Acoustical and Viscometric Studies of CdCl2 and KCl in Aqueous-Acetone Co-Solvent Between 25 and 45°C

Abstract

Ultrasonic velocity of CdCl₂ and KCl in co-solvent of Acetone and Water is measured at different concentrations from 298.15 K to 318.15 K using single crystal interferometer; operating at frequency of 2 MHz. Various acoustical parameters such as adiabatic compressibility (β_s), specific impedance (Z), apparent molar compressibility (Ø_K), relative association (R _A), Rao's molar sound function (R), molar compressibility (W), free volume (V _f) have been calculated. Results throw light on the solute-solvent and solute-solute interactions. Effect of temperature variation on these interactions has also been discussed.     

Static dipole and quadrupole polarizabilities of alkaline earth atoms

Static dipole and quadrupole polarizability (α_d and α_q, respectively) values of coupled Hartree–Fock quality have been calculated for the alkaline earth atoms Be(2s), Mg(3s), Ca(4s), and Sr(5s) using a method based on the many-body perturbation theory. The present values of α_d and α_q for Be and α_d for Mg are in excellent agreement with the other available results of similar accuracy. The CHF calculations of α_d for Sr and α_q for Mg, Ca, and Sr are being reported for the first time.     

Theory of helicenic hydrocarbons. Part 2: Chemical formulas

The formulas C _n H _s (n; s) for helicenic hydrocarbons are treated. The restrictions onn ands are specified comprehensively in terms of inequalities. General expressions are given for the C _n H _s formulas of extremal helicenes and some of their subclasses: circumextremal- and circular helicenes. Sequences of formulas for extremal helicenes, viz. (n ₀; s₀), (n ₁; s₁), ..., (n _k; s_k), ..., are defined. Here (n ₀;s ₀) is said to represent ground-form helicenes, while (n _k; s_k) for k > 0 pertain to higher members. A higher member with the formula (n _k; s_k) is an extremal helicene which can be obtained byk-fold complete sedimentation of a ground form. This process corresponds to circumscribing of benzenoids. A formula index, viz.x as a function ofn ands, distinguishes different classes of helicenes and can be used to identify the formulas for ground forms and higher members. The possible C _n H _s formulas for helicenes and their indices are tabulated. Finally the numbers of edges in C _n H _s isomers are discussed.     

Acoustical and excess thermodynamic studies of mixtures of 2-pyrrolidone with 1,3-propanediol and water as well as 1,3-propanediol with water at 308.15 K

The density (ρ), viscosity (η) and ultrasonic velocity (u) of three mixtures consisting of 2- pyrrolidone with 1,3-propanediol (PD) and water and also of PD and water have been measured as a function of mole fraction at 308.15 K. The experimentally collected data has been used to calculate the excess molar volume (V^E), deviation in viscosity (Δη), deviation in ultrasonic velocity (Δu), isentropic compressibility (κ_s), deviation in isentropic compressibility (Δκ_s) and excess Gibbs free energy of activation (ΔG*^E). The Redlich–Kister polynomial equation has been used to fit the derived parameters. The variation in excessive thermodynamic properties as a consequence of possible molecular interactions is discussed.     

Semiclassical variational study of size effects in neutral and charged jellium droplets

An analytic expression for the total energy of metallic clusters composed ofN identical atoms of valencev and with net chargeQ is obtained by means of a variational solution of the Thomas-Fermi-Weizsäcker energy density functional within the spherical jellium model. The minimum energy is given as an expansion in decreasing powers of the cluster radiusR=r _s Z ^1/3, withZ=vN andr _s the radius per electron of the bulk metal. The coefficients are obtained as functions ofr _s . Terms of volume (R ³), surface (R ²), curvature (R), constant (R ⁰), (1/R) and (1/R ²) are clearly separated in the formula, as well as the different contributions (kinetic, coulombic and exchange-correlation) to each of them. The asymptotic values (R→∞) for the work functions,W(r _s ), and surface energies σ(r _s ), are compared to analogous semiclassical and Kohn-Sham calculations of jellium-like surfaces and to the experimental values. The size dependent behaviour of chemical potentials, μ(R), electron affinities,AF(R), and ionization potentials,IP(R), are easily obtained for any kind of metallic clusters. In particular we discuss the Coulomb and quantum corrections to the coefficients β, δ in the asymptotic formulae:IP?W+β/R andAF?W+δ/R.     

