VOxH2O (x= 1——-5)团簇的结构及稳定性研究

用密度泛函理论(DFT),在B3LYP/DZP水平上对H₂O分子与VO_x形成的团簇VO_xH₂O (x= 1---5)进行结构优化、能量和频率的计算,研究了团簇的稳定结构、稳定性和频率特性.结果表明VO_xH₂O (x= 1---5) 团簇的基态构型的电子态均为²A, 对称性均属C₁对称点群,其中x= 1, 4, 5时基态构型中水分子已被解离.水分子倾向于吸附在团簇VO_x上, 形成VO_xH₂O (x= 1---5)团簇. VO_xH₂O (x= 1---5)团簇中, VO_xH₂O (x= 1,4,5) 的化学活性小于VO_xH₂O (x= 2, 3)的化学活性.此外, H₂O体系与VO_x之间的结合强弱顺序为 VO₄H₂O > VO₅H₂O > VOH₂O > VO₃H₂O > VO₂H₂O. VOH₂O中离解出H原子的能量为2.88 eV和从VO₅H₂O中离解出OH基团的能量为2.38 eV, 均在可见光能量范围内,这两个化学过程有可能在可见光催化条件下进行.可以通过团簇的红外和拉曼谱特征, 初步判断水分子在VO_xH₂O团簇中是否离解.     

Ions with strong symmetric H-bonds and their solvation in aqueous-ethanolic solutions of HCl

Ion-molecular interactions in the HCl-EtOH-H₂O system are studied by means of multiple frustrated total internal reflection IR spectroscopy over a wide range of concentrations of the components. It is demonstrated that, in the investigated solutions, the acid is fully bound into ions and uncharged complexes formed by strong symmetric or quasi-symmetric H-bonds. There is a competition between H₂O and EtOH molecules during the formation of the (H₅C₂(H)O…H…O(H)C₂H₅)⁺, (H₂O…H…OH₂)⁺, and (H₂O…H…O(H)C₂H₅)⁺ proton disolvates. In dilute solutions of HCl in 2: 1 and 1: 1 EtOH-H₂O mixtures, (H₂O…H…OH₂)⁺ proton dihydrates are mainly formed, whereas in concentrated HCl solutions, under conditions of a partial solvation of ions by solvent molecules, predominantly (H₂O…H…O(H)C₂H₅)⁺ mixed proton disolvates arise. In concentrated solutions of HCl in EtOH with low water content, the acid is partially bound into (H₅C₂(H)O…H⁺…Cl^?) uncharged complexes with the participation of the Cl^? anion.     

Tree species of the central amazon and soil moisture alter stable isotope composition of nitrogen and oxygen in nitrous oxide evolved from soil

The use of stable isotopes of N and O in N₂O has been proposed as a way to better constrain the global budget of atmospheric N₂O and to better understand the relative contributions of the main microbial processes (nitrification and denitrification) responsible for N₂O formation in soil. This study compared the isotopic composition of N₂O emitted from soils under different tree species in the Brazilian Amazon. We also compared the effect of tree species with that of soil moisture, as we expected the latter to be the main factor regulating the proportion of nitrifier- and denitrifier-derived N₂O and, consequently, isotopic signatures of N₂O. Tree species significantly affected δ ¹⁵N in nitrous oxide. However, there was no evidence that the observed variation in δ ¹⁵N in N₂O was determined by varying proportions of nitrifier- vs. denitrifier-derived N₂O. We submit that the large variation in δ ¹⁵N-N₂O is the result of competition between denitrifying and immobilizing microorganisms for NO 3 m . In addition to altering δ ¹⁵N-N₂O, tree species affected net rates of N₂O emission from soil in laboratory incubations. These results suggest that tree species contribute to the large isotopic variation in N₂O observed in a range tropical forest soils. We found that soil water affects both ¹⁵N and ¹⁸O in N₂O, with wetter soils leading to more depleted N₂O in both ¹⁵N and ¹⁸O. This is likely caused by a shift in biological processes for ¹⁵N and possible direct exchange of ¹⁸O between H₂O and N₂O.     

