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1.
The kinetics of the reaction of the CH3CHBr, CHBr2 or CDBr2 radicals, R, with HBr have been investigated in a temperature-controlled tubular reactor coupled to a photoionization mass spectrometer. The CH3CHBr (or CHBr2 or CDBr2) radical was produced homogeneously in the reactor by a pulsed 248 nm exciplex laser photolysis of CH3CHBr2 (or CHBr3 or CDBr3). The decay of R was monitored as a function of HBr concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature. The reactions were studied separately from 253 to 344 K (CH3CHBr + HBr) and from 288 to 477 K (CHBr2 + HBr) and in these temperature ranges the rate constants determined were fitted to an Arrhenius expression (error limits stated are 1σ + Student’s t values, units in cm3 molecule−1 s−1, no error limits for the third reaction): k(CH3CHBr + HBr) = (1.7 ± 1.2) × 10−13 exp[+ (5.1 ± 1.9) kJ mol−1/RT], k(CHBr2 + HBr) = (2.5 ± 1.2) × 10−13 exp[−(4.04 ± 1.14) kJ mol−1/RT] and k(CDBr2 + HBr) = 1.6 × 10−13 exp(−2.1 kJ mol−1/RT). The energy barriers of the reverse reactions were taken from the literature. The enthalpy of formation values of the CH3CHBr and CHBr2 radicals and an experimental entropy value at 298 K for the CH3CHBr radical were obtained using a second-law method. The result for the entropy value for the CH3CHBr radical is 305 ± 9 J K−1 mol−1. The results for the enthalpy of formation values at 298 K are (in kJ mol−1): 133.4 ± 3.4 (CH3CHBr) and 199.1 ± 2.7 (CHBr2), and for α-C–H bond dissociation energies of analogous compounds are (in kJ mol−1): 415.0 ± 2.7 (CH3CH2Br) and 412.6 ± 2.7 (CH2Br2), respectively. 相似文献
2.
A column method has been established for the preconcentration of aluminum and copper(II) with Alizarin Red S and a cetyltrimethylammonium-perchlorate ion pair supported on naphthalene, using a simple glass-tipped tube. Aluminum and copper(II) react with Alizarin Red S to form water-soluble colored chelate anions. These chelate anions form water-insoluble ternary complexes with the adsorbent on the inactive surface of naphthalene packed into a column. They are quantitatively retained in the pH ranges of 4.7-5.2 for aluminum and 5.0-10.0 for copper. The solid mass is dissolved out from the column with 5 ml of dimethylformamide (DMF) for aluminum and 5 ml of ethanol for copper and the absorbance was measured with a spectrometer at 525 nm for aluminum and at 529 nm for copper. The calibration curves were linear over the concentration ranges of 0.25-5.0 μg of aluminum in 5 ml of DMF solution and 0.50-12.0 μg of copper in 5 ml of ethanol solution. The molar absorptivities and Sandell′s sensitivities were respectively calculated to be 2.8 × 104 liter · mol−1 · cm−1 and 9.62 × 10−4 μg · cm−2 for aluminum and 2.5 × 104 liter · mol−1 · cm−1 and 2.5 × 10−3 μg · cm−2 for copper. Seven replicate determinations of sample solutions containing 2.5 μg of aluminum and 6.0 μg of copper gave mean absorbances of 0.520 and 0.480 with relative standard deviations of 1.67 and 0.33%, respectively. Interference due to various foreign ions has been studied and the method has been applied to the determination of aluminum in standard alloys, tea leaves, vehicle particulates, copper in coal fly ash, and commercial salt samples. 相似文献
3.
The optimum conditions for the formation of ternary lead complexes with Pyrocatechol Violet and cationic surfactants have been evaluated. The examined ternary systems form a basis for simple and sensitive spectrophotometric methods for lead (ε = 4.20−5.06 × 104 liters · mol−1 · cm−1). Using the most sensitive method, lead content in zinc powder has been determined. Lead does not form ternary complexes with the other triphenylmethane reagents, Chrome Azurol S and Eriochrome Cyanine R, in the presence of cationic surfactants because of its too “soft” properties. 相似文献
4.
