Idle spin behavior of the shifted hexagonal tungsten bronze type compounds FeIIFeIII2F8(H2O)2 and MnFe2F8(H2O)2

Fe^IIFe^III₂F₈(H₂O)₂ and MnFe₂F₈(H₂O)₂, grown by hydrothermal synthesis ($\text{P ? 200}\text{MPa}\text{, T = 450}\text{or}\text{380°}\text{C}$), crystallize in the monoclinic system with cell dimensions (Å): a = 7.609(5), b = 7.514(6), c = 7.453(4), β = 118.21(3)°; and a = 7.589(6), b = 7.503(8), c = 7.449(5), β = 118.06(3)°, and space group $\text{C2}\text{m}\text{, Z = 2}$. The structure is related to that of $\text{WO}{}_3\text{·}\text{1}\text{3}\text{H}{}_2\text{O}$. It is described in terms of perovskite type layers of Fe³⁺ octahedra separated by Fe²⁺ or Mn²⁺ octahedra, or in terms of shifted hexagonal bronze type layers. Both compounds present a weak ferromagnetism below T_N (157 and 156 K, respectively). Mössbauer spectroscopy points to an “idle spin” behavior for Fe^IIFe^III₂F₈(H₂O)₂: only Fe³⁺ spins order at T_N, while the Fe²⁺ spins remain paramagnetic between 157 and 35 K. Below 35 K, the hyperfine magnetic field at the Fe²⁺ nuclei is very weak: H_hf = 47 kOe at T = 4.2 K. For MnFe₂F₈(H₂O)₂, Mn²⁺ spin disorder is expected at 4.2 K. This “idle spin” behavior is due to magnetic frustration.     

Relative formation of ground- and excited-state NO−2 in collisions of fast metastable atoms and molecules (Ar*, H*, D*, H*2, D*2) with NO2

Collisions ot fast metastable beams of Ar, H, and D atoms, and H₂ and D₂ molecules with NO₂ producing positive ions and NO^?₂ were studied. The ratio of the ³B₁-¹A₁ NO^?₂ cross sections is a linear function of the projectile velocity. This finding is tentatively interpreted in the framework of a Landau-Zener model Earlier results on O^?₂ are re-examined.     

Pseudopotential calculations on Rb+2, Cs+2, RbH+, CsH+ and the mixed alkali dimer ions

Semi-empirical pseudopotentials are used in calculating the ground-state potentials curves for single valence-electron molecular ions. Very accurate results are obtained and a number of predictions given. The ionization energies of the neutral dimers are evaluated. A spectroscopic rule enables us to estimate the A ¹Σ⁺ state of KRb and RbCs.     

Mobilities of H+3 and HeH+ ions in helium gas and rate coefficient for HeH+ + H2 → H+3 + He

The mobilities of mass-identified H⁺₃ and HeH⁺ ions in helium and the reaction rate coefficient for HeH⁺ + H₂ → H⁺₃ + He have been measured by a drift-tube quadrupole mass spectrometer at 300 K. The zero-field reduced mobilities of H⁺₃ and HeH⁺ ions, corrected to 273 K, are 31.0 ± 0.8 and 23.4 ± 0.6 cm² V^?1 s^?1 respectively. The reaction rate coefficient was found to be (1.26 + 0.16) × 10^?9 cm³s^?1 and was observed to be independent of the mean ion kinetic energy in the range from 0.04 to 0.3 eV.     

Structure and properties of H2CN,H2CC−, H2BO and H2CO+

Ab initio SCF—MO calculations are presented for H₂CN, H₂CC^?, H₂BO and H₂CO⁺, including geometry optimization. One-electron properties are presented and compared with experiment where possible, particularly ESR hyperfine data.     

