢复. 脱附后的BH(OH)₂NH₃在水溶液中水解生成第三个H₂分子. 纵观整个水解反应,H₂O分子和^*BHNH₃基团的结合是反应速控步,其反应能垒是16.1 kcal/mol. 因此,Pt₁/Gr-O有希望成为室温催化NH₃BH₃全水解催化剂.     

H2O adsorption on Ni(100): Evidence for oriented water dimers

H₂O adsorption on clean Ni(110) surfaces at T ≦ 150 K leads at coverages below $\text{θ ? 0.5}$ to the formation of chemisorbed water dimers, bound to the Ni substrate via both oxygen atoms. The linear hydrogen bond axis is oriented parallel to the [001] surface directions. With increasing H₂O coverage $\text{(θ ≧ 0.5)}$, the accumulation of further hydrogen bonded water molecules induces some modification of the dimer configuration, producing at $\text{θ ? 1}$ a two-dimensional hydrogen bonded network with a slightly distorted ice lattice structure and long range order.     

Water enrichment by hydroxyl and hydrogen peroxide due to cavitation treatment: GHz four-wave mixing spectroscopy

Four-waves mixing spectroscopy has been applied to detection of H₂O₂ and OH molecules in water after different treatments in a cavitation jet. The considerable growth of the ortho-H₂O, OH, and H₂O₂ rotational lines amplitude in cavitation water relatively to distilled water and 1% hydrogen peroxide aqueous solution have been found. This fact was interpreted as the exhibition of H₂O molecules dissociation onto atoms and recombination into OH and H₂O₂. Four-waves mixing spectra fitting gives the evaluation of H₂O₂ rotational line’s amplitude increasing in cavitation water by factor of ～3 in comparison to 1% H₂O₂ aqueous solution.     

Vibrational Spectra and Structure of Potassium Alum Kal(SO4)2·12[(H2O) x (D2O)1−x ]

The IR spectra and polarization Raman spectra of Kal(SO₄)₂·12(H₂O) and Kal(SO₄)₂·12[H₂O)_0.3(D₂O)_0.7] crystals at 93 K and room temperature have been obtained experimentally. The vibrational spectra of structural elements of potassium alum — the complexes [Al(H₂O)₆ ³⁺ and [Al(D₂O)₆]³⁺ — have been calculated. The vibrational spectra have been interpreted based on the calculation and factor-group analysis data. The spectral data obtained point to the fact that, in the crystals considered, the sulfate ions are partially disordered and there exist two crystallographically different types of water molecules.     

Collective defect formation in the high-temperature superconductor YBa2Cu3O7 under the influence of adsorbed water molecules

The mechanisms for defect formation stimulated by the adsorption of water molecules in the surface of YBa₂Cu₃O₇ ceramic are studied, together with the types of defects and their distributions. It is found that a water layer physically bound to the surface reduces the rates of annihilation and capture of positrons, changes the amount of barium and copper on the surface by a factor of two, and inhibits diffusive jumps of nickel atoms. A layer of adsorbed water excites subthreshold formation of 10²¹ cm⁻³ interstitial Ba and Cu1 atoms and transitions of oxygen from O1 to O5, and vice versa in the volume of crystallites, and the migration of defects and accumulation of Ba atoms in the surface layer, which block diffusive jumps of Ni within the volume of the crystals. These effects are related to the excitation of collective, low-frequency weakly damped motion of heavy holes in the crystal volume when defects are formed on the surface by physically adsorbed H₂O molecules, which is accompanied by Coulomb repulsion of cations from intermediate layers into interstitials and the migration of defects in the field of the collective excitations. Zh. éksp. Teor. Fiz. 116, 586–603 (August 1999)     

The use of direct recoil spectrometry (DRS) for the study of water vapor interactions on polycrystalline metallic surfaces—the H2O/U and H2O/Ti systems

Using direct recoil spectrometry (DRS), the shadowing of surface H atoms by neighboring O atoms can differentiate between full and partial dissociation routes of water molecules on the surface as well as point to the geometrical arrangements of hydroxyl surface groups. The H₂O/U and H₂O/Ti systems were compared. It has been found that different mechanisms control the water-surface interactions in these systems.For the H₂O/U system, a simple direct-collision (Langmuir-type) dissociative chemisorption controls the process. Two consecutive stages were identified: (i) below ∼70% monolayer coverage, a complete dissociation of water into oxygen ion and two H atoms, which chemisorb on the remaining unreacted metallic surface and (ii) above about 70% of a full layer coverage, three dimensional oxide islands start to form, causing partial dissociation of water and the formation of surface hydroxyls.For the H₂O/Ti system, a more complicated mechanism, which involves a precursor state, seems to control the process. In that case, two concurrent routes act simultaneously. In addition to the simple direct-collision mechanism, water precursor clusters (bound by hydrogen bonds), which partly dissociate, result in chemisorbed tilted hydroxyl clusters (even at low-coverage). The relative contributions of the precursor route and the direct-collision route are pressure dependent, with the former being dominant at higher exposure pressures.     