First-principles calculations of the structural,elastic, electronic and optical properties of Si2P2O and Ge2P2O at high pressures

The structures of Si₂P₂O and Ge₂P₂O with the space group Cmc21 are derived. The structural, mechanical, elastic anisotropy, electronic and optoelectronic properties are calculated by first principles calculations based on density functional theory (DFT) with generalized gradient approximation (GGA) at high pressure for Si₂P₂O and Ge₂P₂O. By using the elastic stability criteria, it is shown that their structures are all stable. The phonon dispersion spectra are researched throughout the Brillouin zone as implemented in the CASTEP code, which indicates that the optimized structures are stable dynamically. The brittle/ductile behaviors are assessed in the pressures from 0 GPa to 50 GPa. Our calculations present that the performances of them become ductile with pressure rise. Moreover, the anisotropies of them are discussed by the Young's moduli at different pressure, and the results indicate that the anisotropies of them are obvious. The direct band structures of Ge₂P₂O and the indirect band gap of Si₂P₂O show that Si₂P₂O and Ge₂P₂O present semiconducting character at 0 GPa and 50 GPa. The band structures of Si₂P₂O are changed obviously with the increase of pressure. The total DOS originate mainly from O ‘s’ states, O ‘p’ states, P ‘s’ states and P ‘p’ states and M ‘p’ states (M=Si, Ge). The trends of DOS for Si₂P₂O and Ge₂P₂O display many similarities, and the change of DOS is obviously affected by the pressure for Si₂P₂O. The optoelectronic properties of them are researched. The calculated static dielectric constants, ɛ₁(0), are 3.2 at 0 GPa and 6.4 at 50 GPa for Si₂P₂O, and the values of Ge₂P₂O are 10.2 and 9.2 at 0 GPa and 50 GPa.     

Adsorption behavior of H2O on clean and oxygen precovered Ni(s)(111)

Photoelectron spectroscopy (UPS), thermal desorption spectroscopy (TDS), isotope exchange experiments, work function change (δφ) and LEED were used to study the adsorption and dissociation behavior of H₂O on a clean and oxygen precovered stepped Ni(s)[12(111) × (111)] surface. On the clean Ni(111) terraces fractional monolayers of H₂O are adsorbed weakly in a single adsorption state with a desorption peak temperature of 180 K, just above that of the ice multilayer desorption peak (T_m = 155 K). In the angular resolved UPS spectra three H₂O induced emission maxima at 6.2, 8.5 and 12.3 eV below E_F were found for θ ≈ 0.5. Angular and polarization dependent UPS measurements show that the C_2v symmetry of the H₂O gas-phase molecule is not conserved for H₂O(ad) on Ni(s)(111). Although the Δφ suggest a bonding of H₂O to Ni via the negative end of the H₂O dipole, the O atom, no hints for a preferred orientation of the H₂O molecular axes were found in the UPS, neither for the existence of water dimers nor for a long range ordered H₂O bilayer. These results give evidence that the molecular H₂O axis is more or less inclined with respect to the surface normal with an azimuthally random distribution. H₂O adsorption at step sites of the Ni(s)(111) surface leads in TDS to a desorption maximum at T_m = 225 K; the binding energy of H₂O to Ni is enhanced by about 30% compared to H₂O adsorbed on the terraces. Oxygen precoverage causes a significant increase of the H₂O desorption energy from the Ni(111) terraces by about 50%, suggesting a strong interaction between H₂O and O(ad). Work function measurements for H₂O+O demonstrate an increase of the effective H₂O dipole moment which suggests a reorientation of the H₂O dipole in the presence of O(ad), from inclined to a more perpendicular position. Although TDS and Δφ suggest a significant lateral interaction between H₂O+O(ad), no changes in the molecular binding energies in UPS and no “isotope exchange” between ¹⁸O(ad) and H₂¹⁶O(ad) could be observed. Also, dissociation of H₂O could neither be detected on the oxygen precovered Ni(s)(111) nor on the clean terraces.     

