Photofragmentation of hydrated iron ions Fe(HO) () at 532, 355 and 266 nm

Photofragmentation of Fe(H₂O)n ⁺ clusters (n =1-9) is investigated at three different wavelengths, 532, 355 and 266 nm. Two fragmentation pathways are observed depending essentially on the photon energy, but also on the parent size n. The fragmentation products belong to two ion families, Fe(H₂O)m ⁺ and FeOH(H₂O)m ⁺ , which correspond to dehydration and intracluster dehydrogenation reactions respectively. The ion yields are studied as a function of the laser fluence in order to determine the number of photons implied in the photofragmentation process. This allows us to estimate that the D[(H₂O)_n-1Fe^+-(H₂O)] bond energy is ranging between 0.44 eV and 0.55 eV for .Photon absorption cross sections are also derived from the fluence experiments, and two different behaviors are observed: i) At 355 nm, far away from any transition, progressive solvation of the metal ion results in an increasing absorption cross section from n =2 to n =9. This can be attributed to a forbidden transition of bare , which becomes progressively allowed because of the interaction with more and more water ligands. ii) At 266 nm, close to several allowed transitions of bare , a distinct maximum is observed for the absorption of ion. It may be attributed to a change in the spin multiplicity when switching from and on one hand to Fe(H₂O) on the other. Received: 11 November 1997 / Revised: 18 February 1998 / Accepted: 22 April 1998     

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.     

The role of OH ions in the stabilization of F colour centres in LiF

Thermally Stimulated Depolarisation Current (TSDC) and optical methods are applied to a range of alkali-fluoride crystals in order to establish a model for the stable F ₂ ⁺ - like colour centres in LiF:OH^-. The experimental results for LiF:OH^- suggest that the OH^- defects are partially destroyed under ionising irradiation or during crystal growth. The low-temperature dielectric relaxation signals in LiF:OH^- and LiF:Mg²⁺,OH^- are attributed to highly interacting hydroxide ions and products of their destruction located in extended lattice defects. In LiF:OH^-, in contrast to other alkali halides, the results advocate for a defect-structure model, which considers a neutral defect (ND, probably O₂ or H₂) sited at the anion vacancy of the O^2--V _a ⁺ dipole and which possibly is the “nucleus” for the F ₂ ⁺ centre. The proposed F ₂ ⁺ (ND, O^-) model seems to better explain the dielectric results, compared to the older F ₂ ⁺ (O^2-) and F ₂ ⁺ (O^-) models. The estimate for the electric dipole moment derived from the experimental TSDC bands, gives a value for the F ₂ ⁺ - like centre in LiF:OH^- between those of the F ₂ ⁺ (O^-) and F ₂ ⁺ (O^2-) defects, in good agreement with the proposed F ₂ ⁺ (ND,O^-) model. The reduction of the activation energy barrier of the (re)orientation process of the Mg²⁺V _c ^- (OH^-) complexes in LiF:Mg²⁺,OH^-, and the low-temperature shift of their TSDC band, compared to the single Mg ₂ ⁺ V _c ^- peak in LiF:Mg²⁺, are tentatively ascribed to an increase in the crystal-lattice parameters owing to the presence of OH^- and/or products of its destruction. Received 31 August 2001 / Received in final form 30 March 2002 Published online 9 July 2002     

Characterisation of the Fermi surface and phase transitions of (BEDO-TTF)2 ReO4·(H2O) by physical property measurements and electronic band structure calculations

