EPR and IR studies on the local structure of 80MoO3–20B2O3 glass

EPR lineshape simulation studies have been performed on a specimen of 80MoO₃–20B₂O₃ glass in the temperature range of 300–77 K. The values of the obtained spin Hamiltonian parameters are: g=1.940, g=1.974, A=150.0×10⁻⁴ cm⁻¹, A=35.6×10⁻⁴ cm⁻¹ and g=1.935, g=1.975, A=141.9×10⁻⁴ cm⁻¹, A=34.5×10⁻⁴ cm⁻¹ at 300 and 77 K, respectively. The paramagnetic site in the specimen is molybdenyl, MoO³⁺, ion in which the Mo is in a distorted octahedral environment of six oxygen atoms with C_4v symmetry. The 11-parallel and 11-perpendicular line feature of the EPR lineshape shows that two Mo nuclei are magnetically equivalent in the glassy matrix, in the temperature range 300–77 K.     

The infrared spectrum of gaseous Sb4O6

The vibrational spectrum of Sb₄O₆ in the gas phase has been measured at 1000 K by high-temperature infrared spectroscopy. The four infrared-active absorption bands were observed at ν₇ = 785.0 cm¹, ν₈ = 176.2 cm⁻¹, ν₉ = 292.4 cm⁻¹ and ν₁₀ = 415.6 cm⁻¹. By combining these results with data on the molecular geometry and the infrared-inactive modes, as reported in the literature, the thermodynamic functions of Sb₄O₆ have been calculated.     

Time-resolved vibrational cemiluminescence: Rate constants for the reaction F + HC1 → HF + Cl and for the relaxtion of HF(v = 3) by HCl, CO2, N2O, CO, N2 and O2

The reaction: F + HCl→ HF (v 3) + Cl (1), has been initiated by photolysing F₂ using the fourth-harmonic output at 266 nm from a repetitively pulsed Nd: YAG laser By analysing the time-dependence of the HF(3,0) vibrational chemiluminescence, rate constants have been determined at (296 ± 5) K for reaction (1), k₁ = (7.0 ± 0.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, and for the relaxation of HF(v = 3) by HCl, CO₂, N₂O, CO, N₂ and O₂: k_HCl = (1.18 ±0.14) × 10⁻¹¹ k_CO2 = (1.04 ± 0. 13) × 10⁻¹², k_N2O = (1.41 ± 0.13) × 10⁻¹¹ k_CO = (2.9 ± 0.3) × (10⁻¹², k_N2 = (7.1 ± 0.6) × 10⁻¹⁴ and k_O2 = (1.9 ± 0.6) × 10⁻¹⁴ cm³molecule⁻¹s⁻¹.     

Crystal structure and some properties of a novel potent Cu2Zn2SOD model schiff base copper(II) complex ∗[Cu(bppn)](ClO4)2∗2 · H2O

The compound *[Cu(bppn)](ClO₄)₂*₂ · H₂O (where BPPN = N,N′-propylenebis[2-benzoylpyridineiminato]) was prepared by reaction of 2-benzoylpyridine and 1,3-propanediamine with copper perchorate in ethanol and characterised by X-ray crystallography. The central Cu atom in two crystallographical non-equivalent [Cu(bppn)]²⁺ cations exhibited a slightly distorted tetrahedral geometry with the Cu---N bond distances of 1.967(5)–2.010(5) Å and 1.966(5)–2.000(5) Å, respectively. The electronic absorption ₆₄₆ was 194 M⁻¹ cm⁻¹. The EPR parameters g = 2.051 and g = 2.226 were in accordance with the respective values of intact Cu₂Zn₂ superoxide dismutase (Cu₂Zn₂SOD). Its electronic property displayed a single quasiversible one—electron reduction process at − 0.204 V with ΔE_p = 84 mV, suggesting the title complex possesses high superoxide dismutase (SOD) activity.     

Comparison of the effects of visible femtosecond laser pulses and continuous wave laser radiation of low average intensity on the clonogenicity of Escherichia coli.