Accelerated thermal decomposition of AlH3 for hydrogen-fueled vehicles

The potential for using aluminum hydride, AlH₃, for vehicular hydrogen storage is explored. It is shown that particle-size control and doping of AlH₃ with small levels of alkali-metal hydrides (e.g. LiH) results in accelerated desorption rates. For AlH₃–20 mol% LiH, 100 °C desorption kinetics are nearly high enough to supply vehicles. It is highly likely that 2010 gravimetric and volumetric vehicular system targets (6 wt% H₂ and 0.045 kg/L) can be met with onboard AlH₃. However, a new, low-cost method of off-board regeneration of spent Al back to AlH₃ is needed. PACS 68.43.Vx; 68.43.Mn; 83.80.Fg; 84.60.Ve; 51.30.+i; 61.10.Nz     

Zr催化剂对NaAlH4和Na3AlH6可逆储氢性能的影响

采用基于密度泛函理论的平面波赝势方法,分别计算纯净的以及掺杂Zr的NaAlH₄和Na₃AlH₆的晶格结构常数、能量、电子局域函数和电子态密度.结果表明：NaAlH₄和Na₃AlH₆分别是带隙为46和31 eV的绝缘体;NaAlH₄和Na₃AlH₆中Al—H键是共价键,Na—H键是离子键;Zr原子替代Na原子 关键词： 储氢 4')" href="#">NaAlH₄ 3AlH₆')" href="#">Na₃AlH₆ Zr掺杂     

Oxidation of Al single crystal surfaces by exposure to O2 and H2O

The initial stages of oxidation of Al single crystals are studied by soft X-ray photoemission spectroscopy at photon energies hv = 30 eV and 111.13 eV using synchroton radiation. Both the valence band region and the substrate Al 2p core levels are measured with high resolution to clarify the differences between (a) the geometrical effects at different surfaces, (100) and (110), and (b) between the oxidation by pure O₂ and H₂O. There is a well established but not very dramatic differences in the O 2p induced band between the two crystal surfaces when oxidizing with O₂. The Al 2p spectra reveal an initial state of oxidation with less O atoms per Al atom than in Al₂O₃ate disappears at higher exposures with O₂ while it is absent when oxidizing with H₂O. Only about 1/4 of the exposure with H₂O is needed to obtain the same coverage as with O₂.     

Transport properties of carbon atomic wire in the environment of H2O molecules: An ab initio study

The transport properties of carbon atomic wire in the environment of H₂O molecules are studied by the non-equilibrium Green function method based on density functional theory. In particular, the carbon wire with seven atoms sandwiched between the Al(1 0 0) electrodes is considered. It is found that the transport properties are sensitive to the variation of the number and the position of the H₂O molecule adsorbed on the carbon wire. To our surprise, with different positions of a single H₂O molecule on the carbon wire, the equilibrium conductance shows an evident odd–even oscillatory behavior. For example, the equilibrium conductance of the carbon wire becomes bigger when the H₂O is adsorbed on the odd-numbered carbon atoms; an opposite conclusion is obtained for the H₂O adsorbed on the even-numbered carbon atoms. For the cases of two H₂O molecules, the equilibrium conductance varies largely and the contribution of the third eigenchannel becomes larger in some special configurations. The calculated current–voltage curves show different behavior with the variation of the positions of the H₂O molecules. In certain cases, large negative differential resistance (NDR) is shown, while in other cases, it only slightly deviates from the linear behavior. The above behavior is analyzed via the charge transfer and the density of states (DOS) and reasonable explanations are presented.     

Structural characterization of nanocrystalline CrOOH·2H2O aerogel by X-ray diffraction

The nanostructured powder prepared by critical CO₂ extraction of the urea-assisted wet chromia gel mixture at 373 K in vacuum was studied by X-ray diffraction techniques. Thermoanalytical methods showed the presence of the lattice water molecules in the resulting phase corresponding to a chemical formula CrOOH·2H₂O. The CrOOH·2H₂O nanocrystals of 3-5 nm in diameter were observed in transmission electron microscopy and their structure was derived from the Rietveld analysis in which the disorder contribution to the X-ray scattering was implemented. The structural model shows that the hexagonal unit cell of α-CrOOH undergoes monoclinic distortion with half of the O⁻² anions and OH⁻ groups being replaced by bonded water molecules in the three-dimensional packing resulting in half of the sites in regular Cr⁺³ octahedra being vacant. Further examination of the quasi-crystalline disordered state of the CrOOH·2(H₂O) nanocrystals was performed by model independent method of Radial Distribution Function (RDF). This complementary technique is sensitive to the molecular composition and allows to assess the average atomic (or electron) density distribution and the spacings of the atomic arrangements in the nearest neighbor shells comprising the range of the crystalline order in the structure of this material.     