Volumetric,viscometric and acoustic properties of binary mixtures of 2-propanol with n -alkanes (C6, C8, C10) at 298.15 and 308.15 K

Densities (ρ), viscosities (η), and speeds of sound, (u) of the binary mixtures of 2-propanol with n-alkanes (n-hexane, n-octane, and n-decane) were measured over the entire composition range at 298.15 and 308.15 K and at atmospheric pressure. Using the experimental values of density, viscosity and speed of sound, the excess molar volumes (V ^E), viscosity deviations (Δη), deviations in speed of sound (Δu), isentropic compressibility (κ _s), deviations in isentropic compressibility (Δκ _s), and excess Gibbs energies of activation of viscous flow (ΔG* ^E) were calculated. These results were fitted to the Redlich–Kister type polynomial equation. The variations of these excess parameters with composition were discussed from the viewpoint of intermolecular interactions in these mixtures. The excess properties are found to be either positive or negative depending on the molecular interactions and the nature of liquid mixtures.     

Theoretical study of Na(4p2P) + Na(3s2S) and Cd(5p3P0) + Na(3s2S) collisions and their role in the energy transfer between Cd.* and Na

We have computed the cross sections for the energy transfer process Cd(5p³P₀) + Na(3s²S) → Cd(5s¹S) + Na(4p²P) and for the state changing collision Na(4p²P) + Na(3s²S) → Na(3d²D) + Na(3s²S), based on theoretical interaction potentials for the NaCd and Na2 systems, respectively. Our calculations shed light on the interpretation of experiments with laser excited Na+Cd vapour mixtures [1]. It turns out that Cd(5p³P₀), in rapid equilibrium with the doorway state Cd(5p³P₁), efficiently transfers energy to Na, populating the 4p²P state. The collisions with ground state Na cause a very fast conversion of the 4p³P₁ to the 3d²D state, from which the strongest emission is observed.     

一个与吸附剂浓度有关的Langmuir等温式

实验测定了不同吸附剂浓度下, 高岭土对Pb(II)和Cu(II)的吸附作用, 结果表明存在明显的吸附剂浓度效应, 即吸附等温线随吸附剂浓度升高而降低. 采用传统的Langmuir 吸附等温式对实验数据进行拟合表明, 此等温式可准确地描述给定吸附剂浓度下的吸附结果, 但不能预测其吸附剂浓度效应. 根据表面组分活度(SCA)模型, 假设吸附剂颗粒间存在相互作用, 吸附剂表面吸附位的活度系数不等于1, 而应为吸附剂浓度的函数, 推导出了一个与吸附剂浓度有关的Langmuir (Langmuir-SCA)方程. 运用高岭土吸附Pb(II)和Cu(II)以及文献中蛭石吸附Zn(II)和Cd(II)、咖啡吸附Pb(II)的实验数据检验方程的适用性, 结果表明Langmuir-SCA方程可准确地描述所观察到的吸附剂浓度效应. 方程的两个内禀参数, 热力学平衡常数(K_eq)和特征饱和吸附量(Γ_m⁰), 与吸附剂浓度无关, 并可由吸附实验数据拟合求得.     