To evaluate the contribution of local pulsed heating of light-absorbing microregions to biochemical activity, irradiation of Escherichia coli was carried out using femtosecond laser pulses (λ = 620 nm, τ_p=3 × 10⁻¹³ s, f_p = 0.5 Hz, E_p = 1.1 × 10⁻³J cm⁻², I_av = 5.5 × 10⁻⁴ W cm⁻², I_p = 10⁹ W cm⁻²) and continuous wave (CW) laser radiation (λ = 632.8 nm, I = 1.3 W cm⁻²). The irradiation dose required to produce a similar biological effect (a 160%–190% increase in the clonogenic activity of the irradiated cells compared with the non-irradiated controls) is a factor of about 10³ lower for pulsed radiation than for CW radiation (3.3 × 10⁻¹ and 7.8 × 10² J cm⁻² respectively). The minimum size of the microregions transiently heated on irradiation with femtosecond laser pulses is estimated to be about 10 Å, which corresponds to the size of the chromophores of hypothetical primary photoacceptors—respiratory chain components.     

Acidity constants of benzidine in aqueous solutions

The acidity constants of benzidine (Bz) in aqueous solutions determined potentiometrically at 25° were K_a1 = (1.11 ± 0.08) × 10⁻⁵, K_a2 = (1.45 ± 0.12) × 10⁻⁴. The apparent mixed constants in 0.1M sodium nitrate are K_a1 = (5.37 ± 0.28) × 10⁻⁶ and K_a2 = (1.14 ± 0.09) × 10⁻⁴. The ultraviolet spectra were recorded as a function of pH and analysed with these constants to obtain the absorption spectra of H₂Bz²⁺, HBz⁺ and Bz; the corresponding wavelengths of maximal absorption are 247, 273 and 278 nm, and molar absorptivities 1.63 × 10⁴, 1.76 × 10⁴ and 2.26 × 10⁴ 1.mole⁻¹.cm⁻¹.     

Rate constants for the reaction of OH radicals with CH3CN, C2H5CN AND CH2=CH-CN in the temperature range 298–424 K

Rate constants for the reactions of OH with CH₃CN, CH₃CH₂CN and CH₂=CH-CN have been measured to be 5.86 × 10⁻¹³ exp(−1500 ± 250 cal mole⁻¹/RT), 2.69 × 10⁻¹³ exp(−1590 ± 350 cal mole⁻¹/RT and 4.04 × 10⁻¹² cm³ molecule⁻¹ s⁻¹, respectively in the temperature range 298–424 K. These results are discussed in terms of the atmospheric lifetimes of nitrfles.     

Novel CO2 selectively permeating membranes containing PETEDA dendrimer

Pentaerythrityl tetraethylenediamine (PETEDA) dendrimer was synthesized from pentaerythrityl tetrabromide and ethylenediamine. Its molecular structure was characterized by elemental analysis, Fourier transform infrared resonance (FT-IR) and hydrogen nuclear magnetic resonance (¹H NMR) spectroscopy. The composite membranes for selectively permeating CO₂ were prepared by using PETEDA-PVA blend polymer as the active layer and polyethersulfone (PES) ultrafiltration membrane as the support layer and their permselectivity was tested by pure CO₂ and CH₄ gases and the gas mixture containing 10 vol.% CO₂ and 90 vol.% CH₄, respectively. For pure gases, the membrane containing 78.6 wt% PETEDA and 21.4 wt% PVA in the blend has a CO₂ permeance of 8.14 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ and CO₂/CH₄ selectivity of 52 at 143.5 cmHg feed gas pressure. While feed gas pressure is 991.2 cmHg, CO₂ permeance reaches 3.56 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ and CO₂/CH₄ selectivity is 19. For the gas mixture, the membrane has a CO₂ permeance of 6.94 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ with a CO₂/CH₄ selectivity of 33 at 188.5 cmHg feed gas pressure, and a CO₂ permeance of 3.29 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ with a CO₂/CH₄ selectivity of 7.5 at a higher feed gas pressure of 1164 cmHg. A possible gas transport mechanism in the composite membranes is proposed by investigating the permeating behavior of pure gases and the gas mixture and analyzing possible reactions between CO₂/CH₄ gases and the PETEDA-PVA blend polymer. The effect of PETEDA content in the blend polymer on permselectivity of the composite membranes was investigated, presenting that CO₂ permeance and CO₂/CH₄ selectivity increase and CH₄ permeance decreases, respectively with PETEDA content. This is explained by that with increasing PETEDA content, the carrier content increases, and the crystallinity and free volume of the PETEDA-PVA blend decrease that were confirmed by the experimental results of X-ray diffraction spectra (XRD) and positron annihilation lifetime spectroscopy (PALS).     