The electronic properties of the organic superconductor (BEDO-TTF)₂ ReO₄·(H₂O) were investigated by temperature dependent resistivity, ESR, Hall effect and magnetoresistance measurements. Shubnikov-de Haas (SdH) oscillations were observed in magnetic fields up to 24 T in the temperature range 0.5 K to 4.2 K. The electronic band structure of (BEDO-TTF)₂ ReO₄·(H₂O) was calculated by employing the extended Hückel tight binding method on the basis of its room temperature crystal structure. The two observed SdH frequencies of 75 T and 37 T correspond very well with two cross-sectional areas of the hole and electron Fermi surface pockets obtained from the tight binding calculation. From the temperature dependence of the SdH oscillation amplitudes, the cyclotron effective mass (m_c) belonging to the larger and smaller pockets were found to be 0.9 m₀ and m_c=1.15 m₀ respectively. Measurements of the angular dependence of the SdH frequencies show no deviation from that expected for a cylindrical Fermi surface. In terms of our tight binding calculations and experimental measurements, probable causes for the 213 K and 35 K phase transitions are discussed. The calculations show that (BEDO-TTF)₂ ReO₄·(H₂O) is a two dimensional semimetal but possesses a hidden nesting. The latter is likely to cause an SDW instability leading to the 35 K transition. The resistivity drop associated with the 213 K transition is likely to be induced by an abrupt increase in the relaxation time. The excellent agreement between the calculated and experimentally observed Fermi surface implies that, with decreasing temperature below 35 K, (BEDO-TTF)₂ ReO₄·(H₂O) gradually gets out of the SDW state and re-enters the original metallic state, in which it becomes superconducting below 2.4 K.Reported at the 13th Genral Conference of the Condensed Matter Division of the European Physical Society, Regensburg, March 1993     

Unconventional field and angle dependences of the Shubnikov-de Haas oscillations spectra in the quasi two-dimensional organic superconductor (BEDO-TTF) 2ReO 4H 2O

We report on the inter-layer oscillatory conductance of the two-dimensional organic superconductor (BEDO-TTF)₂ReO₄H₂O measured in static and pulsed magnetic fields of up to 15 and 52 T, respectively. In agreement with previous in-plane studies, two Shubnikov-de Haas oscillation series linked to the two electron and the hole orbits are observed. The influence of the magnitude and orientation of the magnetic field with respect to the conducting plane is studied in the framework of the conventional two- and three-dimensional Lifshits-Kosevich (LK) model. Deviations of the data from this model are observed in low fields strongly tilted with respect to the normal to the conducting plane. In this latter case, the observed behaviour is consistent with an unexplained lowering of the cyclotron effective mass. At high magnetic field, the oscillatory data could have been compatible with the occurrence of a magnetic breakdown orbit built from the hole and electron orbits. However, the increase of the cyclotron effective mass, linked to the electron orbits, as the magnetic field increases above ∼12 T is consistent with a field-induced phase transition. In the lower field range, where the conventional LK model holds, the analysis of the angle dependence of the oscillations amplitude suggests significant renormalisation of the effective Landé factor. Received 22 August 2000 and Received in final form 20 December 2000     

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.     

Systematic field-theory for the hard-core one-component plasma

A continuous liquid flow in a vacuum (a liquid beam) of an aqueous solution of adenine salt containing hydrochloric acid or sodium hydroxide was irradiated with an intense pulsed IR laser at 3 μm, which is resonant to a vibrational mode related to the OH stretch vibration of H₂O. Neutral species isolated into the vacuum were ionized by a pulsed UV laser at 270 nm, and the product ions were mass-analyzed by a time-of-flight mass spectrometer. It is found that AH ₂ ^{2 + .} 2Cl^- and [A-iH] ^{i - .} iNa⁺ (i = 1-3) are isolated in the vacuum from the aqueous acidic and alkaline solutions, respectively, under irradiation of the IR laser, and undergo four-photon ionization involving decomposition and proton transfer of the intermediate species under irradiation of the UV laser. Received 1st May 2002 Published online 13 September 2002     

Synthesis of ultrasmall magnetic iron oxide nanoparticles and study of their colloid and surface chemistry

Colloidal nanoparticles of Fe₃O₄ (4 nm) were synthesized by high-temperature hydrolysis of chelated iron (II) and (III) diethylene glycol alkoxide complexes in a solution of the parent alcohol (H₂DEG) without using capping ligands or surfactants: [Fe(DEG)Cl₂]²⁻+2[Fe(DEG)Cl₃]²⁻+2H₂O+2OH⁻→Fe₃O₄+3H₂DEG+8Cl⁻ The obtained particles were reacted with different small-molecule polydentate ligands, and the resulting adducts were tested for aqueous colloid formation. Both the carboxyl and α-hydroxyl groups of the hydroxyacids are involved in coordination to the nanoparticles’ surface. This coordination provides the major contribution to the stability of the ligand-coated nanoparticles against hydrolysis.     