Catalysis of the electrochemical oxygen reduction in room-temperature ionic liquids on a pyrolytic graphite electrode by iron-containing superoxide dismutase

Catalysis of the electrochemical oxygen reduction reaction (ORR) on a pyrolytic graphite electrode (PGE) by iron-containing superoxide dismutase (Fe-SOD) is investigated for the first time using cyclic voltammetry and electrochemical impedance spectroscopy. The study is carried out in three room-temperature ionic liquids (RTILs), namely, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF₄), 1-propyl-3-methylimidazolium tetrafluoroborate (PMIBF₄), and 1-butyl-3-methylimidazolium tetrafluoroborate (EMIBF₄). The results demonstrate that in EMIBF₄, Fe-SOD exhibits the most satisfactory catalysis for ORR, with the standard rate constant of ORR on bare PGE, k _s, increasing from 3.9 to 5.1 times 10⁻³ cm s⁻¹, while in PMIBF₄ and BMIBF₄ containing Fe-SOD k _s increases from 2.6 to 3.6 and from 1.4 to 2.2 times 10⁻³ cm s⁻¹, respectively. In addition to the increased k _s, adding Fe-SOD renders the formal potential of ORR more positive. To accelerate the electron transfer, multi-walled carbon nanotubes (MWCNTs) are employed to modify PGE, consequently, yielding the dramatically increased peak current and k _s. For MWCNTs-modified PGE in EMIBF₄ free of Fe-SOD, k _s increases from 3.9 to ∼7.1 times 10⁻³ cm s⁻¹. The ORR catalysis by Fe-SOD in the presence of Fe-SOD is also evidenced by the formal-potential shift in the positive direction. With MWCNTs accounting for the larger k _s and Fe-SOD being responsible for the formal-potential shift, the catalysis of ORR is satisfactory. Chronocoulmetry experiments proved that some Fe-SOD could be adsorbed on PGE. After analyzing the results, dismutation of superoxide anion O ₂ ⁻ by Fe-SOD is thought to be the main reason for the formal-potential shift. The different polarity of RTILs is probably partly responsible for different k _s obtained in different RTILs. Basing on an earlier proposition, the catalysis of ORR by MWCNTs in RTILs is discussed. Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 9, pp. 1137–1146. The text was submitted by the authors in English.     

UHF-AM1 studies on 1,4 and 1,5 intramolecular H-atom transfer reactions in alkenyl radicals

The transition states of intramolecular 1,4 and 1,5 H-atom transfers, from/to primary (p), secondary (s) or tertiary alkyl (t) and primary (p _a), secondary (s _a) or tertiary (t _a) allyl carbon atoms, have been studied at the level of the semiempirical quantum-chemical method AM1 with the UHF approximation. The activation and reaction enthalpies were calculated and compared with experimental data available in the literature and the calculated data obtained for analogous reactions in alkyl radicals. Correlations were found between the activation enthalpies and the dissociation enthalpies of the bonds broken and formed.     

Collaborative sampling trial in the context of quality assurance in the German marine monitoring programme for the North Sea and the Baltic Sea

This paper presents the assessment of a collaborative trial in sampling in the Baltic Sea in the framework of quality assurance in the German marine monitoring programme for the North Sea and the Baltic Sea. The objective of investigations was to determine the influence of sampling on analytical results for selected monitoring parameters and to harmonize the procedure for sampling of sea water to a large extent. In these studies the staff of three vessels took replicate sea water samples, 1 m below the surface and below the halocline, at two monitoring stations. Mass concentration mean values for different nutrient parameters were obtained from each sample, all in one laboratory. Data produced from the hierarchical design were treated with robust analysis of variance (ANOVA) to generate uncertainty estimates, as standard uncertainties (“u” expressed as standard deviation), for geochemical variation (s _geochem), primary sampling (s _sampling), and chemical analysis (s _analysis). Geochemical variation dominated the total variance in all cases. Sampling and analytical uncertainties contributed together up to 15% of the total variance and had a relative measurement uncertainty (u%) of less than 2% for all the parameters investigated. Thus for this study the sampling protocol and the analytical method could be regarded as fit-for-purpose. M. Gluschke was formerly affiliated to the Federal Environmental Agency, P.O. Box 33 00 22, 14191 Berlin, Germany.     