Mechanical stability and transport properties of the Sn-promoted SrCo0.8Fe0.2O3−δ ceramic membrane

In this article, the phase compositions, thermal, mechanical and transport properties of both the SrCo_0.8Fe_0.2O_3−δ (SCF) and the SrCo_0.8Fe_0.1Sn_0.1O_3−δ (SSCF) ceramic membranes were investigated systematically. As compared with the SCF membrane, the SSCF one had a more promoted thermal shock resistance, which related to its small thermal expansion coefficient between them and an enhanced composite structure for it. For the SCF membrane, a permeation rate of 1.9 × 10⁻⁶ mol cm⁻² s⁻¹ was obtained at 1000 °C and under the oxygen partial pressure gradient of P_O2 (h)/P_O2 (l) = 0.209 atm/0.012 atm; however, the permeation rate was 2.5 × 10⁻⁶ mol cm⁻² s⁻¹ for the SSCF one in the same measuring condition. In addition, both peak values of total electrical conductivity (σ_e) for SSCF sample appeared with increasing temperature. The second peak value of σ_e for SSCF one was regarded as the contribution from its minor phase, which appeared with the mixed conducting behavior resulting from partly Co-dissolving into its lattice.     

A monomeric bacteriochlorophyll triplet state (B) in reaction centres of Rhodobacter sphaeroides R26, studied by absorption-detected magnetic resonance

Using absorption-detected magnetic resonance, a new triplet state was observed in reaction centres of Rhodobacter sphaeroides R26 at 7 K. Its zero-field splitting parameters &|;D&|; = 220.5 × 10⁻⁴ cm⁻¹ and &;|;E&|; = 65.4 × 10⁻⁴ cm⁻¹, its spin polarization and its microwave-induced absorption spectrum indicate that it belongs to one of the accessory monomeric bacteriochlorophyll molecules and that it is populated through the same excitation path as the primary donor triplet ³P₈₇₀, via the radical pair ³[P₈₇₀⁺H⁻].     

Thermal stability of osmium mixed oxides I. CaOsO3 decomposition products: A new orthorhombic phase Ca2Os2O7

The thermal decomposition of CaOsO₃ by differential thermal analyses, thermogravimetry and X-ray powder diffraction has been studied. In nitrogen CaOsO₃ decomposes at 880 ± 10°C into CaO, osmium metal and oxygen due to the reaction CaOsO₃ → CaO + Os + O₂. In static air the decomposition occurs in three stages: 2CaOsO₃ + 1/2O₂ → Ca₂Os₂O₇ (in region 775–808°C), Ca₂Os₂O₇ → Ca₂Os₂O_6,5 + 1/4O₂ (at a temperature interval of 850–1000°C) and in the third stage Ca₂Os₂O_6,5 → 2CaO + OsO₄ ÷ 1/4 O₂ (at 1005 ± 5°C). The first intermediate Ca₂Os₂O₇ is isostructural with orthorhombic Ca₂Nb₂O₇ and its cell parameters are: a₀ = 3.745 Å, b₀ = 25.1 Å, c₀ = 5.492 Å, Z = 4, space group Cmcm or Cmc2. Ca₂Os₂O₇ exhibits metallic conductivity and its electrical resistivity is 4.6 × 10⁻² ohm-cm at 296K.     

Kinetic study of gas-phase Lu(D3/2) with O2, N2O and CO2

The second-order rate constants of gas-phase Lu(²D_3/2) with O₂, N₂O and CO₂ from 348 to 573 K are reported. In all cases, the reactions are relatively fast with small barriers. The disappearance rates are independent of total pressure indicating bimolecular abstraction processes. The bimolecular rate constants (in molecule⁻¹ cm³ s⁻¹) are described in Arrhenius form by k(O₂)=(2.3±0.4)×10⁻¹⁰exp(−3.1±0.7 kJmol⁻¹/RT), k(N₂O)=(2.2±0.4)×10⁻¹⁰exp(−7.1±0.8 kJmol⁻¹/RT), k(CO₂)=(2.0±0.6)×10⁻¹⁰exp(−7.6±1.3 kJmol⁻¹/RT), where the uncertainties are ±2σ.     

