Kinetics and mechanism of thermal polymerization of hexafluoropropylene under high pressures

The basic kinetic parameters of thermal polymerization of hexafluoropropylene, namely, general rate constants, degree of polymerization, and their temperature and pressure dependences in the range of 230–290 °C and 2–12 kbar (200–1200 MPa) were determined. The activation energy (E _act = 132±4 kJ mol⁻¹) and activation volume (ΔV ₀ ^≠ = −27±1 cm³ mol⁻¹) were calculated. The activation energy of thermal initiation of polymerization was estimated. The reaction scheme based on the assumption about a biradical mechanism of polymerization initiation was proposed.     

Accurate calculations of dissociation energies of weakly bonded He<Subscript>2</Subscript> and Be<Subscript>2</Subscript> molecules by MRCI method

The He₂ and Be₂ ground state potential curves have been calculated by extrapolating to an infinite basis BSSE corrected MRCI total energies obtained with large Gaussian basis sets, large reference configuration spaces, and pseudo-natural molecular orbitals. The calculated D _e = 11.0031 K and R _e = 5.607 a.u. of He₂ are in an excellent agreement with D _e = 11.006 ± 0.004 K and R _e = 5.608 ± 0.012 a.u. obtained recently by SAPT with SM energy correction. The obtained Be₂ non-relativistic D _e = 822 cm⁻¹ and relativistically corrected D _e = 818 cm⁻¹ are in a good agreement with experimental D _e = 790 ± 30 cm⁻¹ and the value of 829 ± 64 cm⁻¹ obtained recently by a quantum Monte Carlo method.     

Pseudopotential study of lanthanum and lutetium dimers

Relativistic energy-consistent small-core lanthanide pseudopotentials of the Stuttgart–Bonn variety and extended valence basis sets have been used for the investigation of the dimers La₂ and Lu₂. It was found that the ground states for La₂ and Lu₂ are most likely ¹∑ _g ⁺ (σ _g ²π _u ⁴) and ³∑ _g ⁻ (4f ¹⁴4f ¹⁴σ _g ²σ _u ²π_u ²), respectively. The molecular constants including error bars were derived from multireference configuration interaction as well as coupled-cluster calculations, taking into account corrections for atomic spin–orbit splitting as well as possible basis set superposition errors. The theoretical values for La₂ (R _e=2.70±0.03 ?, D _e=2.31±0.13 eV, ω_e=186±13 cm⁻¹) show good agreement with the experimental binding energy (D _e=2.52±0.22 eV), but the experimental vibrational constant in an Ar matrix (ω_e=236±0.8 cm⁻¹) is significantly higher. For Lu₂ the theoretical values (R _e=3.07±0.03 ?, D _e=1.40±0.12 eV, ω_e=123±1 cm⁻¹) are in overall excellent agreement with experimental data (D _e=1.43±0.34 eV, ω_e=122± 1 cm⁻¹). The electronic structures of La₂ and Lu₂ are compared to those other lanthanide dimers and trends in the series are discussed. Received: 25 March 2002 / Accepted: 2 June 2002 / Published online: 21 August 2002     

Spectroscopic study of protonation of oligonucleotides containing adenine and cytosine