Photodissociation of the dimer ions Ar+2, Ne+2, and (CO2)+2

The tandem quadrupole photodissociation mass spectrometer has been used to study photodissociation reactions of Ar⁺₂, Ne⁺₂, and (CO₂)⁺₂. The cross sections for photodissociation of Ar⁺₂ exhibited a strong dependence on ion source pressure, varying from 2 × 10 ^?18cm² at 0.1 torr to 6 × 10^?19cm² at 0.5 torr. A large photodissociation cross section (2 × 10^?17cm² for the reaction (CO₂)⁺₂ → CO⁺₂+ CO₂ was observed at the red end of the visible spectrum (580–620 nm) suggesting that this may be an important reaction in CO₂ rich planetary ionspheres such as that of Mars.     

The effect of inner-shell polarization on diagonal stretching force constants Part III. ACCD results for HF, OH, NH3, N2, F2 and H2CO

Results of quadratic stretching force-constant determinations at the TZ + P ACCD and TZ + 2P ACCD levels, in which the second set of polarization functions has been optimized to account for inner-shell polarization (ISP), are presented. Essentially perfect agreement with experiment was found in the cases of HF and NH₃ when inner-shell polarization was taken into account. Although in other test cases errors in the force constants arise from other sources, improvement in the force constant is observed on inclusion of ISP functions in the basis.     

Solid-state decomposition studies on fluoroperoxo species of transition metals. Part VI. Kinetics of isothermal decomposition of M2Zr2(O2)2F6 · 2 H2O (M = Rb+, or Cs+)

The decomposition of solid fluoroperoxozirconates of alkali metals, M₂Zr₂(O₂)₂F₆ · 2 H₂O (M = Rb⁺, Cs⁺), is carried out in vacuum under isothermal conditions. The stoichiometry of the reaction may be represented by the equation, M₂Zr₂(O₂)₂F₆ · 2 H₂O(S) — M₂Zr₂O₂F₆(s) + O₂(g) + 2 H₂ O(g) (condensed). The fractional decomposition α is determined by measuring the pressure of oxygen evolved during pyrolysis with a McLeod gauge. The α values range from 0.06 to 0.70 for the rubidium and from 0.06 to 0.79 for the caesium species in the temperature ranges 107–202°C and 101–219°C, respectively. The α—time data for both compounds show that the kinetics are deceleratory throughout the course of the decomposition reaction. In both compounds, the initial stages of decomposition are described by a unimolecular decay law, while the later stages obey a contracting volume equation at all temperatures. The activation energies from Arrhenius plots are 14.0 and 10.9 kcal mole^?1 for the rubidium and 12.9 and 11.2 kcal mole^?1 for the caesium compound.     

Correlation effects on hydrogen-bond potentials. SCF Cl calculations for the systems HF−2 and H3O−2

The effects of neglecting electron correlation in the Hartree-Fock approximation have been investigated for selected properties of two strongly hydrogen-bonded systems. Accounting for correlation will substantially lower and, in some cases, remove barriers for proton transfer which have been obtained using the Hartree-Fock approximation. As a consequence, the asymmetric hydrogen-bond stretching frequencies in HF^?₂ are found to increase when correlation is included in the calculations, contrary to the case for more regular stretching frequencies. The hydrogen-bond energies of the two systems are found to be rather insensitive to correlation effects.     

Preparation, Thermal Behaviour, and Crystal Structure of MgAl2F8(H2O)2

 Single crystals of MgAl₂F₈(H₂O)₂ have been obtained under hydrothermal conditions (250°C, 14 d) from a starting mixture of AlF₃ and MgAlF₅(H₂O)₂ in a 5% (w/w) HF solution. The crystal structure has been determined and refined from single crystal data (Fmmm (#69), Z = 4, a = 7.2691(7), b = 7.0954(16), c = 12.452(2) ?, 281 structure factors, 27 parameters, R(F ² > 2σ (F ²)) = 0.0282, wR(F ² all) = 0.0885). The obtained crystals were systematically twinned according to (010/100/001) as twinning matrix, reflecting the pseudo-tetragonal metric. The crystal structure is composed of perowskite-type layers built of corner sharing AlF₆ octahedra with an overall composition of AlF₄ ⁻ which are connected via common fluorine atoms of [MgF_4/2(H₂O)_2/1] octahedra. Group-subgroup relations of MgAl₂F₈(H₂O)₂ to WO₃(H₂O)_0.33 and to other M(II)M(III)₂ F₈(H₂O)₂ structures are briefly discussed. Above 570°C, MgAl₂F₈(H₂O)₂ decomposes under elimination of water into α-AlF₃, β-AlF₃, and MgF₂.     