R. Plasil I. Korolov T. Kotrik J. Glosik 《International journal of mass spectrometry》2008,275(1-3):80-85
Recombination rate coefficients of protonated and deuterated ions KrH+, KrD+, XeH+ and XeD+ were measured using Flowing Afterglow with Langmuir Probe (FALP). Helium at 1600 Pa and at temperature 250 K was used as a buffer gas in the experiments. Kr, Xe, H2 and D2 were introduced to a flow tube to form the desired ions. Because of small differences in proton affinities of Kr, D2 and H2 mixtures of ions, KrD+/D3+ and KrH+/H3+ are formed in the afterglow plasma, influencing the plasma decay. To obtain a recombination rate coefficient for a particular ion, the dependencies on partial pressures of gases used in the ion formation were measured. The obtained rate coefficients, αKrD+(250 K) = (0.9 ± 0.3) × 10−8 cm3 s−1 and αXeD+(250 K) = (8 ± 2) × 10−8 cm3 s−1 are compared with αKrH+(250 K) = (2.0 ± 0.6) × 10−8 cm3 s−1 and αXeH+(250 K) = (8 ± 2) × 10−8 cm3 s−1. 相似文献
5.
Gamil A. Guirgis Todor K. Gounev Pengqian Zhen James R. Durig 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》1999,55(14):2753
The infrared (3500–40 cm−1) spectra of gaseous and solid 1-fluoro-1-methylsilacyclobutane, c-C3H6SiF(CH3), have been recorded. Additionally, the Raman spectrum (3500–30 cm−1) of the liquid has been recorded and quantitative depolarization values have been obtained. Both the axial and equatorial (with respect to the methyl group) conformers have been identified in the fluid phases. Variable temperature (−55–−100°C) studies of the infrared spectra of the sample dissolved in liquid xenon have been carried out. From these data, the enthalpy difference has been determined to be 267±10 cm−1 (3.19±0.12 kJ mol−1), with the axial conformer being the more stable form and the only conformer remaining in the polycrystalline solid. A complete vibrational assignment is proposed for the axial conformer and many of the fundamentals for the equatorial conformer have also been identified. The vibrational assignments are supported by normal coordinate calculations utilizing ab initio force constants. Complete equilibrium geometries have been determined for both rotamers by ab initio calculations employing the 6-31G* and 6-311++G** basis sets at the levels of restricted Hartree–Fock (RHF) and/or Moller–Plesset (MP) to second order. The results are discussed and compared to those obtained for some similar molecules. 相似文献
6.
Wenhe Gong H. Yun Y. B. Ning J. E. Greedan W. R. Datars C. V. Stager 《Journal of solid state chemistry》1991,90(2)
The grossly nonstoichiometric perovskites SrTiO3−x with x = 0.28, 0.17, and 0.08 were prepared from a reaction of Sr2TiO4, TiO, and TiO2 at 1500°C. For x = 0.28 relatively large single crystals were obtained. Also for this sample the crystal symmetry was found to depend on the rate of cooling from the reaction temperature and the annealing conditions. Rapidly cooled samples are tetragonal a = 3.9177(3) Å, c = 3.8878(5) Å. Samples annealed in vacuum at temperatures of 1000 to 600°C are cubic a = 3.9075(3) Å with no change in cell volume. Single crystal data from a tetragonal sample indicate slight preferential occupancy of one oxygen position in P4/mmm. No evidence for any supercell due to defect ordering could be seen by TEM in either cubic or tetragonal samples. The x = 0.28 crystals show metallic resistivity, (300 K) = 6 × 10−4 ohm-cm and temperature-independent paramagnetism, χm = 118 × 10−6 cm3 mole−1. Hall effect data from 300 to 4.2 K analyzed on a single carrier model give a temperature-independent n-type carrier density of 2.4 × 1021 cm−3. This is a factor of 3.9 less than that expected if the creation of each oxygen vacancy results in the production of two carriers in a single band. Hall data for x = 0.17 and 0.08 samples give similar results corresponding to densities of 2.1 and 1.4 × 1021 cm−3, respectively, in the same temperature range. These densities are 2.7 and 1.9 times less than the expected single-band value, respectively. Such results point to a two-band model with a large effective mass in one of the bands. 相似文献
7.
A simple and sensitive procedure for Spectrophotometric determination of exchangeable magnesium has been developed. At 0.15 – 0.375 N ammonia, magnesium reacts with xylidyl Blue I in the presence of CTAB to form a colored ternary complex, which has an absorption maximum at 524 nm. The molar absorption coefficient is 2.2 × 104 liters · mol−1 · cm−1. The Beer rule will be valid for concentrations from 0 to 8 μg/20 ml magnesium. The method has been used for rapid determination of microgram amounts of exchangeable magnesium in acidic soil with good reproducibility. 相似文献
8.