Acidobasic properties of purine and pyrimidine bases (adenine, cytosine) and relevant nucleosides (adenosine, cytidine) were studied by means of glass-electrode potentiometry and the respective dissociation constants were determined under given experimental conditions (I = 0.1 M (NaCl), t = (25.0 ± 0.1) °C): adenine (pK _HL = 9.65 ± 0.04, pK _H2L = 4.18 ± 0.04), adenosine (pK _H2L = 3.59 ± 0.05), cytosine (pK _H2L = 4.56 ± 0.01), cytidine (pK _H2L = 4.16 ± 0.02). In addition, thermodynamic parameters for bases: adenine (ΔH ⁰ = (−17 ± 4) kJ mol⁻¹, ΔS ⁰ = (23 ± 13) J K⁻¹ mol⁻¹), cytosine (ΔH ⁰ = (−22 ± 1) kJ mol⁻¹, ΔS ⁰ = (13 ± 5) J K⁻¹ mol⁻¹) were calculated. Acidobasic behavior of oligonucleotides (5′CAC-CAC-CAC3′ = (CAC)₃, 5′AAA-CCC-CCC3′ = A₃C₆, 5′CCC-AAA-CCC3′ = C₃A₃C₃) was studied under the same experimental conditions by molecular absorption spectroscopy. pH-dependent spectral datasets were analyzed by means of advanced chemometric techniques (EFA, MCR-ALS) and the presence of hemiprotonated species concerning (C⁺-C) a non-canonical pair (i-motif) in titled oligonucleotides was proposed in order to explain experimental data obtained according to literature.     

Potentiometric and Multinuclear Magnetic Resonance Study of the Solution Equilibria Between Aluminium(III) Ion and L-Aspartic Acid

Solution equilibria between aluminium(III) ion and L-aspartic acid were studied by potentiometric, ²⁷Al, ¹³C, and ¹H NMR measurements. Glass electrode equilibrium potentiometric studies were performed on solutions with ligand to metal concentration ratios 1:1, 3:1, and 5:1 with the total metal concentration ranging from 0.5 to 5.0 mmol/dm³ in 0.1 mol/dm³ LiCl ionic medium, at 298 K. The pH of the solutions was varied from ca. 2.0 to 5.0. The non-linear least squares treatment of the data performed with the aid of the Hyperquad program, indicated the formation of the following complexes with the respective stability constants log β_p,q,r given in parenthesis (p, q, r are stoichiometric indices for metal, ligand, and proton, respectively): Al(HAsp)²⁺ (log β_1,1,1 = 11.90 ± 0.02); Al(Asp)⁺ (log β_1,1,0 = 7.90 ± 0.03); Al(OH)Asp⁰ (log β_1,1,−1 = 3.32 ± 0.04); Al(OH)₂Asp⁻ (log β_1,1−2 = −1.74 ± 0.08), and Al₂(OH) Asp³⁺ (log β_2,1,−1 = 6.30 ± 0.04). ²⁷Al NMR spectra of Al³⁺ + aspartic acid solutions (pH 3.85) indicate that sharp symmetric resonance at δ∼10 ppm can be assigned to (1, 1, 0) complex. This resonance increases in intensity and slightly broadens upon further increasing the pH. In Al(Asp)⁺ complex the aspartate is bound tridentately to aluminum. The ¹H and ¹³C NMR spectra of aluminium + aspartic acid solutions at pH 2.5 and 3.0 indicate that β-methylene group undergoes the most pronounced changes upon coordination of aluminum as well as α-carboxylate group in ¹³C NMR spectrum. Thus, in Al(HAsp)²⁺ which is the main complex in this pH interval the aspartic acid acts as a bidentate ligand with –COO⁻ and –NH₂ donors closing a five-membered ring.     

Potentiometric and Multinuclear Magnetic Resonance Study of the Solution Equilibria Between Aluminium(III) Ion and L-Aspartic Acid