KDP晶体固-液界面吸附行为的分子模拟研究

通过构建晶体表面-KDP分子界面吸附结构模型, 采用分子动力学和密度泛函计算方法研究KDP分子在(001)和(010)面吸附的物理化学过程, 考察了温度对物理吸附行为的影响. 研究表明: KDP晶体表面的吸附过程和生长习性主要由化学吸附主导, 化学吸附能的计算表明[K-O₈]基元在(001)界面的结合能是(010)界面结合能的2.86倍; 在饱和温度附近, [H₂PO₄]^-阴离子在KDP界面的物理结合能随温度的变化呈现振荡特征, 溶液中有较多的离子团簇形成, 溶液变得很不稳定; 当温度从323 K降低至308 K时, 水分子在界面的结合能总体呈下降趋势, 而KDP分子在界面的吸附能总体呈上升趋势, 脱水过程是水分子和[H₂PO₄]^-阴离子在固液界面边界层竞争吸附的结果. 研究结果对确足晶体生长界面动力学过程发展和完善晶体生长理论有重要意义. 关键词： 分子动力学 双层结构模型 结合能     

Crystal structure analysis of novel complex hydrides formed by the combination of LiBH4 and LiNH2

Combination of LiBH₄ and LiNH₂ by ball milling forms the series of novel complex hydrides Li₂BNH₆, Li₃BN₂H₈ and Li₄BN₃H₁₀, depending on the combination ratios. The crystal structure of Li₄BN₃H₁₀ analyzed by synchrotron X-raydiffraction measurements is determined to be a cubic system (space group: I2₁3) with the lattice constant of a=10.673(2)Å. It should be emphasized that Li₄BN₃H₁₀ is an ionic crystal which is composed of a lithium cation Li⁺ and two different kinds of the complex anion [BH₄]^- and [NH₂]^-. These anions are located in the vertex and face-center of the cubic sub-lattice, and the lithium cation Li⁺ in the interstitial site between the anions, respectively. The other series of complex hydrides, Li₂BNH₆ and Li₃BN₂H₈, are also predicted to possess similar structures composed of a lithium cation Li⁺ and two different kinds of the complex anion [BH₄]^- and [NH₂]^-.     

Cross-section and rate coefficient calculation for electron impact excitation, ionisation and dissociation of H2 and OH molecules

The weighted total cross-section (WTCS) theory is used to calculate electron impact excitation, ionisation and dissociation cross-sections and rate coefficients of OH, H₂, OH⁺, H₂ ⁺, OH^- and H₂ ^- diatomic molecules in the temperature range 1500–15000 K. Calculations are performed for H₂(X, B, C), OH(X, A, B), H₂ ⁺(X), OH⁺(X, a, A, b, c), H₂ ^-(X) and OH^-(X) electronic states for which Dunham coefficients are available. Rate coefficients are calculated from WTCS assuming Maxwellian energy distribution functions for electrons and heavy particles. One and two temperature (θ_e and θ_g respectively for electron and heavy particles kinetic temperatures) results are presented and fitting parameters (a, b and c) are given for each reaction rate coefficient: k(θ) = a (θ^b)exp (-c/θ).     

Steric effect in O+/H2 and H+/H2O collisions

The positive water and hydronium ions are of interest in a variety of chemical and biological applications. Here we study the steric effect in charge transfer collisions, i.e. the spatial dependence of single electron capture, in collisions mediated by these ions. In particular, the steric effect is demonstrated in the O⁺(²D)/H₂ and H⁺/H₂O charge transfer collisions in the energy range of 100 eV/amu to 10 keV/amu.     