Low energy crossed beam study of the endothermic charge transfer reaction H+2(Ar,H2)Ar+

A crossed beam study of the title reaction if reported, from 0.45 to 7.8 eV. The reaction is predominantly translationally endothermic. At the lowest energy, there is evidence for two reaction paths: a long-range electron transfer and an intimate collision with electron transfer. Branching ratios for the competitive proton transfer reaction are presented.     

气相和水溶液中铀酰配合物UO2L 2-n*an (L=F-, CO2-3, NO-3; n=0-6, a=1, 2)的结构和振动光谱

通过对铀采用相对赝势基组, 其它原子使用6-31+G(d)基组, 应用密度泛函理论(DFT)以及B3LYP方法对UO2+2离子与F-、CO2-3和NO-3的各配位结构进行优化和频率计算. 计算考虑了气相和水溶剂化两种状态, 其中溶剂化模型采用连续导体介质理论模型(CPCM). 计算结果显示配体的配位数与O=U=O对称伸缩振动频率存在线性关系. 配体在气相和水溶液中存在的关系基本符合通式: νs=-Agasn+983和νs=-Aaqn+821(Agas 和Aaq为常数, 表示每增加一个配体振动频率的变化值; n为配体配位数). 其中F-对应Agas=53 cm-1, Aaq=11 cm-1; CO2-3对应Agas=85 cm-1, Aaq=19 cm-1; NO-3对应Agas=48 cm-1, Aaq=-10 cm-1. 并且Aaq值与实验值一致.     

Endothermic reactions of Ni+ with H2, HD and D2

An ion-beam apparatus is employed to study the reaction of Ni⁺ with H₂, HD, and D₂ as a function of kinetic energy. These reactions lead to the endothermic formation of NiH⁺, NiH⁺ and NiD⁺, and NiD⁺, respectively. Interpretation of the threshold for these processes yields the average bond energies, D⁰(Ni⁺H) = 1.86 ± 0.09 eV and D⁰(Ni⁺D) = 1.90 ± 0.14 eV. The total reaction cross sections for all three systems are similar; however, a striking isotope effect is observed for Ni⁺ reacting with HD. The dependence of the cross sections on relative kinetic energy is discussed in terms of simple models for reaction.     

Electronic nonadiabatic transitions in the reactive (Ar+ + H2, Ar + H+2, ArH+ + H) system. Numerical results for the collinear configuration

In this communication are presented exact quantum mechanical nonadiabatic electronic transition probabilities for the collinear reaction Ar⁺ + H₂(v_i = 0) → ArH⁺(v_f) + H. The calculations were performed using a potential surface calculated by the DIM method. It is established that large probabilities (≈ 1.0) can be obtained only if there is enough translational energy to overcome a potential barrier formed due to the crossing between v_i = 0 of the Ar⁺ + H₂ system and v_i = 2 of the Ar + H⁺₂ system. The threshold for the reaction is found to be 0.06 eV.     

Observation of far-infrared transitions of HCO+, CO+ and HN+2

Rotational transitions of molecular ions HCO⁺, CO⁺, and HN⁺₂ have been observed at frequencies aroud 1 THz. The ions were produced in the negative glow of a hollow cathode discharge cooled by liquid nitrogen. Preliminary results indicate efficient production of ions in an absorption cell of simple construction.     

Explanation for the structural differences of S2+4, S04 and S2−4

An explanation for the geometry changes upon successive double reductions of S²⁺₄ (square planar, D_4h symmetry) to neutral S₄ (for which the structure is unknown) and finally to S^2?₄ (non-planar, C₂ symmetry) is given on the basis of orbital eigenvalues and wavefunctions calculated with the self-consistent-field Xα scattered-wave molecular orbital method.     

