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1.
Carboxyfullerene is a class of water-soluble buckminsterfullerene with three malonic acids. Electron paramagnetic resonance (EPR) experiments are performed to examine the capacity of carboxyfullerenes to scavenge reactive oxygen species, methyl radicals and peroxyl radicals. Three types of reactions are reported: (1) reactions ofOH andO 2 with carboxyfullerenes with 5,5-dimethyl-1-pyrroline N-oxide as the trapping agent, (2) reaction ofCH3 with scavenging agents, and (3) reactions of lipid alkyl/peroxyl radicals with carboxyfullerenes. The study enables one to evaluate the efficacy of carboxyfullerene as a free-radical scavenger and an antioxidatant.  相似文献   

2.
The dissociation of photoexcited hydrogen peroxide to generate a pair of hydroxyl radicals is generally believed to take place in a repulsive electronic singlet state. The results presented here, based on time-resolved EPR experiments on the spin polarisation pattern of the acetone ketyl radical (CH3)2C?OH, generated on photodissociation of H2O2 in 2-propanol with a 248?nm laser light, strongly indicate significant involvement of a repulsive triplet state of excited hydrogen peroxide.  相似文献   

3.
The methanesulfonic acid (MSA)-diethylamine (DEA) binary liquid system is studied over the entire range of compositions at 30°C by using multiple frustrated total internal reflection IR spectroscopy. Solutions with acid: base equimolar ratio contain only 1 : 1 ion pairs. Upon adding the acid, a MSA molecule abstracts an anion from the 1 : 1 complex to produce a protonated DEA and an (H3C(O2)SO…H…OS(O2)CH3) anion with a strong H bond: (C2H5)2(H)NH+ · OS(O2)CH3 + HOS(O2)CH3 ↔ (C2H5)2(H)NH+ + (H3C(O2)SO…H…OS(O2)CH3). This equilibrium is shifted to the left. The 1 : 1 complex is present in solutions even at an significant excess of the acid. To protonate the complex, it is required at least two MSA molecules. Under conditions of an excess of the base, DEA molecules do not solvate the 1 : 1 complex. The solution separates into two phases, composed of (C2H5)2(H)NH+ · OS(O2)CH3 complexes and pure DEA.  相似文献   

4.
Thermal desorption spectrometry (TDS) and electron stimulated desorption (ESD) are employed to investigate mechanisms responsible for the formation of C2H6 in electron irradiated multilayer films of acetonitrile (CH3CN) at 30 K. Using a high sensitivity time-of-flight mass spectrometer, we observe the ESD of anionic fragments H, CH2 , CH3 and CN. Desorption occurs following dissociative electron attachment (DEA) via several negative ion resonances in the 6 to 14 eV energy range and correlates well with a “resonant” structure seen in the TDS yield of C2H6 (i.e., at mass 30 amu). It is proposed that C2H6 is formed by the reactions of CH3 radicals generated following DEA to CH3CN which also yields CN. Between 2 and 5 eV, a second resonant feature is seen in the C2H6 signal. While DEA is observed in the gas phase at these energies, no anion desorption occurs since anionic fragments likely have insufficient kinetic energy to desorb. Since the CH2 ion has not been observed in gas-phase measurements, we propose that it is formed, along with HCN (that is detected in TDS) when dissociation into CH3 and CN is hindered by adjacent molecules.  相似文献   