EPR studies of covalent bonding and hyperfine coupling in the complexes of <Emphasis Type="Italic">ns</Emphasis><Superscript>1</Superscript> ions

Covalent bonding in the complexes containing ns ¹ ions of various metals was studied by EPR spectroscopy. Large series of octahedral, cubic, and cuboctahedral complexes of the ⁶⁷Zn⁺(4s ¹), ¹¹¹Cd⁺(5s ¹), ²⁰⁵Tl²⁺(6s ¹), and ²⁰⁷Pb³⁺(6s ¹) ions were analyzed in crystal structures like fluoroperovskite (KMgF₃), fluoroantiperovskite (LiBaF₃), fluorite (MF₂) (where M = Ca, Sr, and Ba), and alkali metal halides. The parameters of hyperfine couplings and ligand hyperfine couplings were interpreted with regard to bond covalence and spin polarization.     

Trans—cis conformation of N,N′-dimethylthiourea as proved by selected deuteration

Raman spectra of CD₃NHCSNHCH₃ (s-DMTU-d₃) and CD₃NDCSNDCH₃ (s-DMTU-d₅) have shown a doubling of lines near 700 (νCS) and 435 cm⁻¹ (δ NCN/δ NCS). For s-DMTU-d₃ and -d₅ dissolved in light and heavy water, respectively, the doubling has also been observed. On the other hand, the spectra of CH₃NHCSNHCH₃ and CD₃NHCSNHCD₃ (s-DMTU-d₀ and -d₆), as well as their N-deuterated compounds (s-DMTU-d₂ and -d₈), exhibit only a single line in the same spectral region. These findings verify the trans—cis conformation of s-DMTU, since only this conformer can give two different isomers which cause the line doubling.     

Solvent effect on fluorescence spectra of a spirooxazine

Fluorescence and excitation spectra of spironaphthoxazine (SNO) in various solvents have been investigated systematically. The fluorescence in low-polar solvents normally originated from SNO in the excited state. In protic high-polar solvents, fluorescence from an excited intermediate species (X^* _h) relaxed from a part of the excited SNO by breaking a C-O bond in the oxazine ring was also observed. It has been found that a ground-state intermediate species (X_s), transformed from a part of ground-state SNO, is directly excited to its excited state (X_s ^*), which displays fluorescence in aprotic high-polar solvents.     

Preparation,Characterization and Standard enthalpy of formation of Sr2CeO4.

Sr₂CeO₄ has been prepared by sol-combustion and co-precipitate routes and the resulting products have been characterized by XRD analysis. The molar enthalpies of solution of Sr₂CeO₄(s), Sr(NO₃)₂(s) and Ce(NO₃)₃·6H₂O(s) in 0.150 dm^–3 of (4.41 mol dm–3 H₂O₂+4.23 mol dm^–3 of HNO₃) solvent as well as the molar enthalpies of solution of Sr₂CeO₄(s), SrCl₂(s) and CeCl₃(s) in 0.150 dm³ of (1.47 mol dm^–3 H₂O₂+3.05 mol dm^–3 of HClO₄) solvent have been measured using an isoperibol type calorimeter. From these results and other auxiliary data, the standard molar enthalpy of formation of Sr₂CeO₄ has been derived to be –2277.3±3.1 kJ mol^–1 at 298.15 K. This is the first reported thermodynamic data on this compound.     

Production of solvated electrons,ion-paris and alkali metal anions in tetrahydrofuran studied by pulse radiolysis

Pulse radiolysis of tetrahydrofuran (THF) and solutions of NaAIH₄ in THF shows the formation of solvated electrons (e^?_s), their conversion to Na⁺-e^?_s) ion-pairs and ultimately the alkali metal anion (Na^?).     

Acoustical studies of schiff bases in 1,4-dioxane and dimethylformamide at 318.15 K

The density, viscosity, and ultrasonic velocity of solutions of two schiff bases in 1,4-dioxane and dimethylformamide (DMF) were measured at 318.15 K. Various acoustical properties, such as the specific impedance (Z), isentropic compressibility (κ_s), Rao’s molar sound function (R _m), van der Waals constant (b), molar compressibility (W), intermolecular free length (L _f), relaxation strength (r), relative association (R _A), and free volume (V _f), were calculated. The results were interpreted in terms of molecular interactions occurring in the solutions. Published in Russian in Zhurnal Fizicheskoi Khimii, 2006, Vol. 80, No. 7, pp. 1206–1210. The text was submitted by the authors in English.     

