Ab initio study of small He cluster ions He n + ,n=2, 3, 4, 5, and low-lying Rydberg states of He4

SCF and CEPA calculations are applied to study the structure of small He cluster ions, He _n ⁺ ,n=2, 3, 4, 5 and some low-lying Rydberg states of He₄. The effect of electron correlation upon the equilibrium structures and binding energies is discussed. He ₃ ⁺ has a linear symmetric equilibrium geometry with a bond length of 2.35a ₀ and a binding energyD _e =0.165 eV with respect to He ₂ ⁺ +He (experimentally:D ₀=0.17 eV which corresponds toD _e ≈0.20 eV). He ₄ ⁺ is a very floppy molecular ion with several energetically very similar geometrical configurations. Our CEPA calculations yield a T-shaped form with a He ₃ ⁺ centre (R _e = 2.35a ₀) and one inductively bound He atom (4.39a ₀ from the central He atom of He ₃ ⁺ ) as equilibrium structure. Its binding energy with respect to He ₃ ⁺ +He is 0.031 eV. A linear symmetric configuration consisting of a He ₂ ⁺ centre with a bond length of 2.10a ₀ and two inductively bound He atoms (4.20a ₀ from the centre of He ₂ ⁺ ) is only 0.02–0.03 eV higher in energy. We expect that in larger He cluster ions structures with He ₂ ⁺ and He ₃ ⁺ centres andn?2 orn?3 inductively bound He atoms have nearly the same energies. In He₄ a low-lying metastable Rydberg state (³ Π symmetry for linear He ₄ ^* ,³ B ₁ for the T-shaped form) exists which is slightly stronger bound with respect to He ₃ ^* +He than the corresponding ion.     

Octacoordination of the nitrogen atom in M4NO 4 + systems (M = Li, Na, K)

The electronic and geometric structures of M₄NO ₄ ⁺ compounds (M = Li, Na, K) in classical and nonclassical isomeric forms were studied by the ab initio (MP2(full)/6-311+G**) and density functional theory (B3LYP/6-311+G**) methods. For all M atoms, structurally stable nonclassical isomers were found with octacoordinated nitrogen atoms and tetracoordinated oxygen atoms. For Li₄NO ₄ ⁺ , the classical structure with the tetracoordinated nitrogen atom is energetically more stable, whereas nonclassical structures with the octacoordinated nitrogen center are more stable for Na₄NO ₄ ⁺ and K₄NO ₄ ⁺ .     

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.     

Calorimetric determination of the standard enthalpy of the first ionization of aqueous sulfur dioxide or ‘sulfurous acid’ at 25°C

Previous investigations of the first ionization of aqueous sulfur dioxide or ‘sulfurous acid’ have led to ΔH ₁ ⁰ values ranging from ?15 to ?24.5 kJ-mol^?1. To help with selection of a ‘best’ value for this enthalpy of ionization we have made calorimetric measurements of enthalpies associated with adding dilute perchloric acid to dilute aqueous sulfur dioxide and sodium bisulfite. Results have led to ΔH ₁ ⁰ =?17.4₀ kJ-mol^?1, which we have combined with K₁=0.0139 and the related ΔG ₁ ⁰ =10.60 kJ-mol^?1 to obtain ΔS ₁ ⁰ =?93.₉ J-K^?1-mol^?1 for the first ionization, all referring to 25°C.     

Reactivity of positively charged cobalt cluster ions with CH4, N2, H2, C2H4, and C2H2

Reactivity of positively charged cobalt cluster ions (Co _n ⁺ ,n=2?22), produce by laser vaporization, with various gas samples (CH₄, N₂, H₂, C₂H₄, and C₂H₂) were systematically investigated by using a fast-flow reactor. The reactivity of Co _n ⁺ with the various gas samples is qualitatively consistent with the adsorption rate of the gas to cobalt metal surfaces. Co _n ⁺ highly reacts with C₂H₂ as characterized by the adsorption rate to metal surfaces, and it indicates no size dependence. In contrast, the reactions of Co _n ⁺ with the other gas samples indicate a similar cluster size dependence; atn=4, 5, and 10?15, Co _n ⁺ highly reacts. The difference can be explained by the amount of the activation energy for chemisorption reaction. Compared with neutral cobalt clusters, the size dependence is almost similar except for Co ₄ ⁺ and Co ₅ ⁺ . The reactivity enhancement of Co ₄ ⁺ and Co ₅ ⁺ indicates that the cobalt cluster ions are presumed to have an active site for chemisorption atn=4 and 5, induced by the influence of positive charge.     

