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1.
The photocurrent kinetics in acid solutions have been investigated. The diffusion coefficients of atoms H?((7±2)×10?5cm2s?1) and D?((4±1)×10?5cm2s?1) and OH? and OD? radicals ((1±0.3)×10?5cm2s?1) are found. The rate constants of capture of solvated electrons by H3O+ and D3O+ ions are identical and equal to (8±1)×109M?1s?1. From the shape of the kinetic curves it follows that electrochemical desorption of atomic hydrogen occurs from the adsorbed state. The rate constant of this process has been measured. It is shown that the rate constant of electrochemical desorption depends only slightly on the potential.  相似文献   

2.
《Chemical physics letters》1987,140(4):434-439
Emission spectra produced by 1–20 keV He+, Ne+ and H+ impact on GeF4 have been obtained and relative emission cross sections determined. By comparing the energy dependence of the ion impact data with that for charge-transfer ionization of SiF4 leading to SiF+4(D̃) and by reference to PE data of GeF4, the 255, 290 and 420 nm emissions are attributed to D̃ → Ã, B̃ and C̃ transitions, respectively of GeF+4. We found the D̃ → C̃ emission of SeF+4 in the spectral region 510 to 730 nm.  相似文献   

3.
The direct electron transfer of glucose oxidase (GOx) was achieved based on the immobilization of CdSe@CdS quantum dots on glassy carbon electrode by multi-wall carbon nanotubes (MWNTs)-chitosan (Chit) film. The immobilized GOx displayed a pair of well-defined and reversible redox peaks with a formal potential (E θ’) of ?0.459 V (versus Ag/AgCl) in 0.1 M pH 7.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (k s) of GOx confined in MWNTs-Chit/CdSe@CdS membrane were evaluated as 1.56 s?1 according to Laviron's equation. The surface concentration (Γ*) of the electroactive GOx in the MWNTs-Chit film was estimated to be (6.52?±?0.01)?×?10?11?mol?cm?2. Meanwhile, the catalytic ability of GOx toward the oxidation of glucose was studied. Its apparent Michaelis–Menten constant for glucose was 0.46?±?0.01 mM, showing a good affinity. The linear range for glucose determination was from 1.6?×?10?4 to 5.6?×?10?3?M with a relatively high sensitivity of 31.13?±?0.02 μA?mM?1?cm?2 and a detection limit of 2.5?×?10?5?M (S/N=3).  相似文献   

4.
A combined experimental and theoretical approach has been employed to establish the basicity and proton affinity of SiF4 and the structure of SiF4H+. The kinetics and energetics for the transfer of a proton between SiF4, N2, and Xe have been explored experimentally in helium at 0.35±0.02 torr and 297±3 K with a selected-ion flow tube apparatus. The results of equilibrium constant measurements are reported that provide a basicity and proton affinity for SiF4 at 297±3 K of 111.4±1.0 and 117.7±1.2 kcal mol?1, respectively. These values are more than 2.5 kcal mol?1 lower than currently recommended values. The basicity order was determined to be GB(Xe)>GB(SiF4)>GB(N2), while the proton-affinity order was shown to be PA(Xe)>PA(N2)>PA (SiF4). Ab initio molecular orbital computations at MP4SDTQ(fc)/6-311++G(3df,3pd) using geometries from B3LYP/6-31+G(d,p) indicate a value for PA(SiF4)=118.7 kcal mol?1 that is in good agreement with experiment. Also, the most stable structure of SiF4H+ is shown to correspond to a core SiF 3 + cation solvated by HF with a binding energy of 43. 9 kcal mol?1. Support for this structure is found in separate SIFT collision induced dissociation (CID) measurements that indicate exclusive loss of HF.  相似文献   