A sorbent concentration-dependent Freundlich isotherm

During study of the adsorption isotherms at solid–liquid interfaces, a sorbent concentration effect (C _s-effect) phenomenon was observed. In order to describe the C _s-effect, we proposed a new adsorption model, i.e., surface component activity (SCA) model. It supposes that the interaction between the sorbent particles exists in the real adsorption system, which induces the deviation of a real adsorption system from an ideal one. It is the deviation that induces the emerging of the C _s-effect. Based on the SCA model, the activity coefficient of adsorption sites should be a function of the sorbent concentration (C _s), and a C _s-dependent Freundlich equation (Freundlich-SCA equation) was derived. It was confirmed that the Freundlich-SCA equation can describe the C _s-effect observed in adsorption experiments. Its parameters (n _S and K _S) can be simulated with experimental adsorption data and are independent of C _s. Thus, these parameters obtained at given C _s values can be used to predict the adsorption behavior of the adsorbate at any C _s value.     

Constant-volume combustion energy of the lead salts of 2HDNPPb and 4HDNPPb and their effect on combustion characteristics of RDX–CMDB propellant

The constant-volume combustion energies of the lead salts of 2-hydroxy-3,5-dinitropyridine (2HDNPPb) and 4-hydroxy-3,5-dinitropyridine (4HDNPPb), ΔU _c (2HDNPPb(s) and 4HDNPP(s)), were determined as –4441.92±2.43 and –4515.74±1.92 kJ mol^–1 , respectively, at 298.15 K. Their standard enthalpies of combustion, Δ_c ^m H θ(2HDNPPb(s) and 4HDNPPb(s), 298.15 K), and standard enthalpies of formation, Δ_r ^m H θ(2HDNPPb(s) and 4HDNPPb(s), 298.15 K) were as –4425.81±2.43, –4499.63±1.92 kJ mol^–1 and –870.43±2.76, –796.65±2.32 kJ mol^–1 , respectively. As two combustion catalysts, 2HDNPPb and 4HDNPPb can enhance the burning rate and reduce the pressure exponent of RDX–CMDB propellant.     

The state dependence of the interaction of metastable rare gas atoms Rg*(ms3 P 2,3 P 0) (Rg=Ne,Ar, Kr,Xe) with ground state sodium atoms

Using crossed beams of metastable rare gas atoms Rg*(ms³ P ₂,³ P ₀) (Rg=Ne, Ar, Kr, Xe) and ground state sodium atoms Na(3s ² S _1/2), we have measured the energy spectra of electrons released in the respective Penning ionization processes at thermal collision energies. For Rg*(³ P ₂)+Na(3s), the spectra are quite similar for the different rare gases, both in width and shape; they reflect attractive interactions in the entrance channel with well depthsD* _e [meV] decreasing slowly from Rg=Ne to Xe as follows: 676(18); 602(23); 565(26); 555(30). For Rg*(³ P ₀)+Na(3s), the spectra vary strongly with the rare gas, indicating a change in the character of the interaction from van der Waals type attraction (Ne) to chemical binding for Kr and Xe with well depthsD* _e [meV] of: 51(19); 107(25); 432(30); 530(50). These findings are explained through model calculations of the respective potential curves, in which the exchange and the spin orbit interaction in the excited rare gas and the molecular interaction between the two valences-electrons in terms of suitably chosen singlet and triplet potentials are taken into account. These calculations also explain qualitatively the experimental finding that the ratiosq ₂/q ₀ of the ionization cross sections for Rg*(³ P ₂)+Na and Rg*(³ P ₀)+Na vary strongly with the rare gas from Ne to Xe as follows: 15.8(3.2); 2.6(4); 1.4(2); 1.6(4).