MB 8 2− (M = Be, Mg, Ca, Sr, and Ba): Planar octacoordinate alkaline earth metal atoms enclosed by boron rings

Complexes involving planar octacoordinate alkaline earth metal atoms in the centers of eight-membered boron rings have been investigated by two density functional theory (DFT) methods. BeB ₈ ^2? with D _8h symmetry is predicted to be stable, both geometrically and electronically, since a good match is achieved between the size of the central beryllium atom and the eight-membered boron ring. By contrast, the other alkaline earth metal atoms cannot be stabilized in the center of a planar eight-membered boron ring because of their large radii. By following the out-of-plane imaginary vibrational frequency, pyramidal C _8v MgB ₈ ^2? , CaB ₈ ^2? , SrB ₈ ^2? , and BaB ₈ ^2? structures are obtained. The presence of delocalized π and σ valence molecular orbitals in D _8h BeB ₈ ^2? gives rise to aromaticity, which is reflected by the value of the nucleus-independent chemical shift. The D _8h BeB ₈ ^2? structure is confirmed to be the global minimum on the potential energy surface.     

Theoretical study of the visible photodissociation spectrum of Ar 3 +

The photodissociation of Ar ₃ ⁺ is studied following a consistent theoretical approach from the Potential Energy Surfaces to the dynamics. Six P.E.S. are computed according to a D.I.M.-like model Hamiltonian. Transition dipole moments are determined using a similar method. The 4-D dynamics of this system is obtained with the H.W.D. method (Hemiquantal dynamic with the Whole DIM basis). All the 4 nuclear degrees of freedom and all the 6 electronic states are involved in the dynamical calculations, allowing for very general investigations. The main theoretical results are:

1. the spectrum essentially results from a Σ → Σg transition to the second excited electronic state along with a symmetric stretching motion
2. excited Ar ₃ ⁺ molecules almost all dissociate in Ar⁺ + 2 Ar
3. dissociation in Ar ₂ ⁺ + Ar requires special conditions such as low laser excitation and is predicted to increase with a specific excitation of the bending mode
4. the dominant symmetric stretching motion induces a bimodal kinetic energy distribution of the fragments.

All these points are in close agreement with experimental results.     

Guided ion beam studies of the reactions of O+, O 2 + , N+ and N 2 + with silane

Guided ion beam mass spectrometry is used to measure the cross sections as a function of kinetic energy for reaction of SiH₄ with O⁺(⁴S), O ₂ ⁺ (²Π_g,v=0), N⁺(³P), and N ₂ ⁺ (²Σ _g ⁺ ,v=0). All four ions react with silane by dissociative charge-transfer to form SiH _m ⁺ (m=0?3), and all but N ₂ ⁺ also form SiXH _m ⁺ products where (m=0?3) andX=O, O₂ or N. The overall reactivity of the O⁺, O ₂ ⁺ , and N⁺ systems show little dependence on kinetic energy, but for the case of N ₂ ⁺ , the reaction probability and product distribution relies heavily on the kinetic energy of the system. The present results are compared with those previously reported for reactions of the rare gas ions with silane [13] and are discussed in terms of vertical ionization from the 1t ₂ and 3a ₁ bands of SiH₄. Thermal reaction rates are also provided and dicussed.     

Effects of concentration and temperature on molar volumes of L-serine, L-isoleucine, and L-glutamine in aqueous NaCl and NaNO3 solutions

Densities of L-serine, L-isoleucine, L-glutamine in 1.5 mol kg^?1 aqueous NaCl, and NaNO₃ solutions have been measured for several molal concentrations of amino acids at temperatures from 298.15 to 323.15 K. The partial molar volumes (? _v ⁰ ) of L-serine, L-isoleucine, and L-glutamine in 1.5 mol kg^?1 aqueous NaCl/NaNO₃ solutions have been computed using density data. The transfer partial molar volumes (Δ_tr? _v ⁰ ) of L-serine, L-isoleucine, and L-glutamine from water to 1.5 mol kg^?1 aqueous NaCl/1.5 mol kg^?1 aqueous NaNO₃ solutions have been determined at 298.15 K. The trends of variation of ? _v ⁰ and Δ_tr? _v ⁰ with change in temperature have been discussed in terms of ion-ion, ion-hydrophilic, and ion-hydrophobic interactions operative in solutions.     