Summary. Solution equilibria between aluminium(III) ion and L-aspartic acid were studied by potentiometric, ²⁷Al, ¹³C, and ¹H NMR measurements. Glass electrode equilibrium potentiometric studies were performed on solutions with ligand to metal concentration ratios 1:1, 3:1, and 5:1 with the total metal concentration ranging from 0.5 to 5.0 mmol/dm³ in 0.1 mol/dm³ LiCl ionic medium, at 298 K. The pH of the solutions was varied from ca. 2.0 to 5.0. The non-linear least squares treatment of the data performed with the aid of the Hyperquad program, indicated the formation of the following complexes with the respective stability constants log β_p,q,r given in parenthesis (p, q, r are stoichiometric indices for metal, ligand, and proton, respectively): Al(HAsp)²⁺ (log β_1,1,1 = 11.90 ± 0.02); Al(Asp)⁺ (log β_1,1,0 = 7.90 ± 0.03); Al(OH)Asp⁰ (log β_1,1,−1 = 3.32 ± 0.04); Al(OH)₂Asp⁻ (log β_1,1−2 = −1.74 ± 0.08), and Al₂(OH) Asp³⁺ (log β_2,1,−1 = 6.30 ± 0.04). ²⁷Al NMR spectra of Al³⁺ + aspartic acid solutions (pH 3.85) indicate that sharp symmetric resonance at δ∼10 ppm can be assigned to (1, 1, 0) complex. This resonance increases in intensity and slightly broadens upon further increasing the pH. In Al(Asp)⁺ complex the aspartate is bound tridentately to aluminum. The ¹H and ¹³C NMR spectra of aluminium + aspartic acid solutions at pH 2.5 and 3.0 indicate that β-methylene group undergoes the most pronounced changes upon coordination of aluminum as well as α-carboxylate group in ¹³C NMR spectrum. Thus, in Al(HAsp)²⁺ which is the main complex in this pH interval the aspartic acid acts as a bidentate ligand with –COO⁻ and –NH₂ donors closing a five-membered ring.     

Ion-pair formation in the outer-sphere electron transfer reactions between tris-(1, 10) phenanthroline iron(II) and the halopentacyanocobaltate(III) complexes in aqueous acidic solutions

The kinetics of the reactions between Fe(phen) ₃ ²⁺ [phen = tris–(1,10) phenanthroline] and Co(CN)₅X³⁻ (X = Cl, Br or I) have been investigated in aqueous acidic solutions at I = 0.1 mol dm⁻³ (NaCl/HCl). The reactions were carried out at a fixed acid concentration ([H⁺] = 0.01 mol dm⁻³) and the second-order rate constants for the reactions at 25 °C were within the range of (0.151–1.117) dm³ mol⁻¹ s⁻¹. Ion-pair constants K _ip for these reactions, taking into consideration the protonation of the cobalt complexes, were 5.19 × 10⁴, 3.00 × 10² and 4.02 × 10⁴ mol⁻¹ dm⁻³ for X = Cl, Br and I, respectively. Activation parameters measured for these systems were as follows: ΔH* (kJ K⁻¹ mol⁻¹) = 94.3 ± 0.6, 97.3 ± 1.0 and 109.1 ± 0.4; ΔS* (J K⁻¹) = 69.1 ± 1.9, 74.9 ± 3.2 and 112.3 ± 1.3; ΔG* (kJ) = 73.7 ± 0.6, 75.0 ± 1.0 and 75.7 ± 0.4; E _a (kJ) = 96.9 ± 0.3, 99.8 ± 0.4, and 122.9 ± 0.3; A (dm³ mol⁻¹ s⁻¹) = (7.079 ± 0.035) × 10¹⁶, (1.413 ± 0.011) × 10¹⁷, and (9.772 ± 0.027) × 10²⁰ for X = Cl, Br, and I respectively. An outer – sphere mechanism is proposed for all the reactions.     

The Molecular Structure and the Puckering Potential Function of Octamethylcyclotetrasilane,Si4Me8, Determined by Gas Electron Diffraction and Relaxation Constraints from Ab Initio Calculations

Gas electron diffraction data are applied to determine the geometrical parameters of the octamethylcyclotetrasilane molecule using a dynamic model in which the ring puckering is treated as a large amplitude motion. The structural parameters and parameters of the potential function were refined, taking into account the relaxation of the molecular geometry estimated from ab initio calculations at the Hartree–Fock level of theory using a 6-311G** basis set. The potential function has been described as V() = V ₀[(/ _e )² – 1]² with V ₀ = 1.0 ± 0.5 kcal/mol and _e = 28.3 ± 1.9°, where is the puckering angle of the ring. The geometric parameters at the minimum of V() (r _a in Å, in degrees and errors given as three times the standard deviations including a scale error) are as follows: r(Si—C)_av = 1.894(3), r(Si—Si) = 2.363(3), r(C—H) = 1.104(3), CSiC = 109.5(6), SiSiSi = 88.2(2), SiCH = 111.7(6), C = 4.1, where the tilt C was estimated from ab initio constraints. The structural parameters are compared with those obtained for related compounds.     