Layered crystalline zirconium phenylphosphonate, Zr(O3PC6H5)2, changed its interlamellar distance of 1481 pm after intercalation of n-alkylmonoamines, CH3---(CH2)n---NH2 (n=0–6). The infrared spectra of the precursor host and the corresponding intercalated compounds presented vibrations associated with PO3 groups in the 1163–1039 cm−1 range and additional bands related to C---H stretching bands in the 2950–2850 cm−1 interval were observed after amine insertion. The thermogravimetric curves showed a mass loss assigned to the phenyl group; however, the amine intercalated fraction was not quantitatively determined. A peak in the 31P NMR spectrum centered at −6 ppm for the host was observed. The surface area was 42.0±0.2 m2 g−1 and the scanning electron micrograph gave images consistent with lamellar structural features. The layered compound was calorimetrically titrated with amine in ethanol, requiring three independent operations: (i) titration of matrix with amine, (ii) matrix salvation, and (iii) dilution of the amine solution. From those thermal effects the variation in enthalpy was calculated as: −41±1.00,−33.28±0.50,−34.40±0.80,−10.40±0.40,−12.40±0.42,−16.10±0.08 and −7.0±0.04 kJ mol−1, for n=0–6, respectively. The exothermic enthalpic values reflected a favorable energetic process of amine–host intercalation in ethanol. The negative Gibbs free energy results supported the spontaneity of all these intercalation reactions. The positive favorable entropic values, as carbon chain size increased, are in agreement with the free solvent molecules in the medium, as the amines are progressively bonded to the crystalline lamellar inorganic matrix at the solid/liquid interface. 相似文献
9.
A Raman spectroscopic determination of the kinetics of decomposition of ammonium chromate (NH4)2CrO4
Raman spectroscopy was used as a method in the kinetic investigation of the thermal decomposition of solid (NH4)2CrO4. Time-dependent measurements of the intensity of the totally symmetric stretching Cr---O mode of (NH4)2CrO4 have been made between 343 and 363 K. A short initial acceleratory period is observed at lower temperatures and the decomposition reaction decelerates after the maximum decomposition rate has been reached at all temperatures. These results can be interpreted in terms of the Avrami-Erofe'ev law 1 − (χr)1/2 = kt, where χr is the fraction of reactant at time t. At 358 K, k is equal to 1.76 ± 0.01 × 10−3 sec−1 for microcrystals and for powdered samples. Activation energies of 97 ± 10 and 49 ± 0.9 kJ mole−1 have been calculated for microcrystalline and powdered samples, respectively. 相似文献
10.
The diffusion of strontium and zirconium in single crystal BaTiO3 was investigated in air at temperatures between 1000 °C and 1250 °C. Thin films of SrTiO3, deposited by spin coating a precursor solution and thin films of zirconium, deposited onto the sample surfaces by sputtering, were used as diffusion sources. The diffusion profiles were measured by SIMS depth profiling on a time-of-flight secondary ion mass spectrometer (ToF-SIMS). The diffusion coefficients of strontium and zirconium were given by DSr = 3.6 × 102.0±4.4 exp[−(543 ± 117) kJ mol−1/(RT)] cm2 s−1 and DZr = 1.1 × 101.0±2.1 exp[−(489 ± 56) kJ mol−1/(RT)] cm2 s−1. The results are discussed in terms of different diffusion mechanisms in the perovskite structure of BaTiO3. 相似文献
11.
Sun Yi 《Microchemical Journal》1987,36(3)
A spectrophotometric study of the Cd(II) and Cu(II) complex of a new reagent, 2-(5-bromo-2-pyridylazo)-5-diethylamino phenol (5-Br-PADAP) in the presence of polyglycol octylphenyl ether (OP) is presented. A reddish binary complex is formed at pH 9 and shows maximal absorbance at 560 nm with molar absorptivity of 1.16 × 105 · mol−1 · cm−1 liter (Cd), 1.5 × 105 mol−1 · cm−1 · liter (Cu). Beer's law is followed over the range 0.0 to 20 μg cadmium(II) and 0.0–18 μg copper(II). The continuous variation method and molar ratio method showed that the metal ligand ratio is 1:2; ordinarily, most ions do not interfere with the determination and the method can be applied for direct spectrophotometric determination of cadmium(II) and copper(II) in actual samples and the results obtained are satisfactory. 相似文献
12.
