Mechanisms of anion formation in O2, O2/Ar and O2/Ne clusters; the role of inelastic electron scattering

Measurements are reported on the formation of negative ions in O₂, O₂/Ar and O₂/Ne clusters aimed at establishing the mechanisms of anion formation and the role of inelastic electron scattering by the cluster constituents on negative ion formation in clusters. In the case of pure O₂ clusters the main anions we detected are of two types: O^–(O₂) _n0 and (O₂) _n ^1– . The yields of O^–(O₂) _n showed maxima at 6.3, 8.0 and 14.0 eV and the data suggest O^– as their precursor; the maxima at 8 and 14 eV are due to the production of O^– via symmetry forbidden dissociative attachment processes in O₂ at these energies which become allowed in clusters. The yields of (O₂) _n ^– showed a strong maximum at near-zero energy (0.5 eV) and also at 6.3, 8 and 14 eV. With the exception of the near-zero energy resonance, the (O₂) _n ^– anions at 6.3, 8 and 14 eV are attributed to nondissociative attachment of near-zero energy secondary electrons to O₂ clusters. The slow secondary electrons result predominantly from scattering via the O ₂ ^– negative ion states of incident electrons with energies in their respective regions. Similar results were obtained for the mixed O₂/rare gas clusters except that now a feeble and distinctly structured contribution in the yields of O^–(O₂) _n , (O₂) _n ^– (and Ar(O₂) _n ^– ) was observed at energies >10 eV. These anions are believed to have the lowest negative ion states of Ar*^– (Ne*^–) as their precursors.     

Estimation of the porous structure of active carbons

Active carbons from apricot, plum, peach, and grape stones were prepared. The analysis of adsorption isotherms of benzene vapor showed that the active carbons obtained from fruit stones have highly homogeneous microporous structures withW ₀ 0.30 cm³ g^–1,E ₀ 24.5 kJ mol^–1, andx ₀ 0.42 nm, and they contain ultramicropores along with micropores.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1934–1936, October, 1995.This study was financially supported by the Russian Foundation for Basic Research (Project No. 94-03-09550).     

Molecular spectra of nitroisoxazolinones

A study is made of IR and UV spectra of N-oxides of nitroisoxazolinones, and of derivatives of isoxazolidine and isoxazolizidine. Absorption bands are related to valence vibrations of N-O in the NO₂ group; in conjugated systems (in N-oxides of nitroisoxazolines) _s and _as are equal to 1310 and 1510 cm^–1, in nonconjugated systems (in nitroisoxazolidines) 1360 and 1560 cm^–1, respectively. Frequencies of N-O bond vibrations in N-oxides appear in the region 830–870 cm^–1, of the O-N-O fragment in isoxazolidines and isoxazolizidines in the 1010–1060 cm^–1 region. Measurements are made of total intensities of N-O valence vibrations in the NO₂ group in N-oxides of nitroisoxazolines and nitroisoxazolizidines, as well as of C=N valence vibrations in N-oxides of nitroisoxazolines.     

The interaction of dansyl amino acids with bovine serum albumin

The interaction of 5-dimethylaminonaphthalene-1-sulfonyl (DNS or dansyl) amino acids with bovine serum albumin (BSA) was investigated by means of fluorescence measurements. Fluorometric titrations revealed that BSA has one high affinity site (binding constant,K _a=10⁵10⁶ M^–1), and other sites of lower affinity (K _a=10³10⁴ M^–1) for the probes. Static excitation and emission spectra, lifetimes, time resolved emission spectra, and anisotropy data indicated that the binding is stabilized mainly through fixation by the high affinity binding site. The binding constant significantly decreased with the increase of the spacer distance between the dansyl and anionic groups of the probe molecule. This observation was explained by considering the change of the electrostatic interaction between the anionic group of the probe and a cationic residue in the vicinity of the site.     