The structure and thermochemistry of 3:4,5:6-dibenzo-2-hydroxymethylene-cyclohepta-3,5-dienenone (1) and some related compounds

Condensed and gas phase enthalpies of formation of 3:4,5:6-dibenzo-2-hydroxymethylene-cyclohepta-3,5-dienenone (1, (−199.1 ± 16.4), (−70.5 ± 20.5) kJ mol⁻¹, respectively) and 3,4,6,7-dibenzobicyclo[3.2.1]nona-3,6-dien-2-one (2, (−79.7 ± 22.9), (20.1 ± 23.1) kJ mol⁻¹) are reported. Sublimation enthalpies at T=298.15 K for these compounds were evaluated by combining the fusion enthalpies at T = 298.15 K (1, (12.5 ± 1.8); 2, (5.3 ± 1.7) kJ mol⁻¹) adjusted from DSC measurements at the melting temperature (1, (T _fus, 357.7 K, 16.9 ± 1.3 kJ mol⁻¹)); 2, (T _fus, 383.3 K, 10.9 ± 0.1) kJ mol⁻¹) with the vaporization enthalpies at T = 298.15 K (1, (116.1 ± 12.1); 2, (94.5 ± 2.2) kJ mol⁻¹) measured by correlation-gas chromatography. The vaporization enthalpies of benzoin ((98.5 ± 12.5) kJ mol⁻¹) and 7-heptadecanone ((94.5 ± 1.8) kJ mol⁻¹) at T = 298.15 K and the fusion enthalpy of phenyl salicylate (T _fus, 312.7 K, 18.4 ± 0.5) kJ mol⁻¹) were also determined for the correlations. The crystal structure of 1 was determined by X-ray crystallography. Compound 1 exists entirely in the enol form and resembles the crystal structure found for benzoylacetone.     

Molecular Structure and Internal Rotation Potential of Dimethylphenylphosphine, According to Gas-Phase Electron Diffraction Data and Quantum-Chemical Calculations

Geometric parameters of dimethylphenylphosphine molecule were determined by gas-phase electron diffraction using a dynamic model in which the rotation of the PMe₂ group is treated as large-amplitude motion. Refinement of the structural parameters and parameters of the potential function was performed taking into account the geometry relaxation on the basis of HF/6-311++G** calculations. The internal rotation potential has a single minimum at 0° ( is the angle between the bisector of the MePMe angle and the phenyl ring plane) and may be described by the function of the form V() = 0.5V ₂(1 - cos2), where V ₂ = 0.38±0.36 kcal mol^{- 1}. The data obtained are compared with those for related molecules. Steric effects affect the geometry of the phenylphosphine molecule more significantly than does p- interaction.     

Density functional theory study on organic semiconductor for field effect transistors: Symmetrical and unsymmetrical porphyrazine derivatives with annulated 1,2,5-thiadiazole and 1,4-diamyloxybenzene moieties