Erika Famini Silva Robson Pacheco Pereira Ana Maria Rocco 《European Polymer Journal》2009,45(11):3127-3137
In the present work, blends of poly(ethylene oxide) (PEO), poly(acrylonitrile-co-methyl acrylate) (PANMA) and poly(4-vinylphenol-co-2-hydroxyethyl methacrylate) (PVPh-HEM) were studied by DSC, FTIR and electrochemical impedance spectroscopy (EIS). PEO/PANMA blends were found to be immiscible, while PEO/PVPh-HEM blends are miscible and PVPh-HEM/PANMA exhibits partial miscibility behaviour. The ternary PEO/PANMA/PVPh-HEM blends exhibited miscible compositions for PVPh-HEM and PEO-rich systems. The miscibility observed is a direct consequence of the hydrogen bond interactions among the polymer chains, in which the phenol groups in PVPh-HEM interact with both PEO and PANMA chains. The proton conductivity of a selected membrane based on the ternary blend containing 60% PEO and doped with H3PO4 aqueous solution reached 8 × 10−3 Ω−1 cm−1 at room temperature and 3 × 10−2 Ω−1 cm−1 at 80 °C. 相似文献
13.
A sensitive spectrophotometric method for the determination of copper(II) based on a ternary complex with chromal blue G, a triphenylmethane reagent in the presence of cetyltrimethylammonium chloride, is described. The sensitivity of color reaction between copper and chromal blue G has been greatly increased by the sensitizing action of cetyltrimethylammonium chloride, a cationic surfactant. The color development of the ternary complex can be utilized in the highly sensitive spectrophotometric determination of copper. The molar absorptivity of the binary complex between copper and chromal blue G ε630nm = 9.56 × 103liters · mol−1 · cm−1 is enchanced on ternary complex formation to ε542 nm = 4.78 × 104liters · mol−1 · cm−1. The ternary complex gave a maximal absorbance at 542 nm in the pH range 9.8–11. Beer's law is obeyed up to at least 1.2 ppm of copper. The maximal absorbance of the ternary complex was found to develop within 5 min and then it remains constant for several hours. The formation constant of the ternary complex is calculated to be 8.6 × 1010 under these conditions. 相似文献
14.
I. Korolov R. Plasil T. Kotrik P. Dohnal J. Glosik 《International journal of mass spectrometry》2009,280(1-3):144
Recombination of HCO+ and DCO+ ions with electrons was studied in afterglow plasma. The flowing afterglow with Langmuir probe (FALP) apparatus was used to measure the recombination rate coefficients and their temperature dependencies in the range 150–270 K. To obtain a recombination rate coefficient for a particular ion, the dependencies on partial pressures of gases used in the ion formation were measured. The variations of αHCO+(T) and αDCO+(T) seem to obey the power law: αHCO+(T) = (2.0 ± 0.6) × 10−7 (T/300)−1.3 cm3 s−1 and αDCO+(T) = (1.7 ± 0.5) × 10−7 (T/300)−1.1 cm3 s−1 over the studied temperature range. 相似文献
15.
Dynamical spin chirality of α-glycine crystal at 301−302 K was investigated by DC (direct current)-magnetic susceptibility measurement at temperatures ranging from 2 to 315 K under the external magnetic fields (H=±1 T) parallel to the b axis. The α-glycine crystallizes in space group P21/n with four molecules in a cell, which has centrosymmetric charge distribution. The bifurcated hydrogen bonds N+(3)−H(8)···O(1) and N+(3)−H(8)···O(2) are stacked along the b axis with different bond intensities and angles, which form anti-parallel double layers. Atomic force spectroscopy result at 303 K indicated that the surface molecular structures of α-glycine formed a regular flexuous framework in the b axis direction. The strong temperature dependence is related to the reorientation of NH3+ group and the electron spin flip-flop of (N+H) mode. Under the opposite external magnetic field of 1 T and −1 T, the electron spins of N+(3)−H(8)···O(1) and N+(3)−H(8)···O(2) flip-flop at 301−302 K. These results suggested a mechanism of the magnetoelectric effect based on the dynamical spin chirality of (N+H), which induced the electric polarization to produce the onset of pyroelectricity of α-glycine around 304 K. 相似文献
16.