Extraction of nitric acid,technetium and palladium by bidentate carbamoylphosphonates

The extraction of HNO₃, TcO ₄ ^? , and Pd by solutions of dibutyl N,N-diethylcarbamoylmethylenephosphonate (DBDECMP) and dibutyl N,N-diethylcarbamoylphosphonate (DBDECP) in CCl₄ has been studied. At low aqueous acidities, HNO₃ is extracted by both extractants (S) as HNO₃·S and HNO₃·S₂, at >1M HNO₃ only HNO₃·S is formed. The distribution of TcO ₄ ^? and Pd(II) is nearly independent of HNO₃ concentration. A second power dependence on extractant concentration was found for the extraction of Pd(II) by DBDECMP and TcO ₄ ^? by DBDECP, and a 4th power dependence for TcO ₄ ^? -DBDECMP.     

Description of Am(III) microamount extraction in the presence of lanthanide macroamounts

On the basis of distribution dependences, an analysis of the effect of the macrocomponent (lanthanide) on the extraction of the microcomponent (americium) by benzyl-dialkylamines and benzyltrialkylammonium salts has been made. Assuming the validity of D_Ln=f(c _Ln ^o ) and D_Am=f(c _Ln ^o ), the power function of the general expression log D=logP-Qlog c _Ln ^o has been calculated, the constants have been determination of the equation applying to individual extraction systems and their physical and chemical characteristics have been discussed.     

Solvation numbers and hydration constant for thorium(IV) in ethanol-water medium

The solvation number and hydration constant of Th⁴⁺ in ethanol-water medium were determined at 25°C using UV-spectral and electrochemical measurements. A solvate formation equilibrium is demonstrated and characterized. Three molecules of ethanol (S) can bond to the metal cation with strengths comparable to that for H₂O to form ThS₃(H₂O) ₃ ⁴⁺ Formation of thorium monochelate with lawsone (2-hydroxy-1,4-naphthoquinone) eliminates bonding with alcohol molecules. The dissociation constant of the chelating agent_sK_a and the formation contant of the monochelated metal ion_sK _f ^* that are essentially independent of the solution composition are evaluated. Hydration titrations involving thorium-lawsone monochelate are performed and the data obtained from the changes of pH with solvent composition are analyzed. The solution independent constant,_sK _f ^* for thorium-lawsone complex formation in mixed aqueous ethanol is given by $$log_s K_f * = vpK_a + log_s K_h - log[LH] - vpH + 3logv$$ where vpK_a is the dissociation constant of the chelating agent LH in the solvent system of ν volume fraction of water and_sK_h is the solution-independent hydration constant of thorium (IV) in the solvent system. Log-values for the constants_sK_h,_sK _f ^* and_sK _a ^* are found to be 7.8±0.02, 11.38±0.04 and ?0.753, respectively.     

Extraction-photometric selective determination of trace perchlorates in potable waters

A method is proposed for the selective photometry determination of perchlorates in potable water with a detection limit of 2×10^?3 mg/L is proposed based on the extraction of its ion pair with the astrafloxin cation and absorbance measurements at 540 nm. The following ratios of matrix ions are acceptable (in parentheses): ClO^?, ClO ₂ ^? , ClO ₃ ^? , BrO ₃ ^? (500); I^? (1000); IO ₃ ^? (7000); HCO ₃ ^? , Cl^?,SO ₄ ^2? , NO ₃ ^? , Br^?, Na⁺, K⁺, Ca²⁺, Mg²⁺ (10000). The relative error of determination for ClO ₄ ^? is 20% in the range 4 × 10^-3-1 × 10^?2 mg/L and 10% in the range 1 × 10^-2–5 × 10^?2 mg/L.     