5.
We present in this work the direct observation of HO2 radicals after irradiation of benzene C6H6 at 248 nm in the presence of O2. HO2 radicals have been unambiguously identified using the very selective and sensitive detection of continuous wave cavity ring-down spectroscopy (cw-CRDS) coupled to a laser photolysis reactor. HO2 radicals were detected in the first vibrational overtone of the OH stretch at 6638.20 cm-1, using a DFB diode laser. This reaction might be important because 248 nm photolysis of H2O2 has often been used in the past for studying the OH-initiated degradation of C6H6, often using a large excess of C6H6 over H2O2. The possible importance of the title reaction with respect to these former laboratory studies has been quantified through comparison with HO2 signals obtained from 248 nm photolysis of H2O2: one obtains under our conditions (excess O2 and total pressure of 6.6 kPa helium) from the 248 nm irradiation of identical initial concentrations [C6H6]=[H2O2] the following relative initial radical concentrations: [HO2 ]=(0.28±0.05)×[OH]. Experiments with various O2 concentrations have revealed that the origin of the HO2 radicals is not the reaction of H-atoms with O2, but must originate from the reaction of O2 with excited C6H6 *. The quantum yield of C6H6 * formation has been deduced to ϕ=0.2±0.1. PACS  42.62.Fi; 82.20.Pm; 82.33.Tb  相似文献   

6.
A method for studying the reactions of surface alkoxy radicals with O2 at temperatures of 230 to 300 K is described. Alkoxy radicals were generated directly in the cavity of an EPR spectrometer. Surface organic radicals, prepared from paraffin wax ((CH3)2(CH2) n , n = 16–20), were applied to Aerosil particles from a solution in heptane. The Aerosil sample was placed in the cavity of the EPR spectrometer in a cylindrical cup with a central hole for pumping out gases and exposed to H atoms. In this way, it is possible observe a steady increase in the EPR signal from the surface radicals. To measure the rate constant at tropospheric temperatures, the reaction tube was placed in a Teflon jacket, through which cool nitrogen vapor was pumped. The temperature in the reactor was varied from 230 to 300 K. The recorded EPR spectra belong to the (RO) s radical. After obtaining a stable EPR signal from the surface radicals, treatment with H atoms was stopped, additional flow of O2 was introduced ([O2] = 1014–1016 cm−3), and the reaction of O2 with the surface organic radicals was studied by monitoring the EPR signal decay. The temperature dependence of the rate constant for the (RO) s + O2 → HO2 + ketone was obtained within T = 230–300 K. The extrapolation of the data to real tropospheric conditions ([O2] = 1018 cm−3) was performed.  相似文献   

7.
To extend the temperature for propane ignition to a lower region (< 680 K), ozone (O3) was used as an ignition promoter to investigate the low-temperature chemistry of propane. Ignition delay times for propane containing varying concentrations of O3 (0, 100, and 1000 ppm) were measured at 25 bar, 654–882 K, and equivalence ratios of 0.5 and 1.0 in a rapid compression machine (RCM). Species profiles during propane ignition with varying O3 concentrations were recorded using a fast sampling system combined with a gas chromatograph (GC). A kinetic model for propane ignition with O3 was developed. O3 shortened ignition delay times of propane significantly, and the NTC behavior was weakened. O atoms released from O3 reacted with propane through hydrogen abstraction reactions, which led to the fast production of OH radicals. The following oxidation of fuel radicals generated additional OH radicals. Consequently, the inhibition caused by the slow chemistry of hydrogen peroxide (H2O2) in the NTC region was weakened in the presence of O3. Experimental results with O3 addition can provide extra constraints on the low-temperature chemistry of propane. Species profiles during propane ignition at 730 K with 1000 ppm O3 addition showed the production of propanal (C2H5CHO), acetone (CH3COCH3), and acetaldehyde (CH3CHO) was promoted significantly. Model analyses indicated that O3 shifted the oxidation temperature of propane to a lower region, in which reactions of ROO radicals (NC3H7O2 and IC3H7O2) tend to generate RO radicals (NC3H7O and IC3H7O). The promotion of RO radicals led to the fast production of C2H5CHO, CH3COCH3, and CH3CHO. The corresponding species profile highlighted the reaction relevant to ROO and RO radicals (NC3H7O + O2 = C2H5CHO + HO2 and 2 IC3H7O2 = 2 IC3H7O + O2). Rate constants of these reactions were updated, which can potentially improve the performance of the core mechanism under lower temperatures and provide references for model development of larger hydrocarbons.  相似文献   