Electronic energy transfer between dye molecules in structured solutions of H<Subscript>2</Subscript>O and D<Subscript>2</Subscript>O

The structure of H₂O+D₂O solutions was studied by correlation spectroscopy of scattered light. The correlation function and size of scatterers were both found to depend nonmonotonically on the D₂O concentration in the H₂O+D₂O mixture. Processes of transfer of electronic excitation energy between dye molecules of different types in H₂O+D₂O solutions were studied. The efficiency of these processes was found to depend extremally on the concentration of the components of the solution. A fractal distribution of the interacting dye molecules is ascertained from the experimental data. The dependence of the fractal dimensionality of the dye solutions on the D₂O concentration in the D₂O+H₂O mixture is determined.     

An isotopic labeling study of the diffusion mechanism during oxidation of Si(100) in water vapor by successive oxidation

The diffusion mechanism during the wet oxidation of Si(100) at 1373 K was investigated by successive oxidations finally containing isotopic water. SiO₂ was first thermally grown on Si in non-labeled oxidizing ambient (dry O₂ or H₂O) followed by isotopic water (H₂¹⁸O) to trace ¹⁸O species in SiO₂. The distributions of ¹⁶O and ¹⁸O in the oxide film were analyzed by means of secondary ion mass spectroscopy (SIMS). SIMS depth profiles show that there was a wide overlap of both isotopes (¹⁸O and ¹⁶O) throughout the SiO₂ layer, no matter whether the first oxidation step was carried out in dry O₂ or H₂O, and the concentration gradient of ¹⁸O decreased with increasing oxidation time at the second oxidation step by H₂¹⁸O. The results suggest that the diffusion mechanism in SiO₂ during water vapor oxidation is exchange diffusion; H₂O related oxidizing species diffuse through the network with significant exchange with the pre-existing oxygen in it.     

IR-Spectra of M2UO2F4.H2O Complexes

This work is devoted to the study of and Rb₂UO₂F₄.H₂O and Cs₂UO₂F₄. H₂O IR-spectra with the aim of obtaining a set of vibration frequencies characterising M₂U0₂F₄.H₂O complexe elucidating the role and nature of water bonds in the structures of the above-mentioned compounds; and receiving preliminary information on the structure of M₂UO₂F₄.H₂O. The investigated compounds were synthesized in accord with our previous paper¹. M₂UO₂D₂O and M₂UO₂F₄.HDO were obtained by recrystallizing M₂UO₂F₄.H₂O from D₂O and HDO respectively     

Effect of a single water molecule on the formations of H2O2 + ClO from HO2 + HOCl reaction under tropospheric conditions

ABSTRACT

In this work, four different channels, represented by H₂O???HO₂ + HOCl, HO₂???H₂O + HOCl, H₂O???HOCl + HO₂ and HOCl???H₂O + HO₂ have been analysed for water-catalysed formations of H₂O₂ + ClO to gain insight into the potential impact of the reaction in the atmosphere. The results at the CCSD(T)/aug-cc-pVTZ//MP2/6-311+G(2df,2p) level show that the H₂O???HO₂ + HOCl reaction is kinetically the most favourable channel among the four channels. Compared to the channel of H₂O₂ + ClO formations without water vapour, the effective rate constant of H₂O???HO₂ + HOCl reaction is estimated to be faster than the naked reaction by 2–3 orders of magnitude, indicating that the single water molecule in the H₂O???HO₂ + HOCl channel exhibits a positive catalytic effect on enhancing the rate of H₂O₂ + ClO formations. Meanwhile, it is interesting that the transfer process between H₂O???HOCl + HO₂ and H₂O???HO₂ + HOCl has an activation energy of 0.6 kcal?mol^?1 and can occur easily under tropospheric conditions.     