Photofragment spectroscopy of N 2 + in the near UV

Photofragment spectroscopy of N ₂ ⁺ has been studied in the wavelength range 343–404 nm using an excimer-pumped dye laser with a spectral resolution of 0.2 cm^?1. The observed bands are assigned to transitions from thev″=23?26 levels of theX ²Σ _g ⁺ state to highlying rovibrational levels (v′≈46–48) of theB ²Σ _u ⁺ state, forming quasibound (predissociating) states above the dissociation limit N⁺(³ P)+N(⁴ S ⁰). Measurement of the photofragment kinetic energies allows to establish an absolute energy scale for the transitions with respect to the dissociation limit. Molecular constants for the lower and upper states of the observed transitions are determined. The measurements allow the first direct determination of the N ₂ ⁺ dissociation energyD ₀ ⁰ (N ₂ ⁺ ). Some high-resolution (0.04 cm^?1) measurements show the fine-structure splitting and lifetime broadening of the excitation lines.     

The chemistry and physics of molecular surfaces

Configuration interaction calculations are carried out to study the potential energy surface for the system Ar-Ar ₂ ⁺ . An all-electron as well as a pseudopotential treatment is employed. It is found that in the perpendicular Ar approach the Ar ₂ ⁺ partner remains essentially unchanged and the potential can be characterized by an electrostatic ion-induced dipole interaction. In the collinear mode of Ar approach the Ar ₂ ⁺ bond separation increases considerably, the charge is redistributed and the interaction can be characterized as chemical bonding. The minimum on the surface is found to be the linear symmetric molecule with bond lengths of 2.62 Å. The optimum structure in the perpendicular approach lies 0.13 eV above the minimum and is the T-shaped molecule in which the Ar is 3.65 Å away from the midpoint of the Ar ₂ ⁺ (r=2.46 Å) system; the best equilateral triangle structure has a bond length of 2.99 Å but is found to lie 0.64 eV above the Ar ₃ ⁺ minimum. The dissociation energy into Ar ₂ ⁺ + Ar is calculated to be 0.16 eV in reasonable agreement with experimental values of 0.21 eV. The potential curves for the four lowest states of Ar ₂ ⁺ are also treated.     

Temperature and concentration dependences of density and refraction of aqueous duloxetine solutions

Present paper reports the measured densities (ρ) and refractive indices (n _D) of aqueous solutions of Duloxetine drug in wide range of molal concentrations (m = 0.0101–0.1031 mol kg^?1) and at different temperatures (297.15, 302.15, and 307.15 K). Apparent molar volumes (φ_v) of drug were calculated from density data and fitted to Masson’s relation \((\phi _\nu = \phi _\nu ^0 + S_\nu ^* \sqrt c )\) and partial molar volumes (φ _v ⁰ ) were evaluated at different temperatures. Concentration dependence of refractive index (n _D = Kc + n _D ⁰ ) at experimental temperature has been studied. Density and refractive index data has been used for the calculation of specific refractions (R _D). Experimental (ρ and n _D) and calculated (φ_v, φ _v ⁰ , and R _D) properties have been interpreted in terms of concentration and temperature effects on structural fittings and drug-water interactions.     

Helium cluster ions RgHe x + (Rg=Ne,Ar and Kr,x≦14) formed in a drift tube cooled by liquid helium

Rare gas ions Ne⁺, Ar⁺ and Kr⁺ are injected into a drift tube which is filled with helium gas and cooled by liquid helium. Helium cluster ions RgHe _x ⁺ (Rg=Ne, Ar and Kr,x≦14) are observed as products. Information regarding the stability of RgHe _x ⁺ is obtained from drift field dependence of the size distribution of the clusters, and magic numbers are determined. The magic numbers arex=11 and 13 for NeHe _x ⁺ andx=12 for ArHe _x ⁺ and KrHe _x ⁺ . NeHe _x ⁺ , Ar⁺ and Kr⁺ are proposed as the core ions for NeHe ₁₃ ⁺ , ArHe ₁₂ ⁺ and KrHe ₁₂ ⁺ , respectively.     

Magic numbers in sims of Mn similar to those of charged Ar clusters

Manganese cluster ions Mn _k ⁺ (k?60) have been produced by 7 keV Xe ion bombardment and analyzed by a double-focusing mass spectrometer. Discontinuous variations of intensity are found atk=5, 14, 16, 29, 34, 45 and 54. Most of these magic numbers coincide with or differ by only one from those observed in Ar _k ⁺ . The similarity in magic numbers between Mn _k ⁺ and Ar _k ⁺ indicates that the bonding nature in the charged Mn clusters is similar to that in the charged Ar clusters; The polarization force between a positive ion in the center of a cluster and surrounding neutral atoms is dominant binding force.     

