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Arrhenius parameters for the reaction of hydrogen atoms with azide and thiocyanate in aqueous solution have been determined using electron pulse radiolysis and electron paramagnetic resonance free induction decay attenuation measurements. Absolute values for SCN-, N3(-), and HN3 were well-described over the temperature range of 9-81 degrees C by the equations log k5 = (12.03 +/- 0.12) - [(21.05 +/- 0.66 kJ mol(-1))/2.303RT], log k10 = (12.75 +/- 0.21) - [(18.43 +/- 1.22 kJ mol(-1))/2.303RT], and log k15 = (11.59 +/- 0.12) - [(21.44 +/- 0.69 kJ mol(-1))/2.303RT], corresponding to room temperature (22 degrees C) rate constants of (2.07 +/- 0.03) x 10(8), (3.15 +/- 0.08) x 10(9), and (6.31 +/- 0.05) x 10(7) M(-1) s(-1) and activation energies for these chemicals of 21.05 +/- 0.66, 18.4 +/- 1.2, and 21.44 +/- 0.69 kJ mol(-1), respectively. The similarity of these three measured activation energies, taken together with the available information on reaction products, suggests a similar reaction mechanism, which is proposed to be an initial hydrogen atom adduct formation in these molecules, followed by single bond breakage. 相似文献
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Dr. Jacy K. Conrad Prof. Aliaksandra Lisouskaya Prof. Stephen P. Mezyk Prof. David M. Bartels 《Chemphyschem》2023,24(24):e202300465
The reactivity of chromium(III) species with the major oxidizing and reducing radiolysis products of water was investigated in aqueous solutions at temperatures up to 150 °C. The reaction between the hydrated electron (eaq−) and Cr(III) species showed a positive temperature dependence over this temperature range. The reaction was also studied in pH 2.5 and 3.5 solutions for the first time. This work also studied the reaction between acidic Cr(III) species and the hydroxyl radical (⋅OH). It was found that Cr3+ did not react significantly with the ⋅OH radical, but the first hydrolysis species, Cr(OH)2+, did with a rate coefficient of k= (7.2±0.3)×108 M−1 s−1 at 25 °C. The oxidation of Cr(OH)2+ by the ⋅OH radical formed an absorbing product species that ultimately oxidized to give Cr(VI). These newly measured reaction rates allow for the development of improved models of aqueous chromium speciation for the effective remediation of liquid high-level nuclear waste via vitrification processes. 相似文献
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Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films
We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La0.7Ca0.3MnO3 (LCMO) and YBa2Cu3O7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO3 (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on
the LAO (control) and LCMO side of the substrate. Critical current, I
c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed
that while the control side showed a J
c of ∼ 2 × 106 A/cm2, the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J
c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of
J
c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection
length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length
has been quantified. A control experiment carried out with LaNiO3 deposited by PLD on YBCO did not show any evidence of self-injection. 相似文献
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Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film
La0.67Ba0.33MnO3 (LBMO) thin film is deposited on a 36.7°C SrTiO3 bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics
are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial
magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears
at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic
conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese
atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance
with the increase in temperature is due to enhanced spin-flip scattering process. 相似文献
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Molar extinction coefficients of some carbohydrates viz. l-arabinose (C5H10O5), d-glucose (C6H12O6), d-mannose (C6H12O6), d-galactose (C6H12O6), d(-) fructose (C6H12O6) and maltose (C12H24O12) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a
narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter
polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying
within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well. 相似文献
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Mezyk SP Neubauer TJ Cooper WJ Peller JR 《The journal of physical chemistry. A》2007,111(37):9019-9024
Absolute rate constants and degradation efficiencies for hydroxyl radical and hydrated electron reactions with four different sulfa drugs in water have been evaluated using a combination of electron pulse radiolysis/absorption spectroscopy and steady-state radiolysis/high-performance liquid chromatography measurements. For sulfamethazine, sulfamethizole, sulfamethoxazole, and sulfamerazine, absolute rate constants for hydroxyl radical oxidation were determined as (8.3 +/- 0.8) x 10(9), (7.9 +/- 0.4) x 10(9), (8.5 +/- 0.3) x 10(9), and (7.8 +/- 0.3) x 10(9) M(-1) s(-1), respectively, with corresponding degradation efficiencies of 36% +/- 6%, 46% +/- 8%, 53% +/- 8%, and 35% +/- 5%. The reduction of these four compounds by their reaction with the hydrated electron occurred with rate constants of (2.4 +/- 0.1) x 10(10), (2.0 +/- 0.1) x 10(10), (1.0 +/- 0.03) x 10(10), and (2.0 +/- 0.1) x 10(10) M(-1) s(-1), respectively, with efficiencies of 0.5% +/- 4%, 61% +/- 9%, 71% +/- 10%, and 19% +/- 5%. We propose that hydroxyl radical adds predominantly to the sulfanilic acid ring of the different sulfa drugs based on similar hydroxyl radical rate constants and transient absorption spectra. In contrast, the variation in the rate constants for hydrated electrons with the sulfa drugs suggests the reaction occurs at different reaction sites, likely the different heterocyclic rings. The results of this study provide fundamental mechanistic parameters, hydroxyl radical and hydrated electron rate constants, and degradation efficiencies that are critical for the evaluation and implementation of advanced oxidation processes (AOPs). 相似文献
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de Alwis SP 《Physical review D: Particles and fields》1992,46(12):5429-5438
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