Catalytic effect of water,water dimer,water trimer,HCOOH, H2SO4, CH3CH2COOH and HN(NO2)2 on the isomerisation of HN(NO2)2 to O2NNN(O)OH: a mechanism study

In this article, the isomerisation mechanisms of HN(NO₂)₂ to O₂NNN(O)OH without and with catalyst X (X = H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄, CH₃CH₂COOH and HN(NO₂)₂) have been investigated theoretically at the CBS-QB3 level of theory. Our results show that the catalyst X (X = H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄ and CH₃CH₂COOH) shows different positive catalytic effects on reducing the apparent activation energy of the isomerisation reaction processes. Such different catalytic effects are mainly related to the number of hydrogen bonds and the size of the ring structure in X (X = H₂O, (H₂O)₂ and (H₂O)₃)-assisted transition states, as well as different values of pK_a for H₂SO₄, HCOOH and CH₃CH₂COOH. Very interesting is also the fact that H₂SO₄-assisted reaction is the most favourable for the hydrogen transfer from HN(NO₂)₂ to O₂NNN(O)OH, due to the smallest pK_a (?3.0) value of H₂SO₄ than H₂O, HCOOH, H₂SO₄ and CH₃CH₂COOH, and also because of the largest ∠X???H???Y (the angle between the hydrogen bond donor and acceptor) involved in H₂SO₄-assisted transition state. Compared to the self-catalysis of the isomerisation mechanisms of HN(NO₂)₂ to O₂NNN(O)OH, the apparent activation energy of H₂SO₄-assisted channel also reduces by 9.6 kcal?mol^?1, indicating that H₂SO₄ can affect the isomerisation of HN(NO₂)₂ to O₂NNN(O)OH, most obvious among all the catalysts H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄, CH₃CH₂COOH and HN(NO₂)₂.     

Coordination and solvation of noble metal ions: Infrared spectroscopy of Ag+(H2O)n

Vibrational spectra of mass-selected Ag⁺(H₂O)_n ions are measured by infrared photodissociation spectroscopy and analyzed with the aid of density functional theory calculations. Hydrogen bonding between H₂O molecules is found to be absent for cold Ag⁺(H₂O)₃, but detected for Ag⁺(H₂O)₄ through characteristic changes in the position and intensity of OH-stretching transitions. The third H₂O coordinates directly to Ag⁺, but the fourth H₂O prefers solvation through hydrogen bonding. The preference of the tri-coordinated form is attributed to the inefficient 5s–4d hybridization in Ag⁺, in contrast to the efficient 4s–3d hybridization in Cu⁺. For Ag⁺(H₂O)₄, however, di-coordinated isomers are identified in addition to the tri-coordinated one.     

Photocatalytic performance of Cu2O and Ag/Cu2O composite octahedra prepared by a propanetriol-reduced process

Cu₂O and Ag/Cu₂O composite octahedra were synthesized via a hydrothermal reaction of CuAc₂ with urea in H₂O–propanetriol binary solution by adjusting the quantity of AgNO₃ at 180 °C for 10 h. The influence of reaction temperature and time on the morphology and phase of the products was investigated, and a possible growth mechanism of Cu₂O octahedron was also proposed. The photocatalytic activities of the as-prepared Cu₂O and Ag/Cu₂O octahedra for the degradation of methyl orange aqueous solution were studied. The results show that they are effective photocatalysts for the degradation of methyl orange, and the photocatalytic ability of Ag/Cu₂O composite is stronger than that of Cu₂O octahedra, which are expected to be useful in the treatment of wastewaters.     

A first principle study on the magnetic properties of Cu2O surfaces

Spin-polarized density functional theory calculations were performed to investigate the magnetism of bulk and Cu₂O surfaces. It is found that bulk Cu₂O, Cu/O-terminated Cu₂O(111) and (110) surfaces have no magnetic moment, while, the O-terminated Cu₂O(100) and polar O-terminated Cu₂O(111) surfaces have magnetism. For low index surfaces with cation and anion vacancy, we only found that the Cu vacancy on the Cu₂O(110) Cu/O-terminated surface can induce magnetism. For atomic and molecular oxygen adsorption on the low index surfaces, we found that atomic and molecular oxygen adsorption on the Cu-terminated Cu₂O(110) surface is much stronger than on the Cu/O-terminated Cu₂O(111) and Cu-terminated Cu₂O(100) surfaces. More interesting, O and O₂ adsorption on the surface of Cu/O terminated Cu₂O(111) and O₂ adsorption on the Cu-terminated Cu₂O(110) surface can induce weak ferromagnetism. In addition, we analysis origin of Cu₂O surfaces with magnetism from density of state, the surface ferromagnetism possibly due to the increased 2p–3d hybridization of surface Cu and O atoms. This is radically different from other systems previously known to exhibit point defect ferromagnetism, warranting a closer look at the phenomenon.     