Theoretical Investigation on the Interaction of C2H Radical with Small Gold Clusters Au n 0/− (n = 1–4)

A density-functional theory investigation on the interactions between C₂H radical and small gold clusters Au _n ^0/? (n = 1–4) has been performed. The calculated results predict that C₂H radical inclines to interact with small gold clusters Au _n ^0/? (n = 1–4) as an integrity in the most stable structures of C₂HAu _n ^0/? (n = 1–4). The Au _n ^0/? (n = 1–4) clusters retain their structural integrity as units in the ground states of C₂HAu _n ^0/? (n = 1–4). The stretching vibrational frequencies of C≡C and C–H in the ground states of C₂HAu _n ^? (n = 1–4) are decreased compared with those of the C₂H radical due to the interaction between the Au _n ^0/? clusters and C₂H radical. Smaller red shifts in the C≡C and C–H stretching bands of C₂HAu _n ^? occur with an increase in n. The photoelectron spectra of the most stable structures of C₂HAu _n ^? (n = 1–4) have been simulated to aid their future experimental characterizations. The current study provides further insight into the interaction between C₂H radicals and gold clusters, which may lead to exploitation of the high activity of gold nanocrystals.     

Gemischt quantenmechanisch-statistische Modellrechnungen nach der Einzentrenmethode an Wasserstoffverbindungen tetraedrischer Symmetrie von Elementen der III., IV. und V. Hauptgruppe

Using a one-center-method, treating the inner shells statistically, the valence-shell, however, by quantum mechanics, the equilibrium internuclear distances and total molecular energies have been computed for CH₄, SiH₄, GeH₄, SnH₄, PbH₄, BH ₄ ^? , AlH ₄ ^? , GaH ₄ ^? , InH ₄ ^? , TlH ₄ ^? , NH ₄ ⁺ , PH ₄ ⁺ , AsH ₄ ⁺ , SbH ₄ ⁺ , and BiH ₄ ⁺ . The results are in good agreement with experimental data as well as with theoretical values.     

Diffusion and Ion Association in Concentrated Solutions of Aqueous Lithium, Sodium, and Potassium Sulfates

Taylor dispersion is used to measure mutual diffusion coefficients for aqueous Li₂SO₄ solutions at concentrations from 0.09 to 2.62 mol-dm^-3 at 25°C. The Li₂SO₄ results and previously reported diffusion coefficients for aqueous Na₂SO₄ and K₂SO₄ are compared with predictions made by treating the limiting electrolyte diffusion coefficients as reference values and applying corrections for nonideal solution behavior, ionic hydration, and viscosity changes as the concentration is raised. Good agreement is obtained if the M⁺ + SO ₄ ^2- ? MSO ₄ ^- (M = Li, Na, K) association equilibria are included in the analysis. Extents of formation of the MSO ₄ ^- ion pairs are evaluated by fitting Pitzer's mixed electrolyte equations for aqueous M⁺–MSO ₄ ^- –SO ₄ ^2- ions to osmotic coefficient data. Diffusion coefficients for hypothetical solutions of the completely dissociated M₂SO₄ electrolytes are calculated to illustrate the effects of ion association on diffusion. Association of the M⁺ and SO ₄ ^2- ions increases the overall mobility and thermodynamic driving forces for their diffusion.     

Amino acid hydration in aqueous ammoniu chloride and sodium chloride solutions

Partial volumes $\bar V^0$ of amino acids in aqueous NH₄Cl and NaCl solutions are discussed. The salts have different effects on water structure. The contributions of the charged NH ₃ ⁺ and COO^? groups of amino acids are found. Structural characteristics of hydrated complexes are calculated: partial volumes of water inside and outside the hydration sphere and hydration numbers. The same value of $\bar V^0$ (NH ₃ ⁺ , COO^?) is achieved at a higher NH₄Cl concentration. The two salt systems with the same $\bar V^0$ (NH ₃ ⁺ , COO^?) have similar values of the partial volumes of water and hydration numbers.     

Studies on the equilibrium uptake of some anions on a mixed and doped hydrous oxide

A mixed hydrous Fe(III)?Zr(IV) exhibits enhanced adsorption of anions in comparison to its constituent oxides. The uptake has been observed at pH 2.0, as a function of initial salt concentration and the product shows specific affinity for Cl^?, SO ₄ ^2? and PO ₄ ^3? ions. Doping the mixed oxide with Sn(II) improves its sorption capability for halide ions, while no significant enhancement is observed in the case of polyvalent anions.     