5.
A method of measuring the kinetics of currents arising at the electron photoemission from a metal into electrolyte solution when affected by the u.v. laser pulses for 10?8 s at the frequency of repetitions 10–25 Hz is described. Measurements have been taken in solutions without acceptors and in those containing N2O and NO2?, NO3? ions as electron acceptors. The rate constants of capture of the solvated electrons by N2O ((6±1)×09 mol?1 s?1) and NO2? ((4.5±1)×109 mol?1 s?1) and the diffusion coefficients of OH-radicals ((1.0±0.3)×10?5 cm2 s?1) and of NO ((1.2±0.3)×10?5 cm2 s?1) are found. The oxidation rate of NO32? has been shown to decrease from 40 cm s?1 in the range of potentials ?0.55 to ?1.0 V. The rate constant of bimolecular recombination of the solvated electrons ((1.3±0.4)×1010 mol?1 s?1) has been found from the dependence of the emitted charge on the light intensity.  相似文献   

6.
We have reported the semi conducting and photoelectrochemical properties of SrWO4 prepared by chemical route. The phase purity is confirmed by X-ray diffraction and the oxide is characterized by scanning electron microscopy, diffuse reflectance, and electrochemical impedance spectroscopy. SrWO4 crystallizes in the scheelite structure with an average crystallite size of 378 ± 6 nm. The Raman spectrum gives an intense peak at 920 cm?1 assigned to A g mode while the infrared analysis confirms the hexagonal coordination of tungsten. The UV-visible spectroscopy shows an indirect optical transition at 2.60 eV. SrWO4 exhibits n-type conduction by oxygen deficiency, confirmed by the chrono-amperometry and the intensity potential J(E) curve shows a small hysteresis. The Mott-Schottky plot gives electrons density of 5.72 × 1018 cm?3 and a flat band potential of 0.27 VSCE, indicating that the conduction band derives mainly from W6+: 6s orbital. The electrochemical impedance spectroscopy (EIS), measured in the range (1–105 Hz), shows the predominance of the bulk contribution with a dark impedance of 38 kΩ cm2. As application, the ibuprofen is degraded by electrocatalysis on SrWO4 with a conversion rate of 42%. An improvement up to 77% has been obtained by electrophotocatalysis under UV light; the conversion follows a first order kinetic with a rate constant of 2.32 × 10?4 min?1.  相似文献   

7.
The onset of micelles formations critical micelle concentration, diffusion coefficients as well as particle sizes for some new synthesized anionic copolymer surfactants PSA4a, PSA4b, and PSA4c, were determined and discussed. Three different electrochemical techniques such as cyclic voltammetry (CV), rotating disk voltammetry (RDV), and chronocoulometry (CC) were used in this investigation. The voltammetry of electroactive hydrophobic probe ferrocene solubilized surfactants was investigated in aqueous buffer carbonate solutions of pH 10. The CMC for each PSA4a, PSA4b, and PSA4c, was found to be 3.20 × 10?4, 4.60 × 10?4 and 6.30 × 10?4 M, respectively, using both CV and RDV techniques. The amount of adsorption contribution of ferrocene solubilized surfactants at the glassy carbon electrode was determined from chronocoulometric measurements and it was found in the range from (1.4 to 2.7) × 10?15 M. The apparent diffusion coefficients were estimated from RDV measurements and the real micelles diffusion coefficients were obtained. Re-quilibrium considerations of ferrocene probe kinetics at the electrode surface were treated according to two different modes of slow- and fast-kinetics. The corrected diffusion coefficient values showed constancy at (5.3 ± 0.1) × 10?7, (4.8 ± 0.1) × 10?7, and (3.6 ± 0.4) × 10?7 cm2/sec for PSA4a, PSA4b, and PSA4c, respectively in the concentration range from 20 to 200 mM. The morphological features of anionic copolymeric surfactants PSA4a, PSA4b, and PSA4c, micelles showed globular self-assembled structure.  相似文献   

8.
《Analytical letters》2012,45(12):1857-1867
Abstract

A new flexible minisensor based on MnO2/graphite/epoxy resin composite for the potentiometric determination of hydrogen peroxide was developed in this work. Under optimum experimental conditions, such as 25°C, 4 h of conditioning time in 0.1 mol L?1 NH3‐NH4 + buffer solution (pH 8.5) and a composition of 10/60/30% w/w MnO2/graphite/epoxy resin, respectively, the minisensor presented a Nernstian response for H2O2 in the concentration range from 6.0×10?7 to 1.0×10?3 mol L?1, with a slope of ?58.5±0.2 mV/pH2O2 with a detection limit of 1.6×10?8 mol L?1 H2O2. The useful lifetime of the proposed minisensor was at least 6 months (over 670 determinations for each composite), the response time was smaller than 1.5 min, and it was successfully applied in the determination of hydrogen peroxide in bleach and pharmaceutical products.  相似文献   