Interaction between nanobuds and hydrogen molecules: A first-principles study

Hydrogen storage materials are crucial for the wide application of hydrogen in fuel cells. In this Letter, the interaction between hydrogen molecules and nanobuds has been studied using the Dmol3 package. The results show that the adsorption energies of hydrogen molecules onto nanobuds range from 0.069 eV to 0.115 eV, and that the adsorption energies are not sensitive to the nanobuds' structures but closely related to the number of carbon atoms around H₂ molecules. The energy barrier of a hydrogen molecule entering C176 is 2.38 eV. Each C176 nanobud can accommodate four H₂ molecules. The stress existing in nanobuds induces alterative charge distribution, which can improve the hydrogen storage performance of nanobuds to a certain extent.     

Study on the phase transitions by nuclear magnetic resonance of α-type RbAl(SO4)2·12H2O and β-type CsAl(SO4)2·12H2O single crystals

The thermodynamic properties, spin–lattice relaxation times, T₁, and spin–spin relaxation times, T₂, of the ²⁷Al, ⁸⁷Rb, and ¹³³Cs nuclei in MAl(SO₄)₂·12H₂O (M=Rb and Cs) crystals were investigated, and the two crystals were found to lose H₂O with increases in temperature. From our results for T₁ and T₂, we conclude that the discontinuities near T_d in the T₁ curves of the two crystals correspond to structural changes. In both crystals, below T_d the water molecules surrounding the Al³⁺ and M⁺ nuclei form distorted octahedra, whereas above T_d the water molecules around the Al³⁺ and M⁺ nuclei form regular octahedra and the environment of the Al³⁺ and M⁺ nuclei has cubic symmetry. Further, the T₁ for the ²⁷Al and ⁸⁷Rb nuclei in RbAl(SO₄)₂·12H₂O below T_d were found to increase with increasing temperature, whereas the T₁ for the ²⁷Al and ¹³³Cs nuclei in CsAl(SO₄)₂·12H₂O were found to decrease. It is possible that this difference is due to the different characteristics of α- and β-type crystals.     

Micromechanical and thermal behaviour of gel grown pure- and sodium-modified copper tartrate crystals

Results regarding micromechanical characteristics of gel grown pure- and sodium-modified copper tartrate crystals, bearing composition CuC₄H₄O₆·3H₂O, (Cu)_0.77(Na)_0.23C₄H₄O₆·3H₂O and (Cu)_0.65(Na)_0.35C₄H₄O₆·H₂O, as obtained on using indentation induced hardness testing technique are reported. Thermal behaviour of these crystals in the temperature ranging from room temperature (∼25 °C) to about 600 °C is also reported. Pure copper tartrate crystals are found to be thermally more stable than the sodium-modified ones. Dependence of Vickers’ hardness number H_v on load ranging from 0.049 to 2.94 N on two different planes for all the three compositions is analyzed. It is shown that after initial rise in the value of H_v, the same achieves saturation at a load of 0.49 N. Modification of copper tartrate crystal by introducing sodium in its lattice brings about a change in the micromechanical characteristics. The saturation value of H_v decreases with increase in the concentration of sodium ions. The results on (0 0 1) and (1 1 1) planes for both pure and modified copper tartrate crystals suggest hardness anisotropy. Relative difference of hardness between the two planes and yield strength for both pure and modified copper tartrate crystals is worked out. The experimental results are analyzed for applicability of Meyer’s law and Proportional Specimen Resistance Model. It is suggested that the experimental results indicating reverse ISE phenomenon may be explained in terms of the existence of a distorted zone near the crystal-medium interface. The integral method of Coats and Redfern approximation applied to the thermoanalytical data suggests “Random Nucleation Model” for the reaction kinetics of these crystals. Non-isothermal kinetic parameters such as activation energy, frequency factor and order of reaction are calculated.     

SERS investigation of interfacial water at a silver electrode in acetonitrile solutions

Surface-enhanced Raman scattering from a silver electrode in solution of 0.1 M LiClO₄ in acetonitrile has been analyzed as a function of applied potential. Three ν(O-H) bands associated with the interfacial water and two ν(O-H) bands associated with the OH⁻ ion species were observed depending on the electrode potential. The band at 3487 cm⁻¹ is favored at relatively positive potentials and assigned to H₂O molecules interacting with the electrode surface via the oxygen atoms. Another band at 3586 cm⁻¹ appears in a wider potential region and is assigned to the H₂O molecules with one or both of the hydrogen atoms facing the electrode surface. Additionally, evidence for the possible surface ion pair, Li⁺OH⁻, which is closely associated with H₂O molecules and the quasi-crystalline form of LiOH are also presented in this paper.