Density functional theory (DFT) calculations were carried out to investigate the organic field effect transistor (OFET) performance of the symmetrical metal-free tetrakis (1,2,5-thiadiazole) porphyrazine (S₄)PzH₂ and tetrakis (1,4-diamyloxybenzene) (A₄)PzH₂ as well as the low-symmetry metal-free porphyrazine with annulated 1,2,5-thiadiazole and 1,4-diamyloxybenzene groups in the ratio 2:2 (cis) and 1:3, that is, (cis-S₂A₂)PzH2 and (SA₃)PzH₂, (S = 1,2,5-thiadiazole ring, A = annulated 1,4-diamyloxy-benzene ring, Pz = porphyrazine) in terms of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy, ionization energy (IE), electron affinity (EA), and their reorganization energy (λ) during the charge-transport process. On the basis of Marcus electron transfer theory, electronic couplings (V) and field effect transistor (FET) properties for the four compounds with known crystal structure have been calculated. The electron transfer mobility (μ₋) is revealed to be 0.056 cm²·V⁻¹·s⁻¹ for (S₄)PzH₂. The hole transfer mobility (μ₊) is 0.075, 0.098, and 8.20 cm²·V⁻¹·s⁻¹ for (cis-S₂A₂)PzH₂, (SA₃)PzH₂, and (A₄)PzH₂, respectively. The present work represents the theoretical effort towards understanding the OFET properties of symmetrical and unsymmetrical porphyrazine derivatives with annulated 1,2,5-thiadiazole and 1,4-diamyloxybenzene. Supported by the National Natural Science Foundation of China (Grant No. 50673051) and Beijing Municipal Commission of Edueation     

Interaction dipole moment in Rg–Xe (Rg = He, Ne, Ar, and Kr) heterodiatoms from conventional ab initio and density functional theory calculations

We have obtained interaction dipole moment curves for the rare gas heterodiatoms Rg...Xe (Rg = He, Ne, Ar, and Kr) from conventional ab initio and density functional theory calculations with flexible Gaussian-type basis sets. All methods seem to reproduce fairly similar dipole moment curves for all pairs. Our best values for the interaction dipole moment (at the respective experimental equilibrium separation R _e) were obtained at the coupled-cluster theory with single, double, and perturbatively linked triple excitations level of theory: μ_int(RgXe)/eα₀ = − 0.0025(He), − 0.0047(Ne), − 0.0055(Ar), and − 0.0037(Kr). The same trend (in absolute terms) is observed at the MP2 level of theory for the derivative of the dipole moment at R _e, as (dμ_int (RgXe)/dR) _e /e = 0.0043 (He), 0.0082 (Ne), 0.0091 (Ar), and 0.0059 (Kr). Around R _e , μ_int(HeXe) ≡ μ_HeXe varies at the MP2 level of theory as [μ_HeXe(R) − μ_HeXe(R _e)]/ea₀ = 0.0043(R − R _e) − 0.0033(R − R _e)² + 0.0018(R − R _e)³ − 0.0005(R − R _e)⁴.     

Electron transfer. 138. Potentials involving chelated chromium(V)

The bis(chelated) complex of Cr^V(0) derived from the dianion (L^{2 −}) of 2-ethyl-2-hydroxybutanoic acid is readily reduced to a bis(chelate of Cr^III, featuring the monoanion (LH⁻) [Cr ^V(0)(L²⁻)₂]⁻+4H⁺+H₂O+2e⁻→[Cr^III(OH₂)₂(LH⁻ ₂]⁺ of this acid. Potentials estimated by Ghosh in 1993 for this 2e⁻ change, E⁰ (pH 0) 1.32 V, E^eff (pH 3.3) 0.93 V, are in accord with the nearly irreversible reductions of the Cr(V) species (in 1∶1 ligand buffer) by Fe²⁺, V0²⁺, IrCl₆ ^{3 −} and I⁻, whereas lower values reported by Bose in 1996, E⁰ (pH 0) 0.84 V, E^eff (pH 3.3) 0.45 V, are potentiometrically inconsistent with these conversions. A similar discrepancy is noted for potentials for Cr(V,IV) estimated in 1996, E⁰ (pH 0) 0.84 V, E^eff (pH 3.3) 0.46 V, which, wholly contrary to observation, predict that the reductions of excess Cr(V) to CR(IV) by Fe²⁺, V0²⁺, and I⁻ are thermodynamically disfavored.     