Resonance-enhanced multiphoton ionization (REMPI) spectroscopy of photolytically generated hot CF radicals

In this paper, we investigate the rotationally resolved spectra of hot CF radicals generated after IR multiphoton dissociation (IRMPD) of CFCl₃ or CF₂Cl₂ and subsequent UV photodissociation. It is shown that these conditions are advantageous for the spectroscopy of transitions involving high rotational quantum numbers and hot bands. Thus molecular constants of CF for the first vibrationally excited state of the electronic ground state (A_v=77.1 cm⁻¹, B_v=1.389 cm⁻¹, D_v=6.570×10⁻⁶ cm⁻¹) are determined for the first time or are calculated more accurately. The spectroscopic method used was resonance-enhanced multiphoton ionization (REMPI) spectroscopy.     

Flash photolysis/temperature jump study of the vibrational relaxation of N2O(010) by O(P) and NO

This survey begins with the photochemistry at 254 nm and 298 K in the system H₂O₂COO₂RH, the primary objective of which is to determine the rate constants for the reaction OH + RH → H₂O + R relative to the well-known rate constant for the reaction OH + CO → CO₂ + H. Inherent in the scheme is that the reaction HO₂+CO→OH+CO₂ is negligible compared with the OH reaction, and a literature consensus gives k_HO2 < 10⁻¹⁹ cm³ molecule⁻¹ s⁻¹, or some 10⁶ less than k_OH at 298 K. Theoretical calculations establish that the first stage in the HO₂ reaction is the formation of a free radical intermediate HO₂ + CO → HOOCO (perhydroxooxomethyl) which decomposes to yield the products, and that the rate of formation of the intermediate is equal to the rate of formation of the products. The structure of the intermediate and a reaction profile are shown.

High temperature rate data reported subsequent to the data in the consensus and theoretical calculations lead here to a recommendation that, in the range 250–800 K, k_HO2 = 3.45 × 10⁻¹²T^1/2 exp(1.15 × 10⁴/T) cm³ molecule⁻¹ s⁻¹, the hard-sphere-collision Arrhenius modification. This yields k_HO2(298) = 1.0 × 10⁻²⁷ cm³ molecule⁻¹ s⁻¹ or some 10¹⁴ slower than k_OH(298).     

Collisional quenching of electronically excited germanium atoms, Ge[4p(S0)], by small molecules investigated by time-resolved atomic resonance absorption spectroscopy

The collisional quenching of electronically excited germanium atoms, Ge[4p²(¹S₀)], 2.029 eV above the 4p²(³P₀) ground state, has been investigated by time-resolved atomic resonance absorption spectroscopy in the ultraviolet at λ = 274.04 nm [4d(¹P₁⁰) ← 4p²(¹S₀)]. In contrast to previous investigations using the ‘single-shot mode’ at high energy, Ge(¹S₀) has been generated by the repetitive pulsed irradiation of Ge(CH₃)₄ in the presence of excess helium gas and added gases in a slow flow system, kinetically equivalent to a static system. This technique was originally developed for the study of Ge[4p²(¹D₂)] which had eluded direct quantitative kinetic study until recently. Absolute second-order rate constants obtained using signal averaging techniques from data capture of total digitised atomic decay profiles are reported for the removal of Ge(¹S₀) with the following gases (k_R in cm³ molecule⁻¹ s⁻¹, 300 K): Xe, 7.1 ± 0.4 × 10⁻¹³; N₂, 4.7 ± 0.6 × 10⁻¹²; O₂, 3.6 ± 0.9 × 10⁻¹¹; NO, 1.5 ± 0.3 × 10⁻¹¹; CO, 3.4 ± 0.5 × 10⁻¹²; N₂O, 4.5 ± 0.5 × 10⁻¹²; CO₂, 1.1 ± 0.3 × 10⁻¹¹; CH₄, 1.7 ± 0.2 × 10⁻¹¹; CF₄, 4.8 ± 0.3 × 10⁻¹²; SF₆, 9.5 ± 1.0 × 10⁻¹³; C₂H₄, 3.3 ± 0.1 × 10⁻¹⁰; C₂H₂, 2.9 ± 0.2 × 10⁻¹⁰; Ge(CH₃)₄, 5.4 ± 0.2 × 10⁻¹¹. The results are compared with previous data for Ge(¹S₀) derived in the single-shot mode where there is general agreement though with some exceptions which are discussed. The present data are also compared with analogous quenching rate data for the collisional removal of the lower lying Ge[4p²(¹D₂)] state (0.883 eV), also characterized by signal averaging methods similar to that described here.     