9.
A novel-pulsed electrolyte cathode atmospheric pressure discharge (pulsed-ECAD) plasma source driven by an alternating current (AC) power supply coupled with a high-voltage diode was generated under normal atmospheric pressure between a metal electrode and a small-sized flowing liquid cathode. The spatial distributions of the excitation, vibrational, and rotational plasma temperatures of the pulsed-ECAD were investigated. The electron excitation temperature of H Texc(H), vibrational temperature of N2 Tvib(N2), and rotational temperature of OH Trot(OH) were from 4900?±?36 to 6800?±?108 K, from 4600?±?86 to 5800?±?100 K, and from 1050?±?20 to 1140?±?10 K, respectively. The temperature characteristics of the dc solution cathode glow discharge (dc-SCGD) were also studied for the comparison with the pulsed-ECAD. The effects of operating parameters, including the discharge voltage and discharge frequency, on the plasma temperatures were investigated. The electron number densities determined in the discharge system and dc-SCGD were 3.8–18.9?×?1014?cm–3 and 2.6?×?1014 to 17.2?×?1014?cm–3, respectively.  相似文献   

10.
The ozonolysis of olefinic species is an important tropospheric process impacting on climate and human health. However, few studies have investigated these reactions as a function of temperature and even less information is available upon the effects of alkene heteroatomic substitution on the Arrhenius parameters. The electron‐withdrawing capacity of substituents about the olefinic bond strongly influences the rate of alkene ozonolysis. To understand better the effect of these substitutions, the temperature‐dependence of a series of ozone–chloroalkene reactions is investigated. Experiments were conducted in the EXTreme RAnge (EXTRA) chamber, over the range of 292–409 K and 760 Torr. The experimentally determined rate coefficients were fitted using an Arrhenius‐type analysis to yield the following activation energies: 30.80 ± 0.79, 23.18 ± 0.59, 65.2 ± 2.8, 116.9 ± 5.6, 29.5 ± 1.8, and 18.67 ± 0.96 kJ mol?1 and preexponential A‐factors 1.22+0.39?0.29×10?15, 9.3+6.7?5.4×10?16, 1.6+2.5?1.0×10?10, 6+22?3.9×10?4, 1.7+1.6?0.8×10?14, and 4.2+1.9?1.3×10?15 cm3 molecule?1 s?1 for cis‐1,2‐dichloroethene, trans‐1,2‐dichloroethene, trichloroethene, tetrachloroethene, 2‐chloropropene, and 3‐chloro‐1‐butene, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 120–129, 2011  相似文献   

11.
In this paper, self-assembled Prussian blue nanocubic particles on nanoporous glassy carbon was developed. The morphology of the PBNP-modified porous glassy carbon was characterized by scanning electron microscopy. The PBNP-GCE-red film-modified electrode was used for the sensitive detection of hydrogen peroxide. The electrochemical behavior of the resulting sensor was investigated using cyclic voltammetry and chronoamperometry. The value of α, k cat, and D was calculated as 0.35, 1.7 × 105 cm3 mol?1 s?1, and 2.6 × 10?5 cm2 s?1, respectively. The calibration curve for hydrogen peroxide determination was linear over 0–600 μM with a detection limit (S/N = 3) of 0.51 μM.  相似文献   