Synthesis,complexing properties and molecular modelling of open chain receptors of barbiturates derived from 2,6-diamino pyridine

Three new derivatives of 2,6-diacyldiaminopyridine are reported. NMR shift titrations were performed in CDCl₃ with barbiturates. The diamide1 affords a greater complexation energy (–13.00 kJ mol^–1) with bemegride than the dithioamide2 (–9.15 kJ mol^–1). This result, unexpected on the basis of the proton acidities, is explained by the great torsion energy induced in2 by the bulky sulfur atom. Compounds3 and4 present unusual four and five H-bond features with barbital and relatively weak complexation energies (–9.53 and –16.34 kJ mol^–1, respectively). Molecular mechanics indicates that ligand4 displays a helical secondary structure which is disrupted by complexation. Calculations of the H-bond energies (E _calc.) of the intermolecular assemblies with barbital or phenobarbital and other host-guest complexes given in the literature give a good correlation (r=0.98) with experimental values: E _calc.=1.07 G _a–42.0. Limitations of this relation are discussed.     

Sol-Gel Derived Nanocomposites and Nanoporous Oxide Powders and Related Coatings for the Reversible Chemisorption of Hydrogen Sulfide

Two types of nanocomposites and nanoporous powders and related coatings were prepared by the sol-gel route. These silica-based materials contain dispersed reactive oxides, ZnO and ZnCr₂O₄, respectively. Experiments evidenced their ability of reversible chemisorption of H₂S as ZnS. Their attractive porous characteristics (small pore size 2–2.5 nm, high specific surface area 900–1100 m²· g^–1, high porosity 50–60%) are not significantly modified during the successive treatments of H₂S chemisorption and oxide regeneration. These preliminary results encourage to pursue this study which aims at the preparation of nanofilters for the desulfurization of gas mixtures.     

Conductivity of Aqueous Solutions of Low-Molecular Chitosan

Solutions of chitosan with molecular weight (MW) of 20000, 9600, and 3700 Da are studied conductimetrically and viscosimetrically. The dependence of solution conductivity on the chitosan concentration begins to deviate from linearity simultaneously with an abrupt increase in the solution viscosity starting from concentrations of 20–30 g l^–1. The fraction of free counterions (Cl^–, CH₃COO^–) in the 0.1 g-equiv l^–1 chitosan solutions significantly depends on the sample's MW. The charge is transferred in solutions predominantly by chloride and acetate ions, with the high-MW cation barely contributing to conduction.     

The kinetics of the reaction of iodine with hydrazine as studied by pulse radiolysis

Pulse radiolysis was utilized to study the iodine — hydrazine reaction in aqueous solutions of pH3 to 7, at I^– concentrations of 0.02 to 0.34M, and a constant ionic strength of 0.35M. The reaction rate was found to be proportional to [H⁺]^–1 and [I^–]^–1. Experimental results support the assumption that the rate-determining step is the reaction of I₂ with N₂H₄ with a rate constant K1.2×10⁷ M^–1s^–1.     

Triplet states of humic acids studied by laser flash photolysis using different excitation wavelengths

The spectra and kinetics of short-lived intermediates formed from aqueous (0.1 N NaOH) solutions of the natural mixture of humic and fulvic acids (HFA) were studied by laser flash photolysis using excitation wavelengths of 337, 390, 470, and 520 nm. Laser photolysis of HFA with light of 520 and 470 nm results in the formation of triplet excited states (T_HFA) characterized by the broad absorption spectrum with a maximum near 630 nm and lifetimes of 0.15 ms in deoxygenated solutions. The formation of two types of T_HFA with lifetimes of 0.1 and 2 ms and absorption spectra with maxima at 570 nm is observed under photolysis with light of 337 and 390 nm. The estimation of quantum yields of T_HFA gives 1 and 0.3% under photolysis with excitation wavelengths of 337 and 520 nm, respectively. The rate constants of T_HFA quenching by molecular oxygen are equal to (7—8)·10⁸ L mol^–1 s^–1.     

Ab-initio calculations on small hydrides including electron correlation

The ground state energies of CH ₃ ⁺ , CH₃, and CH ₃ ^– are calculated both in the SCF (near Hartree-Fock) approximation and in the IEPA-PNO scheme including correlation energy. Due to a more appropriate choice of the basis, our SCF-values for CH ₃ ^– are substantially better than previously published ones. Both CH ₃ ⁺ and CH₃ are planar whereas the equilibrium bond angles in CH ₃ ^– are nearly tetrahedral. The inversion barrier of CH ₃ ^– is 2kcal/mol. The force constants of the out-of-plane bending modes are changed by correlation in the case of CH₃ from 0.03–1.8 mdyn/Å. The localized MO's that correspond to the CH-bonds are bent in the non-equilibrium geometries. The dependence of the different pair correlation contributions on the angle that describes out-of-plane deformation is analyzed. The electron affinity of CH₃ is 0.3 eV. Finally the Pariser-Parr disproportionation reaction is analyzed in the light of the present results. Changes in correlation energy for this reaction amount to less than 1 eV.     