Niobium-chloride octahedral clusters as building units for larger frameworks

A systematic theoretic study on clusters containing edge-bridged octahedral metal units [Nb₆Cl₁₂] ⁿ (n?=?2, 3, or 4) and a large variety of ligands has been performed. The benchmark results on the [Nb₆Cl ₁₂ ⁱ ] ⁿ⁺ and [Nb₆Cl ₁₂ ⁱ Cl ₆ ^a ] ⁿ (n?=?2, 3 or 4) cluster units demonstrated the reliability of GGA PBE functional in combination with ZORA TZP basis set for the Nb-containing coordination compounds. The geometrical, electronic, and vibrational properties of large variety of substituted Nb₆Cl ₁₂ ⁱ Y ₆ ^a clusters have been provided. One- and two-dimensional structures with a [Nb₆Cl ₁₂ ⁱ (Bipyr) _x Cl _6?x ^a ] (x?=?2 and 4) building blocks have been proposed as good and stable candidates for new coordination polydimensional materials.     

Sputtered metal cluster ions: Unimolecular decomposition and collision induced fragmentation

Cluster ions are produced by ion bombardment of thick metal targets and mass selected in a Wien filter. The unimolecular decomposition of Al _n ⁺ , Cu _n ⁺ , Mo _n ⁺ , W _n ⁺ , and Pb _n ⁺ is investigated under UHV conditions. The time evolution of the decay allows a glimpse into the cluster formation/fragmentation process. Highly excited metal cluster ions decompose mainly by evaporating single neutral atoms with rates reaching 100%. The collision induced fragmentation (CIF) of stable mass selected metal cluster ions in a low pressure Ar and O₂ gas target will be compared to the unimolecular decay.     

Fragmentation of doubly charged ammonia cations NH 3 ++ studied by the photoion-photoion coincidence (PIPICO) method

Doubly charged NH ₃ ⁺⁺ cations were produced by double photoionization of neutral ammonia molecules by using the synchrotron radiation from ACO as a photon source of variable energy in the 35–49 eV energy range. The fragmentation of NH ₃ ⁺⁺ was studied by the photoion-photoion coincidence (PIPICO) method. NH ₃ ⁺⁺ cations were produced in the \(\tilde X^1 \) A ₁ and \(\tilde B^1 \) electronic states of which the onset energies were measured at, respectively, 35.4±0.5 eV and 44.5±0.5 eV. It was shown that the NH ₃ ⁺⁺ ions, initially produced in their \(\tilde X^1 \) A ₁ state, rapidly dissociate (in less than 50 ns), into NH ₂ ⁺ + H⁺. Furthermore, the comparison with results obtained by other methods indicates that NH ₃ ⁺⁺ ions can either be long-lived (τ>10 µs) or slowly dissociating (1 µs<τ<10 µs) or rapidly dissociating (τ<50 ns), depending on their geometry and/or internal energy in their \(\tilde X^1 \) E A ₁ electronic state.     

Ab initio calculation of the vertical excitation energies of small helium cluster ions

Quantum chemical ab initio calculations have been performed for the vertical excitation energies and oscillator strengths of all low-lying electronically excited states of small helium cluster ions, He _n ⁺ ,n=2, ..., 7. The geometrical structures of the ions were fixed at the equilibrium geometries of the respective ground states, for He ₄ ⁺ and He ₅ ⁺ also one alternative structure was considered. The low-lying excited states can be classified into two categories: the electronic transition can occur either within the central He ₂ ⁺ or He ₃ ⁺ unit or from the peripheral weakly bound He atoms to this unit. The latter transitions are very weak (f≈0.001), closely spaced, with vertical excitation energies of about 5.7 eV. The He ₂ ⁺ and He ₃ ⁺ units have strong transitions at 9.93 and 5.55 eV, respectively; these transitions are only slightly blue-shifted if He ₂ ⁺ or He ₃ ⁺ are placed as “chromophores” into the centre of a larger He _n ⁺ cluster. The large difference in the vertical excitation energy of the strong transition should enable an experimental decision of the question whether the cluster ions have He ₂ ⁺ or He ₃ ⁺ cores.     

Molecular orbital calculations on transition metal complexes. Part IX

Potential energy curves for the ground and some low energy excited states of a number of complexes with a 3d ⁵ electronic configuration have been computed from INDO type SCF MO calculations. The results agree extremely well with the known ground states of the complex ions MnF ₆ ^4? , FeF ₆ ^3? , CoF ₆ ^2? , and Fe(CN) ₆ ^3? , in particular the crossover from high to low spin being obtained for changes in both central metal ion oxidation state and ligand. The calculated contraction in metal ligand distance on passing from the high spin to the low spin state is ～ 0.05 Å for each complex in very good agreement with the value indicated by pressure dependent magnetic measurements. Computed electronic transition energies involving bothd-d type and charge-transfer excitations compare favourably with observed spectroscopic values.     