12.
Transient photocurrents in poly(vinyl chloride) films are shown to be due to photo-injection of electrons from metallic cathodes. Most of the injected electrons are promptly trapped, but some drift across the sample to the anode under the influence of an external electric field. The mobility of these electrons, determined by transient photoconductivity techniques, is 4.7 ± 0.5 × 10?4 cm2/V-sec at 27°C, and rises to 3.4 ± 0.5 × 10?3 cm2/V-sec at 43°C, the measuring cell having been evacuated to a pressure of 10?6 torr at both temperatures. Diffusion of helium into the samples appears to decrease the electron, mobility. It is suggested that electron transport is correctly described by using an energy-band model for intramolecular motion and an activated hopping model for intermolecular transfer. Oscillations observed in the transient photocurrents in the frequency range 103–105 Hz are attributed to electron avalanche formation at the anode, with photosuccessors.  相似文献   

13.
SiH free radicals in a dc multipole post-discharge plasma were analyzed using laser-induced fluorescence. The cross section for SiH formation from 40–70 eV electron impact induced dissociation of SiH4 was measured to be (10 ± 5) × 10?17 cm2. At the instant of its formation in its X2Π ground state, the rotational temperature of the SiH radical is 950 K. This temperature subsequently relaxes by collisions with SiH at a collisional relaxation rate k = (9 ± 2) × 1013 cm3/mole s. Quenching of the A2Δ electronic state of SiH was found to be negligible below 0.3 Torr. The primary reaction path for destruction of the SiH radical was observed to be via: SiH + SiH4 → products, k = 2 × 1012 cm3/mole s.  相似文献   

14.
Abstract

The EPR spectrum of N, N'-bis-(acetylacetone)ethylenediimino Cu(II), [Cu-en(acac)2], and N, N'-bis-(1,1,1-trifluoroacetylacetone)ethylenediimino-Cu(II), [Cu-en(tfacac)2], have been studied in doped single crystals of the corresponding Ni(II) chelate. The parameters in the usual doublet spin-Hamiltonian are found to be: Cu[en(acac)2], gz =2.183 ± 0.003, gx =2.047 ± 0.004, gy =2.048 ± 0.004, Az =204.8 × 10?4cm?1, Ax =31.5 × 10?4cm?1, Ay =27.1 × 10?4 cm?1, AzN= 12.8 × 10?4 cm?1 and AxN =AyN =14.3 × 10?4 cm?1: Cu[en(tfacac)2], gz =2.192 ± 0.002, gx =2.048 ± 0.004, gy =2.046 ± 0.004, Az =200.8 × 10?4 cm?1, Ax =31.1 × 10?4 cm?1, Ay =28.3 × 10?4 cm?1, AzN =12.8 × 10?4 cm?1 and AxN =AyN =14.6 × 10?4 cm?1. These parameters are related to coefficients in the molecular orbitals of the complex. It is found that the α-bonding is quite covalent and there is significant in-plane σ-bonding. From the nitrogen hyperfine structure it is determined that the hybridization on the nitrogen is sp2.  相似文献   

15.
《Chemical physics letters》1985,122(3):190-195
Reactions of SiF2 radicals have been studied in a fast-flow system. Rate constants at 295 K of (4.7±0.3)×10−13 cm3 molecule−1 s−1 for the reaction of SiF2 + F2, and (5.1±0.6)×10−13 cm3 molecule−1 s−1 for SiF2 + Cl2 were obtained. No reaction was observed with O2 and H2. SiF2 was detected by laser-induced fluorescence, and lifetime observations and an excitation spectrum are reported.  相似文献   

16.
Dissociative electron attachment cross-section measurements for the production of O? from CO2 have been performed utilizing a crossed target-beam—electron-beam collision geometry and a quadrupole mass spectrometer. The relative flow technique is employed to determine the absolute values of cross sections. The attachment energies corresponding to the five cross-section maxima are: 4.4 ± 0.1, 8.2 ± 0.1, 13.0 ± 0.2, 16.9 ± 0.2 and 19.4 ± 0.2 eV. The cross sections at these maxima are: 1.43 × 10?19 cm2, 4.48 × 10?19 cm2, 8.1 × 10?21 cm2, 8.1 × 10?21 cm2 and 1.2 × 10?20 cm2, respectively.  相似文献   