8.
Transport of exhausted thermonuclear fuel in the ITER divertor and pumping duct was modeled on a specially designed dc glow discharge setup using mass spectrometry, optical and electron microscopy, and electron probe microanalysis. Transport and deposition of hydrocarbon radicals transferred in an H2/C x H yx mixture through a hollow stainless steel anode at a total mixture pressure of 8–212 Pa and a methane content to 15 mol % were considered. It was shown that deposition of radicals and ions (CH3, C2H3, C2H5) with kinetic energies of 0.03–3 eV on the anode inner surface at 600 K was suppressed to a large extent. In the temperature range of 600–800 K, deposition of ions and radicals with kinetic energy of ~3 eV was partially restored with the formation of soft a-C:H films, while thermalized radicals were not condensed.  相似文献   

9.
Lithium trifluoromethane-sulfonate (Li-TFMS:CF3SO3Li) irradiated by γ-rays showed an electron spin resonance (ESR) powder spectrum having the rhombicg-factor ofg xx = 2.0259 ± 0.0005,g yy = 2.0112 ± 0.0005 andg zz = 2.0025 ± 0.0005 and a triplet hyperfine coupling constant ofA xx/gβ= 0.8 ± 0.15 mT.A yy andA zz are not obtained because of the broadened spectrum. The energy levels,g-factor,A xx/gβ and optical absorption spectrum of several conceivable radicals such as CF2SO3Li, CF3-S-O and CF3-S-O-O have been calculated by softwares MOPAC-V2 and Gaussian-98 based on ROHF (Restricted Hatree-Fock for open shell molecule). The most probable radical was ascribed to CF3-SO from both calculated and experimental results. The response to γ-ray dose and the thermal stability have been studied in addition to the effect of UV illumination for possible use of the signal intensity in ESR dosimetry. The obtained number of free radicals per 100 eV (G-value) was 1.23 ± 0.40.  相似文献   

10.
This paper reports on the synthesis, characterization and photophysical properties of the Tb3+ organophosphonates, TbH(O3PR)2, methylphosphonate (R=CH3), ethylphosphonate (R=C2H5), propylphosphonate (R=C3H7), and phenylphosphonate (R=C6H5). The layered Tb3+ organophosphonates were characterized by X-ray diffraction, IR spectroscopy, TG and elemental analysis. The interlayer distances of the Tb3+ organophosphonates evaluated by the X-ray diffractogram were 9.50 Å for TbH(O3PCH3)2, 12.18 Å for TbH(O3PC2H5)2, 14.84 Å for TbH(O3PC3H7)2 and 15.20 Å for TbH(O3PC6H5)2. The Tb3+ luminescence data revealed highly green emissive materials when they were excited at 368 nm, where the characteristic 5D4 → 7F J (J=6, 5, 4 and 3) transitions of Tb3+ were observed at 488, 543, 585 and 619 nm, respectively. The lifetime of the Tb3+ 5D4 → 7F5 transition (λexc=368 nm and λem=543 nm) for the Tb3+ organophosphonates was evaluated from the decay curves, which values were of 2.88, 2.22, 2.14 and 2.59 ms, respectively for TbH(O3PCH3)2, TbH(O3PC2H5)2, TbH(O3PC3H7)2 and TbH(O3PC6H5)2. TG analysis revealed that these materials are thermally highly stable, with no water molecule in their composition, which makes them potential luminophores.  相似文献   

11.
The dissociative photoionization mechanism of l-menthone has been investigated with photoionization mass spectrometry using synchrotron radiation. The adiabatic ionization energy (IE) of l-menthone and the appearance energies (AE) of its major fragment ions C9H15O+, C9H17+, C8H16+, C7H11O+, C6H10O+, C6H9O+, C5H8O+, C5H10+, C4H6O+, C5H9+, C4H8+, C4H7+, C3H7+, C3H6+, C2H2O+, and CH3+ are determined with their photoionization efficiency (PIE) spectra in the photon energy region of ∼8−15.5 eV. Breakdown diagrams identifying the major products are presented. Dissociative photoionization channels for formation of these fragment ions are proposed based on comparison of determined experimental appearance energies and energies predicted with the DFT calculations. According to our results, the experimental dissociation energies are in fair agreement with the theoretical values of the possible photodissociation channels of C10H18O.  相似文献   