Analysis of optical absorption spectra of transition metal cluster ions by the spin-polarized DV-Xα method

Optical absorption spectra of cobalt cluster ions, Co _n ⁺ , and vanadium cluster ions, V _n ⁺ , were analyzed by a theoretical calculation based on the spin-polarized DV-Xα method, and their electronic and geometric structures were obtained. Relative absorption cross section associated with each electronic transition was calculated; the calculation enables a qualitative comparison of calculated spectrum with a measured one not only in its transition energy but also in its intensity profile. This analysis shows that Co ₄ ⁺ , Co ₃ ⁺ , and V ₄ ⁺ have, respectively, a tetrahedral structure with a bond distance of 2.00Å, an equilateral triangle with a bond distance of 2.30Å, and a distorted tetrahedral structure with five bonds having a distance of 2.34 Å and one of 2.89Å. The differences in the population between majority and minority spins (spin-difference) evaluated from the electronic structure thus obtained were 2.0, 1.7, and zero per atom in Co ₃ ⁺ , Co ₄ ⁺ , and V ₄ ⁺ , respectively. These spin differences indicate a ferromagnetic and an antiferromagnetic spin-coupling in the cobalt and vanadium cluster ions, respectively.     

On the stability of Pb n m+ -clusters

The stability of multiply charged Pb _n ^m+ -clusters (n ≤ 3;m=0, 1, 2) was studied by solving exactly for the valencep-electrons a many body Hubbard-like Hamiltonian with intra- and interatomic Coulomb interactions. Particularly we obtain that Pb ₃ ²⁺ has a metastable ground state, in which Pb ₃ ²⁺ has isosceles shape (bond lengthR=3.2 Å, bond angle θ=124°) and a positive binding energyE _B =3.4 eV. The activation barrier against dissociation into Pb ₂ ⁺ + Pb⁺ is 0.13 eV, yielding a very long lifetime. This is in agreement with recent experiments [1] in which the lifetime of Pb ₃ ²⁺ was determined to be at least 10^?6 s. Comparison with self consistent Hartree-Fock calculations shows that the metastability of Pb ₃ ²⁺ is due to electronic correlations within the paramagnetic ground state.     

The electronic structure of FeO 4 2− , RuO4, RuO 4 − , RuO 4 2− and OsO4 by the HFS-DVM method

The electronic structures of FeO ₄ ^2? , RuO₄, RuO ₄ ^? , RuO ₄ ^2? and OsO₄ have been investigated using the Hartree-Fock-Slater Discrete Variational Method. The calculated ordering of the valence orbitals is 2t ₂, 1e, 2a ₁, 3t ₂ andt ₁ with thet ₁ orbital as the highest occupied. The first five charge transfer bands are assigned as:t ₁→2e(v ₁), 3t ₂→2e(v ₂),t ₁→4t ₂(v ₃), 3t ₂→4t ₂(v ₄) and 2a ₁→4t ₂(v ₅). It is suggested that ad-d transition should be observed at 1.5 eV in RuO ₄ ^? and RuO ₄ ^2? .     

Resonant two-photon ionization spectroscopy of C6H6-(SF6)1,2

Vibrationally resolved electronic spectra of heteroclusters C₆H₆-SF₆ and C₆H₆-(SF₆)₂ were studied in the spectral regions near the S₀-S₁, 0 ₀ ⁰ and 6 ₀ ¹ transitions of the benzene monomer. A nonvanishing 0 ₀ ⁰ vibrational band has been observed for C₆H₆-SF₆ with a C_3v symmetry. For both clusters we have determined the ionization potentials as well as the binding energies in the electronic ground state and the ionization state. The fragmentation of larger clusters (C₆H₆)_n(SF₆)_m is restricted to the loss of SF₆ molecules while the emission of C₆H₆ molecules have not been observed.     

Thermodynamic modeling of the reaction of polychlorinated biphenyls with sodium methoxide

Thermochemical parameters, like standard enthalpy of formation (ΔH ₂₉₈ ⁰ ), enthalpy increment from 0 to 298 K (H ₂₉₈ ⁰ - H ₀ ⁰ ), standard heat capacity (C _p298 ⁰ ) and its temperature dependence [Cp(T)], and entropy (S ₂₉₈ ⁰ ), were calculated for the gaseous methoxy derivatives formed from polychlotinated biphenyl (PCB) congeners. Thermodynamic modeling and the HSC software were used to evaluate the reactivity of PCB congeners toward sodium methoxide in DMSO, and the calculation results were compared with experimental data.     

Direct measurement of the N 2 + dissociation energy

The accuracy for the direct measurement of the dissociation energy of the N ₂ ⁺ B²Σ _u ⁺-state was significantly improved by using frequency doubled laser light, which enables the authors to excite from lowerv″-levels and additionally to calibrate the fundamental laser wavelength with an iodine cell. The obtained value is:D ₈(N ₂ ⁺ )=70248±6 cm^?1.