17.
The multiple-channel reactions Cl + Si(CH3)4 and Br + Si(CH3)4 are investigated by direct dynamics method. The minimum energy path is calculated at the MP2/6-31+G(d,p) level, and energetic information is further refined by the MC-QCISD (single-point) method. The rate constants for individual reaction channel are calculated by the improved canonical variational transition state theory with small-curvature tunneling correction over the temperature range 200–3,000 K. The theoretical three-parameter expression k 1(T) = 9.97 × 10?13 T 0.54exp(613.22/T) and k 2(T) = 1.16 × 10?17 T 2.30exp(?3525.88/T) (in unit of cm3 molecule?1 s?1) are given. Our calculations indicate that hydrogen abstraction channel is the major channel due to the smaller barrier height among feasible channels considered.  相似文献   

18.
The rate constants for proton transfer from H3+ ions to N2, O2, and CO have been measured as function of hydrogen buffer gas partial pressure. The rate constant for proton transfer from H3+ to N2 shows a very large pressure dependence, increasing from 1.0 × 10?9 cm3/s at low H2 partial pressures to 1.7 × 10?9 cm3/s at high H2 partial pressures. The rate constants for proton transfer from H3+ to O2 and CO are constant with partial pressure of H2; giving values of 6.4 × 10?10 cm3/s and 1.7 × 10?9 cm3/s, respectively. The roles of excess vibrational energy in H3+ ions and of equilibrium between forward and back reaction are discussed. Back reaction is observed only for the reaction of H3+ ions with O2, and an equilibrium constant of K = 2.0 ± 0.4 at 298 K has been determined. From these data the proton affinity of O2 is deduced to be 0.47 ± 0.11 kcal/mole higher than that of H2.  相似文献   

19.
A jet-stream kinetic technique and the resonance fluorescence method applied to detection of iodine atoms were used to measure the rate constants of the reactions of the IO· radical with the halohydrocarbons CHFCl-CF2Cl (k = (3.2 ± 0.9) × 10?16 cm3 molecule s?1) and CH2ClF (k = (9.4 ± 1.3) × 10?16 cm3 molecule s?1), the hydrogen-containing haloethers CF3-O-CH3 (k = (6.4 ± 0.9) × 10?16 cm3 molecule s?1) and CF3CH2-O-CHF2 (k = (1.2 ± 0.6) × 10?15 cm3 molecule s?1), and hydrogen iodide (k = (1.3 ± 0.9) × 10?12 cm3 molecule s?1) at 323 K.  相似文献   

20.
Single-phase samples of tungsten bronzes M x WO3 (M = K+, Rb+, Cs+) are prepared by solid-state synthesis. The reversibility of the M0.33WO3/M+-solid electrolyte interface is studied subject to the alkali metal nature and humidity over a wide temperature interval. The exchange current density at 24°C and 58%-relative humidity is 3.6 × 10?4 A/cm2 for the Rb0.33WO3/Rb+-solid electrolyte interface; 2.2 × 10?4 A/cm2 for the Cs0.33WO3/Cs+-solid electrolyte interface; and 1.3 × 10?4 A/cm2 for the K0.33WO3/K+-solid electrolyte interface. A correlation between the reversibility of the bronze|solid electrolyte interface, which is characterized by the exchange current density, and the rate of potential equilibration in sensor systems, where the bronze is a reference electrode, is revealed. Ionic component of the conductivity of the synthesized tungsten oxide bronzes is measured at a background of the predominant electronic conductivity. The ionic conductivity is three orders of magnitude lower than the electronic conductivity; it decreases in the series Rb0.33WO3 > Cs0.33WO3 > K0.33WO3, amounting to 2.3 × 10?2, 2.1 × 10?3, and 2 × 10?4 S cm?1, respectively. The working capacity of the M0.3WO3 bronzes as reference electrodes in sensor systems for carbon dioxide detection is evaluated. The plots of the cell potential vs. the CO2 concentration in the electrochemical cells are linear, their slopes (59 ± 1 mV/decade) are characteristic for one-electron process. The fastest response to changes in the CO2 concentration was obtained with the sensor system that used Rb0.33WO3 as reference electrode.  相似文献   

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