SIMS and TDS study of the reaction of water and oxygen on Pt(111)

The reaction of H₂¹⁶O with ¹⁸O on Pt(111) was investigated using temperature programmed static secondary ion mass spectrometry (TPSSIMS), SSIMS and thermal desorption spectroscopy (TDS). The TPSSIMS behavior of the H₃O⁺ and H₃¹⁸O⁺ signals, after coadsorption of the reactants at 95 K, indicates that the isotopic exchange rate increases sharply at temperatures above 130 K. At 150 K, hydroxyl formation is indicated by a sharp drop in the H₃O⁺ and a similar sharp increase in the H₃¹⁸O⁺ signals. Using TDS, the overall stoichiometry of the reaction was determined to be 2H₂O(a)+O(a)→ 3 OH(a)+H(a). SSIMS data suggest that at least two kinds of hydroxyls are formed and that they do not interconvert at 160 K.     

通过盐酸刻蚀和生长作用来选择性合成不同尺寸大小的金纳米团簇

Controllable syntheses of different-sized gold nanoclusters are of great significance for their fundamental science and practical applications.In this work,we achieve the controllable and selective syntheses of Au₇ and Au₁₃ clusters through adding HCl to the traditional Au₁₁ synthetic route at different reaction time.Time-dependent mass spectra and UVVis spectra were employed to monitor these two HCl-directed processes,and revealed the distinct roles of HCl as an etchant or a growth promotor,respectively.Furthermore,parallel experiments on independent synthetic routes involving only non-chlorine H⁺(acetic acid) or Cl^-(tetraethy lammonium chloride) instead of HCl were performed,which illustrated the main role of H⁺-etching and Cl^--assisted growth in HCl-directed cluster synthetic routes.We propose the HCl-etching is mainly achieved via the H⁺ action to break the Au (I)-PPh₃ part of clusters,while the HCl-promoted growth is realized via the attachment of Au-Cl species to the pre-formed clusters.     

Ion and solvent transport in polypyrrole: Experimental test of osmotic model

Ion and solvent transport in the conjugated polymer actuator material, polypyrrole doped with the immobile anion dodecyl benzene sulphonate, has been investigated by simultaneous cyclic voltammetry and Electrochemical Quartz Crystal Microbalance measurements. The purpose was to elucidate the precise nature of the mobile species during redox cycling, and to seek confirmation for the osmotic mechanism of actuation. Three testable aspects of the model were confirmed: The number of inserted H₂O molecules decreases with electrolyte concentration; at the same time the mechanism gradually changes from almost pure cation transport to ca. equal amount of anion transport; exchanging Br⁻ for Cl⁻ ions has only negligible effect at lower concentrations at equal osmotic pressures. Approximately, 4 H₂O molecules are tightly bound to each Na⁺ ion at concentrations <1 M. Paper presented at the International Conference on Functional Materials and Devices 2005, Kuala Lumpur, Malaysia, June 6 – 8, 2005.     

A tunable diode laser system for the remote sensing of on-road vehicle emissions

2 O, and NO₂ emissions have been measured with this instrument. The system is also capable of measuring CO, NH₃, H₂CO, CH₃OH, and other small molecules in vehicle exhaust. Received: 18 May 1998/Revised version: 1 July 1998     

A DFT study of reduction of nitrobenzene to aniline with SnCl2 and hydrochloric acid