S2 → S0 fluorescence in an aromatic thioketone, xanthione

In addition to the red phosphorescence (T₁(³ A₂n, π^*) → S₀) xanthione exhibits in solution an emission with a maximum at ≈ 23 000 cm⁻¹ and φ_f(298°) = 5 × 10⁻³. It is shown that this emission is fluorescence from the second excited singlet state (S₂ (¹A₁ π, π^*) → S₀).     

Synthesis, crystal structure and third-order non-linear optical property of heterobimetallic cluster compound [MoOICu3S3(2,2′-bipy)2]

Nest-shaped cluster [MoOICu₃S₃(2,2′-bipy)₂] (1) was synthesized by the treatment of (NH₄)₂MoS₄, CuI, (n-Bu)₄NI, and 2,2′-bipyridine (2,2′-bipy) through a solid-state reaction. It crystallizes in monoclinic space group P2₁/n, a=9.591(2) Å, b=14.820(3) Å, c=17.951(4) Å, β=91.98(2)°, V=2549.9(10) ų, and Z=4. The nest-shaped cluster was obtained for the first time with a neutral skeleton containing 2,2′-bipy ligand. The non-linear optical (NLO) property of [MoOICu₃S₃(2,2′-bipy)₂] in DMF solution was measured by using a Z-scan technique with 15 ns and 532 nm laser pulses. The cluster has large third-order NLO absorption and the third-order NLO refraction, its ₂ and n₂ values were calculated as 6.2×10⁻¹⁰ and −3.8×10⁻¹⁷ m² W⁻¹ in a 3.7×10⁻⁴ M DMF solution.     

A tetra-nuclear copper(II) complex stabilizes an extended structure of a water nonamer: Synthesis and characterization of [Cu4(C54H46N4O14)(OH)2] · 10H2O

A tetra-nuclear copper(II) complex [Cu₄(C₅₄H₄₆N₄O₁₄)(OH)₂] · 10H₂O (1) has been synthesized starting from l-tyrosine, NaOH, 2,6-diformyl-4-methylphenol (dfp) and CuSO₄ · 5H₂O. Compound 1 crystallizes from an ethanol–water mixture in triclinic space group. In the crystal of 1, two binuclear copper units, related by a center of symmetry, are bridged by two hydroxo bridges and results in the formation of a tetra-nuclear {Cu₄} structure. Five lattice water molecules, located in the asymmetric unit, interact among themselves and form an unusual form of a water nonamer. In the crystal, the water nonamer is again hydrogen bonded to the next nonamer forming a chainlike polymer. Each {Cu₄} complex unit attaches four such water nonamer chains. Variable temperature magnetic data fit to the Bleaney–Bower’s equation with a Curie type of impurity of S = 0.5. The best fit of the magnetic data to this equation yielded 2J = −217, g = 2.019 and a TIP value of 60 × 10⁻⁶ cm³ mol⁻¹.     

High-temperature behaviour of lithium borates:: Part I: Characterization and thermal stability

Nine compounds, namely Li₃BO₃, -Li₄B₂O₅, β-Li₄B₂O₅, Li₆B₄O₉, -LiBO₂, Li₂B₄O₇, Li₃B₇O₁₂, LiB₃O₅ and Li₂B₈O₁₃ in the Li₂O–B₂O₃ system have been synthesized and characterized. The unit-cell parameters, density and solubility in water at room temperature of all the compounds are reported. The densities of the compounds were found to be in the 1.90–2.50 g cm⁻³ range, while their solubility in water at room temperature was in the 0.91–8.64×10⁻² g cm⁻³ range. Determination of the thermal stability of the compounds by quenching and differential thermal analysis (DTA) showed that only -LiBO₂ and Li₂B₄O₇ retained their original symmetry up to their congruent melting at 1121 and 1188 K, respectively, in air.     

Temperature dependence of the reaction C2H (C2D) + O2 between 295 and 700 K

The rate coefficients for the reactions of C₂H and C₂D with O₂ have been measured in the temperature range 295 K T 700 K. Both reactions show a slightly negative temperature dependence in this temperature range, with k_C2H+O2 = (3.15 ± 0.04) × 10⁻¹¹ (T/295 K)^{−(0.16 ± 0.02)} cm³ molecule⁻¹ s⁻¹. The kinetic isotope effect is k_C2H/k_C2D = 1.04 ± 0.03 and is constant with temperature to within experimental error. The temperature dependence and the C₂H + O₂ kinetic isotope effect are consistent with a capture-limited metathesis reaction, and suggest that formation of the initial HCCOO adduct is rate-limiting.