Complexation of [2.2]paracyclophane with β- and γ-cyclodextrins studied by HPLC and NMR

The NMR spectra of [2.2]paracyclophane with β- or γ-cyclodextrin in DMF-d₇ at room temperature do not show significant complexation, while HPLC of the complexes in mixed H₂O:alcohol solvents demonstrate complexation with different stoichiometries. At 243 K in DMF solution the H3 and H5 NMR signals of γ-cyclodextrin (but not β) exhibit complexation-induced chemical shifts denoting complex formation. According to HPLC, at room temperature the [2.2]paracyclophane complex with β-cyclodextrin in 20% H₂O:EtOH exhibits 1:2 stoichiometry with K ₁ = 1×10² ± 2, K ₂ = 9.0×10⁴ ± 2×10³ (K = 9×10⁶) while that with γ-cyclodextrin in 50% H₂O:MeOH exhibits 1:1 stoichiometry with K ₁ = 4×10³ ± 150 M⁻¹. Thermodynamic parameters for both complexes have been estimated from the retention time temperature dependence. For the β-cyclodextrin complexation at 25°C ΔG ⁰ _CD is −39.7 kJ mol⁻¹ while ΔH ⁰ _CD and ΔS ⁰ _CD are −88.2 kJ mol⁻¹ and −0.16 kJ mol⁻¹ K⁻¹. For γ-cyclodextrin, the corresponding values are ΔG ⁰ _CD = −20.5 kJ mol⁻¹, ΔH ⁰ _CD = −33.5 kJ mol⁻¹ and ΔS ⁰ _CD = −0.04 kJ mol⁻¹ K⁻¹.      

Oxygen reduction in acid media by a Ru<Subscript>x</Subscript>Fe<Subscript>y</Subscript>Se<Subscript>z</Subscript>(CO)<Subscript>n</Subscript> cluster catalyst dispersed on a glassy carbon-supported Nafion film

Electrocatalytic oxygen reduction was studied on a Ru_xFe_ySe_z(CO)_n cluster catalyst with Vulcan carbon powder dispersed into a Nafion film coated on a glassy carbon electrode. The synthesis of the electrocatalyst as a mixture of crystallites and amorphous nanoparticles was carried out by refluxing the transition metal carbonyl compounds in an organic solvent. Electrocatalysis by the cluster compound is discussed, based on the results of rotating disc electrode measurements in a 0.5 M H₂SO₄. A Tafel slope of −80.00±4.72 mV dec⁻¹ and an exchange current density of 1.1±0.17×10⁻⁶ mA cm⁻² was calculated from the mass transfer-corrected curve. It was found that the electrochemical reduction reaction follows the kinetics of a multielectronic (n=4e⁻) charge transfer process producing water, i.e. O₂+4H⁺+4e⁻→2H₂O. Electronic Publication     

Composition and formation kinetics of strontium polyvanadates in vanadium(IV,V) solutions

The phase and chemical compositions of the precipitates forming in the Sr(VO₃)₂-VOCl₂-H₂O system in the V⁴⁺/V⁵⁺ = 0.11–9 range at 80–90°C are reported. At pH 1–3 and V⁴⁺/V⁵⁺ = 0.25−9, the general formula of the precipitated compounds is Sr _x V _y ⁴⁺ V_12−y ⁵⁺O_31−δ·nH₂)(0.37 ≤ x ≤ 1.0, 1.7 ≤ y ≤ 3.0, 0.95 ≤ δ ≤ 2.1). Polyvanadates containing the largest amount of vanadium(IV) are obtained at an initial V⁴⁺/V⁵⁺ ratio of 9 and pH 1.9. Precipitation from solutions at pH 3 takes place only in the presence of the VO²⁺ ion, and the highest precipitation rate is observed at V⁴⁺/V⁵⁺ = 0.11. The process is controlled by a second-order reaction on the polyvanadate surface. Under hydrothermal conditions at 180°C, Sr_0.25V₂O₅·1.5H₂O nanorods are obtained from solutions with a V⁴⁺/V⁵⁺ molar ratio of 0.1 at pH 3. The nanorods, 30–100 nm in diameter and up to 2–3 μm in length, have a layered structure with an interlayer spacing of 10.53 ± 0.08 ?.     