Kinetic and EPR studies on radical polymerization. Radical polymerization of di-2[2-(2-methoxyethoxy)ethoxy]ethyl itaconate

The polymerization of di-2[2-(2-methoxyethoxy)ethoxy]ethyl itaconate (1) with dimethyl 2,2-azobisisobutyrate (2) was studied, in benzene, kinetically and spectroscopically with the electron paramagnetic resonance (EPR) method. The polymerization rate (R _p) at 50°C is given by the equation:R _p=k[2]^0.48 [1]^2.4. The overall activation energy of polymerization was calculated to be 34 kJ·mol^–1. From an EPR study, the polymerization system was found to involve EPR-observable propagating polymer radicals of 1 under the actual polymerization conditions. Using the polymer radical concentration, the rate constants of propagation (k _p) and termination (k _t) were determined. With increasing monomer concentration,k _p(1.54.3 L·mol^–1·s^–1 at 50°C) increases andk _t (1.0·10⁴4.2·10⁴ L·mol^–1·s^–1 at 50°C) decreases, which seems responsible for the high dependence ofR _p on the monomer concentration. The activation energies of propagation and termination were calculated to be 11 kJ·mol^–1 and 84 kJ·mol^–1, respectively. For the copolymerization of 1(M ₁) and styrene (M ₂) at 50°C in benzene the following copolymerization parameters were found:r ₁=0.2,r ₂=0.53, Q₁=0.57, ande ₁=+0.7.     

Concentrations of Active Species in the Flowing Afterglow of a Nitrogen Microwave Plasma

Measurements of nitrogen atom density, by means of NO chemical titration, along with an evaluation of the densities of some excited species N ₂ (B, v=11), N ₂ (B, v=2), N ₂ (C, v=0), and N ₂ ⁺ (B,v=0), by means of a spectroscopic study of some bands of dinitrogen, are achieved along the flowing afterglow of a dinitrogen microwave plasma (2450 MHz) for several pressures. The concentrations obtained are in the following range: [N]10 ⁺¹⁵ , [N ₂ (B, 2)]10 ⁺⁹ –10 ⁺¹⁰ , [N ₂ (B, 11)]10 ⁺⁸ –10 ⁺⁹ , [N ₂ (C, 0)]10 ⁺⁶ –10 ⁺⁷ , [N ₂ ⁺ (B,0)]10 ⁺⁶ -10 ⁺⁸ (cm^-3). From a kinetic study of the formation and decay of excited and charged species, an estimation of N ₂ (A, v), N ₂ (X, v, and N ₂ ⁺ (X) densities can be derived: [N ₂ (A, v)]10 ⁺¹² , [N ₂ (X, v6)]10 ⁺¹⁵ –10 ⁺¹⁶ , [N ₂ (X, v12)]10 ⁺¹⁴ –10 ⁺¹⁵ , [N ₂ ⁺ (X)]10 ⁺¹⁰ (cm ^-3 ).     

Infrared spectral analysis during the thermal decomposition of pure and irradiated crystalline NH4ClO4

Variable temperature /303–553 K/ IR spectroscopic studies are made during thermal decomposition of pure and -treated ammonium perchlorate /AP/. Decomposition is enhanced by radiation or in the presence of an additive /Gd₂O₃/. Intensity of the stretching /1100 cm^–1/ and bending /625 cm^–1/ frequencies of ClO ₄ ^– decrease on heating the KBr matrix even below 360 K. Above this temperature, a broad band develops over 480–510 cm^–1 in the pure and -treated AP which is attributed to ClO ₃ ^– /₄/.     