Rotational analysis of the 201 and 211 bands in the Ã2Σ+-X̃ 2Π spectrum of N2O+

Analysis of new emission spectra of òΣ⁺-X? ²Π in N₂O⁺, including the forbidden components with Δν₂ = 1, have made it possible to locate all four vibronic components of the ν″₂ = 1 manifold. Principal rotational constants and spinvibronic terms are given. A previous estimate of the Renner parameter is revised to a value of ?0.179 ± 0.002.     

Fluorescence quantum yields and cascade-free lifetimes of state selected CO+2, COS+, CS+2 and N2O+ determined by photoelectron—photon coincidence spectroscopy

The details and principles of an apparatus built for measurements of fluorescence quantum yields and cascade-free lifetimes of open-shell cations are reported. These rely on the detection of coincidences between energy selected photoelectrons and undispersed photons. The results of such measurements for CO⁺₂, COS⁺, CS⁺₂ and N₂O⁺ in selected vibrational levels of their excited states are presented. Non-unity fluorescence quantum yields are found for some vibronic levels of CO⁺₂($\text{B}$), COS⁺ ($\text{A}$), N₂OP⁺($\text{A}$) and a non-exponential decay is observed for CS⁺₂($\text{A}$). The data yield the following values for the radiative lifetimes: CO⁺₂($\text{A}$) 124 ± 6 ns, CO⁺₂($\text{B}$) 140 ± 7 ns, COS⁺($\text{A}$) 550 ± 50 ns and N₂O⁺($\text{A}$) 240 ± 12 ns.     

Solution raman spectra and normal coordinate analysis of the H3CPH+3 and H3CPD+3 cations

The Raman spectra of solutions of H₃ CPH₃⁺ and H₃ CPD₃⁺ in aqueous concentrated hydrochloric and deuterochloric acid are reported together with polarisation data. A complete vibrational assignment is given on the basis of C_3v, symmetry except for the inactive A₂ mode. A set of valence force constants and potential energy distributions have been calculated from the data of the two isotopes H₃ CPH₃ and H₃⁺ CPD⁺₃. For H₃ CPD⁺₃ the potential energy distribution demonstrates strong interaction between the P-C stretching and the symmetrical PD₃ deformation mode.     

Jahn-Teller-distorted dimeric anions in (cat)[Mn2F8(H2O)2]·2H2O (cat = pipzH2, dabcoH2) and (dabcoH2)2[Mn2F8(H2PO4)2]

Using biprotonated dabco (1,4-diazabicyclo[2.2.2]octane) or pipz (piperazine) as counter cations, mixed-ligand fluoromanganates(III) with dimeric anions could be prepared from hydrofluoric acid solutions. The crystal structures were determined by X-ray diffraction on single crystals: dabcoH₂[Mn₂F₈(H₂O)₂]·2H₂O (1), space group P2₁, Z = 2, a = 6.944(1), b = 14.689(3), c = 7.307(1) Å, β = 93.75(3)°, R₁ = 0.0240; pipzH₂[Mn₂F₈(H₂O)₂]·2H₂O (2), space group , Z = 2, a = 6.977(1), b = 8.760(2), c = 12.584(3) Å, α = 83.79(3), β = 74.25(3), γ = 71.20(3)°, R₁ = 0.0451; (dabcoH₂)₂[Mn₂F₈(H₂PO₄)₂] (3), space group P2₁/n, Z = 4, a = 9.3447(4), b = 12.5208(4), c = 9.7591(6) Å, β = 94.392(8)°, R₁ = 0.0280. All three compounds show dimeric anions formed by [MnF₅O] octahedra (O from oxo ligands) sharing a common edge, with strongly asymmetric double fluorine bridges. In contrast to analogous dimeric anions of Al or Fe(III), the oxo ligands (H₂O (1,2) or phosphate (3)) are in equatorial trans-positions within the bridging plane. The strong pseudo-Jahn-Teller effect of octahedral Mn(III) complexes is documented in a huge elongation of an octahedral axis, namely that including the long bridging Mn-F bond and the Mn-O bond. In spite of different charge of the anion in the fluoride phosphate, the octahedral geometry is almost the same as in the aqua-fluoro compounds. The strong distortion is reflected also in the ligand field spectra.