Zur Elektronenstruktur von metallorganischen Komplexen der f-elemente

The temperature dependence of the magnetic susceptibility of Uranocene ((C₈H₈)₂U(IV)) between 1.25 and 298 K has been measured for the first time and the results correlated with a systematic study of the crystal field splitting. Independent estimates of the three crystal field parameters B ₂ ⁰ , B ₄ ⁰ and B ₆ ⁰ were obtained by adopting the purely electrostatic approach, the angularoverlap-model and the MHW-MO-method. Subsequently the crystal field splitting pattern was calculated by a simultaneous diagonalisation of the complete f ²-matrix. Assuming rigorous D _8h-crystal field symmetry, a crystal field splitting pattern involving a singlet ground state and a low lying first excited doublet state (ΔE=17cm^?1, ¦ΔJ₂¦ = 1) gives the best agreement with both the MO-results and the experimental findings. The experimental l/χ-vs-T-curve is reproduced to a good approximation by a calculation employing the optimal parameter set: B ₂ ⁰ = ?5610, B ₄ ⁰ = ?1426,B ₆ ⁰ = ?730cm^?1. A crystal field of slightly lowered symmetry having a significantly split doublet ground state and hence positive B ₂ ⁰ -values cannot be completely ruled out.     

Molecular structure of a water-polyethylene glycol-KOH system, according to densitometry and viscometry data

The dynamic viscosity and density of a water-polyethylene glycol-KOH system are measured at temperatures of 293.15 to 323.15 K in concentrations ranging from 0.00001 and 0.001 (mole fractions). The activation parameters of viscous flow (ΔG _η ^≠ , ΔH _η ^≠ , and ΔS _η ^≠ ), structural temperature (T ₀), the partial molar volume of polyethylene glycol (PEG) in solution $\left( {\tilde V} \right)$ , intrinsic viscosity([η]), and the Huggins constant (K _H), are calculated. It is found that PEG has a structuring effect on water in water-PEG and water-PEG-KOH systems, with the PEG structuring effect in the latter being somewhat attenuated by the destructuring influence of KOH.     

FTMS studies of sputtered metal cluster ions (IV): size-selective effects in the chemistry of Fe n + with NH3 and Pd n + with D2 or C2H4

Fe _n ⁺ and Pd _n ⁺ clusters up ton=19 andn=25, respectively, are produced in an external ion source by sputtering of the respective metal foils with Xe⁺ primary ions at 20 keV. They are transferred to the ICR cell of a home-built Fourier transform mass spectrometer, where they are thermalized to nearly room temperature and stored for several tens of seconds. During this time, their reactions with a gas leaked in at low level are studied. Thus in the presence of ammonia, most Fe _n ⁺ clusters react by simply adsorbing intact NH₃ molecules. Only Fe ₄ ⁺ ions show dehydrogenation/adsorption to Fe₄(NH) _m ⁺ intermediates (m=1, 2) that in a complex scheme go on adsorbing complete NH₃ units. To clarify the reaction scheme, one has to isolate each species in the ion cell, which often requires the ejection of ions very close in mass. This led to the development of a special isolation technique that avoids the use of isotopically pure metal samples. Pd _n ⁺ cluster ions (n=2...9) dehydrogenate C₂H₄ in general to yield Pd _n (C₂H₂)⁺, yet Pd ₆ ⁺ appear totally unreactive. Towards D₂, Pd ₇ ⁺ ions seem inert, whereas Pd ₈ ⁺ adsorb up to two molecules.     

Shell correction study of fission of doubly charged silver clusters

Fission of doubly charged silver clusters is investigated by the method of shell corrections. The following fission events are considered: Ag ₂₂ ²⁺ → Ag _n ⁺ + Ag _{22 ?n} ⁺ , (n=11, 10, 9, 8); Ag ₂₁ ²⁺ → Ag _n ⁺ + Ag _{21 ?n} ⁺ , (n=10, 9, 8, 7); Ag ₁₈ ²⁺ → Ag _n ⁺ + Ag _{18 ?n} ⁺ , (n=9, 8, 7, 6). It is found that the shell correction energy is comparable to or larger than the deformation energy of the liquid drop. Threshold energies for the fission events are calculated and compared with the experimental abundance spectra obtained by Katakuse et al. (1990). Correspondence between the calculated threshold energies with the shell corrections and the experimental abundance is very good, showing products from lower threshold fission channels yield more abundance. The threshold energies without the shell corrections are almost constant irrespective of the fission channels and cannot explain the experimental abundance. Abundance of some products are too small to be accounted for only by the threshold energies. The low abundance of those products may be explained by the presence of competing fission channels that have similar minimal energy paths. It is found in fission of Ag ₁₈ ²⁺ that the shell correction overwhelms the Coulomb energy and the fission channel to Ag₈ + Ag ₁₀ ²⁺ is preferred over the fission channel to Ag ₈ ⁺ + Ag ₁₀ ⁺ .