The CO2 Reforming of Natural Gas in a Pulsed Corona Discharge Reactor

The conversion of CO ₂ and (CH ₄+CO ₂ ) mixtures to CO, at room temperature and atmospheric pressure conditions, in pulsed corona discharges, was investigated. Conversion of pure CO ₂ was 16.8% at 10 cm ³ -min ^–1 flow rate, which corresponds to 75 mol-min ^–1 rate of conversion. The CO ₂ conversion was improved to 38% (85 mol-min ^–1 by feeding the reactor with CH ₄+CO ₂ gas mixture (1:1 ratio), simultaneously with CH ₄ conversion of 46% (102.7 mol-min ^–1 ) at 10 cm ³ -min ^–1 flow rate of feed gases and 9 W power conditions. Rate of CO production is increased from 110 to 180 mol-min ^–1 with the variation of feed gas (CH ₄+CO ₂ mixture, 1:1 ratio) flow rate from 10 to 40 cm ³ -min ^–1 at 9W, which corresponds to energy efficiency of 2.5 to 4.1%. Highest energy yield of 25 g/kWh for CH ₄ conversion, 29 g/kWh for CO ₂ conversion, and 33 g/kWh for CO production were achieved.     

Tail-end purification of americium from plutonium loading effluents using a mixture of octyl (phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide and tri-N-butyl phosphate

The tail-end purification of Am from Pu loading effluents in 7.5M HNO₃ containing 160 mg l^–1 Am and 1.2 mg l^–1 Pu has been carried out. With 0.2M CMPO+1.2M TBP in dodecane as the extractant and stripping by 0.04M HNO₃+0.05M NaNO₂, the Pu level is brought down to 31.2 g l^–1. When the acidity was reduced to 4.2M HNO₃, one contact with 20% TLA/dodecane and subsequent extraction by a mixture of CMPO and TBP and stripping with 0.04M HNO₃+0.05M NaNO₂ gave Am samples without any detectable amounts of Pu. The recovery of Am was 90% by the first procedure and 98% by the second one.     

Crystal and molecular structure of the simple cation-radical salt ethylenedithiopropylenedithiotetrathiafulvalene trichloromercurate (EPT)HgCl3

The new cation-radical salt (EPT)HgCl₃ is prepared. Its structure and electrical conductivity are studied. The crystal structure of (EPT)HgCl₃ contains (EPT)⁺ in the chair conformation and trigonal planar HgCl₃ ^– packed into organic and inorganic layers alternating along thea axis. Shortened intermolecular contacts join HgCl₃ ^– into infinite chains along the c axis (Hg...Cl, 3.289 and 3.387 Å), form stacks (S...S, 3.536 and 3.597 Å) and layers (S...S, 3.427–3.498 Å) of EPT⁺ cation-radicals, and create cation-anion interactions between neighboring layers in the crystal (Cl...S, 3.396–3.521 Å, Cl...C, 3.360 Å). The configuration of the bonds around Hg in HgCl₃ ^– is distorted trigonal planar: Hg-Cl, 2.342(3)–2.449(3) Å, Cl-Hg-Cl, 110.7(1)–137.4(1). The Hg atom lies out of the plane of the Cl atoms by 0.015 Å. The conductivity of (EPT)HgCl₃ at 20°C is ₃₀₀ 5·10^–2 (·cm)^–1. The dependence of conductivity on temperature is semiconducting in nature.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2055–2061, September, 1991.     

Estimated ionicB-coefficients from NMR measurements in aqueous electrolyte solutions

¹⁷O-NMR spin-lattice relaxation timesT ₁ of D₂O molecules were measured at 5–85°C in D₂O solutions of alkali metal halides (LiClCsCl, KBr, and KI), DCl, KOD, Ph₄PCl, NaPh₄B, and tetraalkylammonium bromides (Me₄NBrAm₄NBr) in the concentration range 0.1–1.4 mol-kg^–1 TheB-coefficients of the electrolytes obtained from the concentration dependence of relaxation ratesR ₁=1/T₁ were divided into the ionicB-coefficients by three methods: (i) the assumption ofB (K⁺)=B(Cl^–), (ii) the assumption ofB(Ph₄P⁺)=B(Ph₄B^–), and (iii) the use ofB(Br^–) obtained from a series ofB(R₄NBr). It was found that Methods (ii) and (iii) resulted in an abnormal temperature dependence of theB-coefficients of alkali metal ions and a negative values of rotational correlation times _c at lower temperatures for hydroxide and halide ions. These results suggest that the methods based on the van der Waals volume are not adequate for the ionic separation of NMRB-coefficients. From the analysis using the assumption ofB(K⁺)=B(Cl^–), it was found that D₃O⁺, OD^–, and Me₄N⁺ ions are the intermediates between structure makers and breakers, and that the hydrophobicity of phenyl groups is weaker than that of alkyl groups due to the interactions between water molecules and -electrons in phenyl groups.     