Raman spectroscopic study of the hydrogen and arsenate bonding environment in isostructural synthetic arsenates of the variscite group—M3+ AsO4·2H2O (M3+ = Fe,Al, In and Ga): implications for arsenic release in water

The Raman spectra of synthetic compounds equivalent to the variscite group: FeAsO₄·2H₂O AlAsO₄·2H₂O, GaAsO₄·2H₂O, and InAsO₄·2H₂O are reported. In particular, upon comparison of FeAsO₄·2H₂O to AlAsO₄·2H₂O, it is observed that the Type II (weak) H‐bond lengths in the latter are slightly longer, which is postulated to affect the stability (As release) in water at pH 5 and 7. Arsenate stretching and bending vibrations were found to be distinct in terms of spectral structure and therefore well suited for fingerprinting. The calculated As O bond strengths from existing crystallographic data showed no significant variations. The strongest ν₁ (AsO₄³⁻) stretch was used to monitor the As O bonding interactions in the four As O M units, where a shift of 114 cm⁻¹ was observed in the order FeAsO₄·2H₂O (lowest) < InAsO₄·2H₂O < GaAsO₄·2H₂O < AlAsO₄·2H₂O (highest); this order also followed exactly the measured arsenic release of these phases. This shift in ν₁ (AsO₄³⁻) position was rationalized to stem from the differences in the electronegativities of the M³⁺ cations. The trends mentioned above were verified and found to also hold for the isostructural phosphate analogues strengite (FePO₄·2H₂O) and variscite (AlPO₄·2H₂O) using published data. Therefore, it is postulated that, as observed with the stability of solution complexes, there may be a correlation between the electronegativity of the M³⁺ cation in these isostructural phases and their stability (As or P release) in water. Copyright © 2010 John Wiley & Sons, Ltd.     

Penning ionization electron spectroscopy of H2O,D2O,H2S and SO2

Electron energy peak shifts and peak shapes were determined in the ionization of H₂O, D₂O, H₂S and SO₂ by Ne(³P₂) and He(2¹S, 2³S) metastable atoms. The shifts are large, especially in ionization of H₂O and D₂O into the ionic ground state and are probably mostly due to chemical interaction during the collision.In a previous paper the electron energy distribution curves for ionization of CO, HCl, HBr, N₂O, NO₂, CO₂, COS and CS₂ by helium, neon and argon metastables and the characteristics of this ionization were described¹. In this paper the series of triatomic molecules was extended to the molecules H₂O, D₂O, H₂S and SO₂. Because all these molecules have considerable dipole moments it could be expected that the peak shifts might be enhanced as compared with other triatomic molecules.     

The hydrates and deuterates of ferrous sulfate (FeSO4): a Raman spectroscopic study

A comparative analysis has been carried out on the Raman spectra of FeSO₄·nH₂O (n = 1, 4, 7) including the ²D‐analogs. The effects of changing the degrees of hydration have been found from the lattice, SO₄²⁻ internal, and H₂O internal modes. Increasing degrees of hydration shift the intense ν₁(SO₄) peak to lower wavenumbers and reduce the amount of splitting on the ν₃(SO₄) peaks. Some of the water librational bands cause the broadening of the ν₄(SO₄) peaks in FeSO₄·7H₂O and the ν₂(SO₄) peaks in FeSO₄·7D₂O. The ν₂(H₂O) band in FeSO₄·H₂O is red‐shifted in excess of 100 cm⁻¹ relative to the unperturbed H₂O band. Between 240 and 190 K and between 140 and 90 K in the spectra of FeSO₄.4H₂O, two potential phase transitions have been identified from the changes in the lattice and water‐stretching regions. The resolution of the ν₁(H₂O) and ν₃(H₂O) bands in FeSO₄·4H₂O and FeSO₄·H₂O also improved sharply at low temperatures. The capability of distinguishing various forms of FeSO₄ hydrates unambiguously makes the Raman technique a potential analytical tool for the identification of sulfate minerals on planetary surfaces. Copyright © 2006 John Wiley & Sons, Ltd.     