12.
The photoionization and photodissociation of 1,4-dioxane have been investigated with a reflectron time-of-flight photoionization mass spectrometry and a tunable vacuum ultraviolet synchrotron radiation in the energy region of 8.0-15.5 eV. Parent ion and fragment ions at m/z 88, 87, 58, 57, 45, 44, 43, 41, 31, 30, 29, 28 and 15 are detected under supersonic conditions. The ionization energy of DX as well as the appearance energies of its fragment ions C4H7O2+, C3H6O+, C3H5O+, C2H5O+, C2H4O+, C2H3O+, C3H5+, CH3O+, C2H6+, C2H5+/CHO+, C2H4+ and CH3+ was determined from their photoionization efficiency curves. The optimized structures for the neutrals, cations, transition states and intermediates related to photodissociation of DX are characterized at the B3LYP/6-31+G(d,p) level and their energies are obtained by G3B3 method. Possible dissociative channels of the DX are proposed based on comparison of experimental AE values and theoretical predicted ones. Intramolecular hydrogen migrations are found to be the dominant processes in most of the fragmentation pathways of 1,4-dioxane.  相似文献   

13.
A detailed chemical kinetic model for oxidation of C2H4 in the intermediate temperature range and high pressure has been developed and validated experimentally. New ab initio calculations and RRKM analysis of the important C2H3 + O2 reaction was used to obtain rate coefficients over a wide range of conditions (0.003-100 bar, 200-3000 K). The results indicate that at 60 bar and medium temperatures vinyl peroxide, rather than CH2O and HCO, is the dominant product. The experiments, involving C2H4/O2 mixtures diluted in N2, were carried out in a high pressure flow reactor at 600-900 K and 60 bar, varying the reaction stoichiometry from very lean to fuel-rich conditions. Model predictions are generally satisfactory. The governing reaction mechanisms are outlined based on calculations with the kinetic model. Under the investigated conditions the oxidation pathways for C2H4 are more complex than those prevailing at higher temperatures and lower pressures. The major differences are the importance of the hydroxyethyl (CH2CH2OH) and 2-hydroperoxyethyl (CH2CH2OOH) radicals, formed from addition of OH and HO2 to C2H4, and vinyl peroxide, formed from C2H3 + O2. Hydroxyethyl is oxidized through the peroxide HOCH2CH2OO (lean conditions) or through ethenol (low O2 concentration), while 2-hydroperoxyethyl is converted through oxirane.  相似文献   

14.
Quantum-chemical analysis of electronic structure peculiarities and mossbauer spectra parameters was performed for penta-coordinated complex of ferro-protoporphyrin with imidazole (Fe(+2)PPIm). Peripheral substitutes (−CH3, −C2H3, −C2H4COOH) introduced in the porphyrin macrocycle simulated real chemical structure of protoporphyrin (PP) in heme group of Hb. Calculations displayed that doubly occupied molecular orbitals (MO) of the peripheral substitutes (−CH=CH2 and −CH2−CH2−COOH) always appeared near the occupat ion border. The orientation of vinyl fragment have the essential influence upon Fe5 dorbital populations and quadrupole splittingAEQ for5B1 and5B2 terms. The values of isomer shift were insensitive to that modification of fragment orientation.  相似文献   