Gamma radiolysis of Methyl Red solution and reaction induced by γ-irradiated NaCl in Methyl Red

The -radiolysis of Methyl Red solution in HCl medium at pH=2 has been studied along with energy transfer reaction brought about byF and hole centers of -irradiated NaCl. The G-values for degradation of the azo dye indicator by radiolysis and -irradiated salt were determined as 9·10^–1 and 4.8·10^–3, respectively. The kinetic rate constants (k) of degradation are evaluated as 2·10^–5 rad^–1 in the case of direct radiolysis, while for the irradiated salt it is 2·10^–7 rad^–1. The extent of degradation by direct -radiolysis is 100–200 times greater as compared to that by the -irradiated salt. The same mechanism is proposed for radiolysis as well as the reaction induced by -irradiated sodium chloride.     

Spectroscopy Challenge 4

The effect of the Prandtl number (Pr) and the Reynolds number (Re) on the behaviour of weak laminar axisymmetric and plane fountains has been studied using dimensional and scaling analyses and direct numerical simulation. For Fr 1.0 and assuming viscous effects are important, the analysis shows that for both the axisymmetric and plane fountains, y_mFrRe^–1/2, where Fr is the Froude number defined at the fountain source and y_m is the non-dimensionalized fountain height. These scalings are also valid for the non-dimensionalized fountain width. The analyses also shows _msFr², where _ms is the non-dimensionalized time scale for the fountain flow in the fountain core to reach steady state, and using this time scale y_TFr(RePr)^–1/2, where y_T is the non-dimensionalized thickness of the temperature layer on the symmetry axis over which the fountain fluid temperature changes from the inlet value to that of the ambient fluid. All these scalings have been quantified by the direct numerical simulations, hence confirming in certain ranges the phenomenological scaling obtained in this paper. The financial supports from the National Natural Science Foundation (grant numbers 19872059 and 10262003) and Yunnan Province of the People's Republic of China to W. Lin and the Australian Research Council are gratefully acknowledged.     

Comprehensive Thermodynamic Model Applicable to Highly Acidic to Basic Conditions for Isosaccharinate Reactions with Ca(II) and Np(IV)

Isosaccharinate (ISA^–), a degradation product of cellulose codisposed in low-level nuclear wastes, is expected to be one of the dominant complexing ligands for radionuclides, especially tetravalent actinides. This paper presents a comprehensive thermodynamic model for isosaccharinate reactions with Ca(II) and Np(IV). The model is valid for a wide range of pH values (2–14), ISA^– concentrations (ranging up to 0.1 m), and ionic strengths (ranging up to 6.54 m), and is based on (1) NMR investigations of HISA(aq) (-D-isosaccharinic acid) and ISL(aq) [dehydration product of HISA(aq)], and the solubility of Ca(ISA)₂(c) as a function of pH and concentrations of Ca and ISA^–; (2) NpO₂(am) solubility in a wide range of pH values (2–14) and total ISA concentrations of 0.0016 and 0.008 m and at fixed pH values of approximately 5 and 12 with total ISA concentrations ranging from 0.0001 to 0.1 m; and (3) solvent extraction of Np-ISA solutions, containing fixed NaClO₄ concentrations ranging from 0.103 to 6.54 m and at fixed pC _H+ values ranging from 1.5 to 1.9, with dibenzoylmethane. Pitzer's ion-interaction approach was used to interpret the data. The different aqueous species required to explain these data included HISA(aq), ISL(aq), Ca(ISA)⁺, Np(OH)₃(ISA)(aq), Np(OH)₃(ISA)₂ ^–, Np(OH)₄(ISA)^–, and Np(OH)₄(ISA)₂ ^2–. The values of equilibrium constants for reactions involving these species and determined from these data provided close agreements between the observed and predicted concentrations in all of the systems investigated in this study and those reported previously.