Solid-solute phase equilibria in aqueous solution. VI. Solubilities,complex formation,and ion-interaction parameters for the system Na+−Mg2+−ClO 4 − −CO2−H2O at 25°C

The stoichiometric solubility constant of eitelite (NaMg _0.5 CO ₃ +2H⁺ ⇄ Na⁺+0.5Mg ²⁺ +CO ₂ (g)+H ₂ O, log^*K _pso ^I =14.67±0.03 was determined at I=3 m (mol kg⁻¹) (NaClO ₄ ) and 25°C. The stability of magnesium (hydrogen-)carbonato complexes in this ionic medium was explicitely taken into account. Consequently, trace activity coefficients of free ionic species, calculated from the Pitzer model with ion-interaction parameters from the literature, were sufficient for an evaluation of the thermodynamic solubility constants and Gibbs energies of formation for eitelite (−1039.88±0.60), magnesite (−1033.60±0.40), hydromagnesite (−1174.30±0.50), nesquehonite (−1724.67±0.40), and brucite (−835.90±0.80 kJ-mol ⁻¹ ). The increasing solubilities of nesquehonite and eitelite at higher sodium carbonate molalities were explained by invoking a magnesium dicarbonato complex (Mg²⁺+2CO ₃ ²⁻ ⇄ Mg(CO₃) ₂ ²⁻ , log β_z = 3.90 ± 0.08). A set of ion-interaction parameters was obtained from solubility and dissociation constants for carbonic acid in 1 to 3.5 m NaClO ₄ media which reproduce these constants to 0.02 units in log K. The following Pitzer parameters are consistent with the previously studied formation of magnesium (hydrogen-)carbonato complexes in 3m NaClO ₄ . The model and Gibbs functions of solid phases derived here reproduce original solubility data (−log [H⁺], [Mg ²⁺ ] _tot ) measured in perchlorate medium within experimental uncertainty. Presented at the XXII International Conference on Solution Chemistry, July 14–19, 1991, Linz, Austria.     

Studies on the electrochemical and thermodynamic behaviour of Hg-HgS electrode in the presence of sulphide ions

Mercury-mercury (II) sulphide electrode has been prepared and its electrochemical and thermodynamic behaviour has been studied in different media. The electrode is found to show Nernstian response to pS (− log [S²⁻]) over the range 5.19–10.38. In the pH range 7.96–11.98, at constant [S²⁻]_v, its response is also Nernstian. The values of thermodynamic functions, viz., ΔG⁰. ΔH⁰, and ΔS⁰ for the electrode reaction: Hg₍₃)+S²⁻ _aμ ⇌HgS_(s)+2e, have been determined. Further, the standard free energy of formation (ΔG _f ⁰ ) and solubility product constant (K _vp ) of HgS in aqueous medium at 25±0.1°C have also been determined.     

Chemiluminescence activated by Β- diketonate complexes of Eu3+ in the thermolysis of diphenyldiazomethane in the presence of oxygen

Chemiluminescence activated by the chelates Eu(tta)₃phen and Eu(dbm)₃phen in the thermal decomposition of diphenyldiazomethane in benzene in the presence of oxygen was examined at 333 K. The following photophysical characteristics of the luminescence emitter, excited triplet benzophenone (BP), were found: the phosphorescence quantum yield ϕ _BP ⁰ = 1.0 × 10⁻⁵, the true lifetime τ _BP ⁰ = 7 × 10⁻⁸ s, and the rate constant of radiative deactivationk _{r, BP} = ϕ _BP ⁰ τ _BP ^{0 −1} = 160 s⁻¹.