Tetraethylenepentaamineheptaacetic acid (TPHA) combines with cerium(IV) to form an intensely yellow chelate having a molar absorptivity of 4.5 × 104 mol−1 · cm−1 · liter at 304 nm. The chelate contains 1 mol of TPHA coordinated to a cerium(IV) atom. Beer's law is followed from 0.05 to 0.5 ppm cerium (1.00-cm cells). Of many ions tested at the 1-ppm level and the 100-ppm concentration, only iron(III) produces little interference. 相似文献
17.
T. J. Wallington H. Egsgaard O. J. Nielsen J. Platz J. Sehested T. Stein 《Chemical physics letters》1998,290(4-6)
Pulse radiolysis transient UV–visible absorption spectroscopy was used to study the UV–visible absorption spectrum (225–575 nm) of the phenyl radical, C6H5(), and kinetics of its reaction with NO. Phenyl radicals have a strong broad featureless absorption in the region of 225–340 nm. In the presence of NO phenyl radicals are converted into nitrosobenzene. The phenyl radical spectrum was measured relative to that of nitrosobenzene. Based upon σ(C6H5NO)270 nm=3.82×10−17 cm2 molecule−1 we derive an absorption cross-section for phenyl radicals at 250 nm, σ(C6H5())250 nm=(2.75±0.58)×10−17 cm2 molecule−1. At 295 K in 200–1000 mbar of Ar diluent k(C6H5()+NO)=(2.09±0.15)×10−11 cm3 molecule−1 s−1. 相似文献
18.
The basic copper arsenate mineral strashimirite Cu8(AsO4)4(OH)4·5H2O from two different localities has been studied by Raman spectroscopy and complemented by infrared spectroscopy. Two strashimirite mineral samples were obtained from the Czech (sample A) and Slovak (sample B) Republics. Two Raman bands for sample A are identified at 839 and 856 cm−1 and for sample B at 843 and 891 cm−1 are assigned to the ν1 (AsO43−) symmetric and the ν3 (AsO43−) antisymmetric stretching modes, respectively. The broad band for sample A centred upon 500 cm−1, resolved into component bands at 467, 497, 526 and 554 cm−1 and for sample B at 507 and 560 cm−1 include bands which are attributable to the ν4 (AsO43−) bending mode. In the Raman spectra, two bands (sample A) at 337 and 393 cm−1 and at 343 and 374 cm−1 for sample B are attributed to the ν2 (AsO43−) bending mode. The Raman spectrum of strashimirite sample A shows three resolved bands at 3450, 3488 and 3585 cm−1. The first two bands are attributed to water stretching vibrations whereas the band at 3585 cm−1 to OH stretching vibrations of the hydroxyl units. Two bands (3497 and 3444 cm−1) are observed in the Raman spectrum of B. A comparison is made of the Raman spectrum of strashimirite with the Raman spectra of other selected basic copper arsenates including olivenite, cornwallite, cornubite and clinoclase. 相似文献
19.
A flow injection on-line coprecipitation preconcentration system with diethyldithiocarbamate (DDTC) chelate of copper used as the coprecipitate carrier was coupled with flame atomic absorption spectrometry (FAAS) for the determination of trace silver. Silver was on-line coprecipitated with DDTC-Cu(II) in 0.5 moL · L−1HCl, and the precipitate was collected in a knotted reactor. The precipitate was then dissolved by isobutyl methyl ketone and transported directly into the nebulizer–burner system of a flame atomic absorption spectrometer. A detection limit (3ς) of 0.6 μg · L−1was achieved for a loading period of 30 s, a relative standard derivation of 2.0% was obtained for 11 determinations of 20 μg · L−1Ag(I). Interference-free levels were 10 mg · L−1for Cd2+, 50 mg · L−1for Cu2+, 50 mg · L−1for Mn2+, 25 mg · L−1for Ni2+, 100 mg · L−1for Pb2+, 50 mg · L−1for Zn2+, 500 mg · L−1for Fe3+, and 2000 mg · L−1for Fe2+reduced from Fe3+by ascorbic acid. The developed method has been successfully applied to the determination of trace amount of silver in geological samples. 相似文献
20.
Titanium (IV) forms a yellow-colored chelate with 5,5′-thiodisalicylic acid, whose sensibility is pD = 6.1 between pH 4 and 6. The stoichiometry of the complex formed is 1:1 at pH 0.5. The system follows Beer's law at pH 4.9 (λ = 385 nm) over the concentration range 0.6–3.2 ppm (ε = 16000 liters · mol−1 · cm−1). The method can be suitably used for determination of titanium in plants. 相似文献