反应气压对直流磁控反应溅射制备的氧化银薄膜的结构和光学性质的影响

利用直流磁控反应溅射技术,通过调节反应气压(RP),在250 ℃衬底温度下制备了一系列氧化银 (Ag_xO) 薄膜,并利用X射线衍射谱、能量色散谱和分光光度计重点研究了RP对Ag_xO薄膜的结构和光学性质的影响. 研究结果表明,随着RP从0.5 Pa升高到3.5 Pa,薄膜明显呈现了从两相(AgO+Ag₂O)到单相(Ag₂O)结构再到两相(Ag₂O+AgO)结构的演变. 特 关键词： 氧化银薄膜 直流磁控反应溅射 X射线衍射谱 光学性质     

One-pot synthesis of single-crystalline Cu2O hollow nanocubes

Single-crystalline Cu₂O hollow nanocubes have been successfully synthesized via a simple wet chemical route in the absence of any surfactants or templates. By studying the growth process of the Cu₂O hollow nanocubes, we found that the Cu₂O hollow nanocubes were formed through a reducing and simultaneously etching process. The speed of reducing Cu(OH)₂ into Cu₂O was much faster than the speed of etching Cu₂O. As a result, Cu₂O solid nanocubes were firstly formed, and then the solid nanocubes were gradually etched into hollow nanocubes.     

Composition and Structure of Complexes Formed in Aqueous Solutions of Trifluoroacetic Acid According to IR Spectroscopy Data

The composition and structure of complexes that formed in aqueous solutions of trifluoroacetic acid were studied by frustrated multiple total internal reflection IR spectroscopy (FMTIR). Two types of complexes with a molecular structure formed: trimers CF₃COOH · (H₂O)₂ and cyclic tetramers (CF₃COOH)₂ · (H₂O)₂, in which the molecules of the components are arranged in pairs. In the range of acid concentrations from 100% to [H₂O]/[CF₃COOH] = 1: 1, only these tetramers formed, and all added water was bound into these hydrates. In more dilute solutions (up to [H₂O]/[CF₃COOH] = 2: 1), CF₃COOH · (H₂O)₂ complexes formed along with tetramers; at a double excess of H₂O, the components of the solution were completely bound into these trimers. In dilute solutions (from 0 to 3.6 M CF₃COOH), the acid is completely dissociated into H₅O ₂ ⁺ and CF₃COO^– ions hydrated with water molecules. In the range of medium concentrations (from 3.6 M to [H₂O]/[CF₃COOH] = 2: 1), the solutions contain both these ions and CF₃COOH · (H₂O)₂ dihydrates. For this range of compositions of the CF₃COOH?H₂O system, the concentrations of H₅O ₂ ⁺ ions and CF₃COOH · (H₂O)₂ dihydrates were calculated.     

Atomic-scale studies of native point defect and nonstoichiometry in silicon oxynitride

The native point defects and mechanism of accommodating deviations from stoichiometry of Si₂N₂O crystal have been investigated using atomistic simulation techniques. This work firstly provides a reliable classical interatomic potential model derived from density functional theory calculations. The force-field parameters well reproduce the crystal structure, elastic stiffness, and dielectric constants of Si₂N₂O. It is expected that the force-field parameters are useful in future investigations on Si₂N₂O by molecular dynamic simulation. The calculated formation energies for native defects suggest that intrinsic disorder in stoichiometric Si₂N₂O is dominated by antisites and a degree of oxygen Frenkel defect may also exist in this system. In nonstoichiometric Si₂N₂O, the calculated reaction energies indicate that excess SiO₂ or Si₃N₄ is most likely accommodated by the formation of antisite in the lattice. And we also find that SiO₂ excess is energetically more favorable than Si₃N₄ surplus in Si₂N₂O.