A fundamental reduction reaction, nitrobenzene to aniline in SnCl₂ and hydrochloric acid, was investigated by density functional theory (DFT) calculations. First, the change of SnCl₂ → SnCl₄^2? → Cl₄SnH^? was discussed, and the reaction path of SnCl₄^2? + H₃O⁺ → Cl₄SnH^? + H₂O was obtained. Starting from nitrobenzene, six elementary processes were found so as to arrive at the protonated aniline. The hydride ion from Cl₄SnH^? is connected always to the cationic nitrogen, and the proton is always to oxygens. An intermediate Ph?N⁺H₂OH was obtained, which is isomerized to the para O?H adduct protonated imine via the Bamberger rearrangement. This species may undergo the H^? acceptance at the sp² N⁺H₂ center. In the nitrobenzene reduction, the proton enhances the electrophilicity of the nitrogen center, which makes the hydride shift ready. N?H bonds are formed, and N?O bonds are cleaved both by the proton attach and subsequent H₂O elimination and by the formal [1,5] OH shift. Copyright © 2016 John Wiley & Sons, Ltd.     

Electron detachment and fragmentation in collisions between 1.25 keV/carbon and clusters and

The destruction cross-section for 22.5 and 50 keV C^1- , for 10 and 50 keV C₈ ^1- and for 50 and 75 keV C₆₀ ^1- clusters in collisions with H₂ has been measured by an attenuation method. The destruction of the cluster anions is dominated by electron detachment rather than fragmentation and is of the order of the geometric cross-section. The cross-sections vary little with bombarding energy. Received: 16 September 1998 / Received in final form: 23 February 1999     

Reactivity and XAFS study on (1−x)CeO2-xNiO (x=0.025-0.3) system in the two-step water-splitting reaction for solar H2 production

The redox reaction of Ce⁴⁺-Ce³⁺ promoted by the catalytic function of nickel ions in a (1−x)CeO₂-xNiO solid solution was investigated for solar H₂ production by the two-step water-splitting reaction. By irradiation using an infrared imaging lamp as a solar simulator, the O₂-releasing reaction with (1−x)CeO₂-xNiO solid solution proceeded at 1673-1873 K, and its reduced form was produced. The amounts of H₂ gas evolved by the reduced form were 1.2-2.5 cm³/g and the evolved gases amounts ratio of H₂/O₂ was nearly 2, which is equal to the stoichiometric value of the water-splitting reaction (H₂O=H₂+1/2O₂). The maximum amounts of evolved H₂ and O₂ gases were obtained at the Ce:Ni mole ratio of 0.95:0.05 (x=0.05) in the (1−x)CeO₂-xNiO system. The X-ray absorption fine structure (XAFS) measurement showed that the O₂-releasing and H₂-generation reactions with (1−x)CeO₂-xNiO solid solution were repeatable with the redox system of Ce⁴⁺-Ce³⁺, which was enhanced by the catalytic function of Ni²⁺-Ni⁰.     

Structural characterisation of [Cu2(bptd) (H2O) Cl4] and [Ni2(bptd)2(H2O)4] Cl4·3H2O; evidence of null intramolecular exchanges by EPR and magnetic measurements

Using the 2,5-bis(2-pyridyl)-1,3,4-thiadiazole (bptd), we recently prepared [Cu₂(bptd) (H₂O) Cl₄] and [Ni₂(bptd)₂ (H₂O)₄] Cl₄, 3H₂O in which the magnetic centres are connected through one diazine+one chloro and two diazine ligand bridges, respectively. These two compounds are the first examples that show null intramolecular magnetic interactions despite M-M distances close to 3.7 Å within perfectly planar edifices:Down to , [Cu₂(bptd)Cl₄(H₂O)] is paramagnetic while, below T_t, half of the Cu²⁺ions interact, leading to residual paramagnetism of one Cu²⁺/f.u. Magnetic susceptibility measurements, EPR and pulsed EPR study indicate the original intermolecular nature of AF exchanges.[Ni₂(bptd)₂(H₂O)₄]Cl₄·3H₂O susceptibility obeys a Curie-law involving pure paramagnetism. Moreover, its EPR spectrum can be interpreted on the basis of virtual S=1 monomers. Below 70 K, Zero Field Splitting (D∼275 G) due to dipolar interactions without magnetic exchanges could be responsible for the LT spectra splitting. For both compounds, the thia role is suggested as partially responsible for the null-in-plane magnetic exchanges.