15.
The reaction of C5H4RLi with FeCl2 gave nine new compounds of Fe(C5H4R)2 [R=C(CH3)2C6H4CH3-p(-m,-o), C6H10C6H5, C(Me)2C6C4OCH3-o, C6H10C6H4CH3-p(,-m,-o), C6H10C6H4OCH3-p]. The compositions of compounds were determined through elementary analysis. The structural determination was made by IR and H2NMR. Mossbauer spectia were taken at room temperature. The IS and QS values are 0.41–0.45mm/s and 2.3–2.5mm/s., respectively. The solid state structure of the complex has been determined by a single crystal x-ray diffraction study, crystal data for Fe[C5H4C(CH3)2C6H5]2: a=17.988(2)A, b=17. 411(2)A, c=7.496(1)A, α=β=90°, r=112.23°, Z=4, monoclinic form, space group C2/c. Our conclusions are: in π-acceptor ligand, the nucleophilic substituents decrease and the electrophilic substituts increase the metal to ligand electron cloud shift, which results in a decrease or an increase in the strength of the coordinate bonds and in the stabilization of the complexes by their steric effect.  相似文献   

16.
Quantum chemical calculations using density functional theory at the B3LYP level in combination with relativistic effective core potentials for the metals and TZ2P valence basis sets have been carried out for elucidating the reaction pathways of ethylene addition to MeReO2(CH2) ( C1 ). The results are compared with our previous studies of ethylene addition to OsO2(CH2)2 ( A1 ) and OsO3(CH2) ( B1 ). Significant differences have been found between the ethylene additions to the osmium compounds A1 and B1 and the rhenium compound C1 . Seven pathways for the reaction C1 +C2H4 were studied, but only the [2+2]Re,C addition yielding rhenacyclobutane C5 is an exothermic process with a high activation barrier of 48.9 kcal mol?1. The lowest activation energy (27.7 kcal mol?1) is calculated for the [2+2]Re,C addition, which leads to the isomeric form C5 ′. Two further concerted reactions [3+2]O,C, [3+2]O,O, and [2+2]Re,O and the addition/hydrogen migration of ethylene to one oxo ligand are endothermic processes which have rather high activation barriers (>35 kcal mol?1). Four isomerization processes of C1 have very large activation energies of >65 kcal mol?1. The ethylene addition to the osmium compounds A1 and B1 are much more exothermic and have lower activation barriers than the C2H4 addition to C1 . Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

17.
Electron paramagnetic resonance (EPR) spectroscopy was fruitfully used for studying the formation and the reactions of the star polysilane radical (Me3SiMe2Si)3Si (1).1, which was successfully generated both thermally and photochemically from a variety of precursors, was found to be significantly more stable kinetically than the (Me3Si)3Si radical. Thus, (Me3SiMe2Si)3Si has a half-life time of ca. 6 min at 20°C, while (Me3Si)3Si can be observed only at −25°C. Density-functional quantum-mechanical calculations show that1 and (Me3Si)3Si have the same thermodynamic stability. The high kinetic stability of1 is attributed to its backfold “umbrella”-type conformation where the β-silyl groups point “inwards” towards the radical center. This conformation protects the radical center of1 from dimerization and other reactions. The EPR spectrum of1 and in particular the Si α-hyperfine coupling constant of 5.99 mT shows that1 is less pyramidal than (Me3Si)3Si but is more pyramidal than (i-Pr3Si)3Si, with an estimated SiSiSi bond angle around the radical center of 118∘. Photolysis and thermolysis of [(Me3SiMe2Si)3Si]2 also involves the intermediacy of1. Photolysis of [(Me3SiMe2Si)3Si]2 leads to (Me3SiMe2Si)4Si, while thermolysis produced the less strained isomer of 1, (Me3SiMe2Si)3SiSi-Me2Si(Me3SiMe2Si)2SiMe3. In this study we provide the first direct evidence that silyl radicals are involved as intermediates in the reactions of silanes with di(tert-butyl)mercury.  相似文献   

18.
A Mössbauer study of two mixed-valence FeIIFeI compounds C5H5Fe(C5H4)2 FeC6(CH3)6 (1) and ¦C6(CH3)6 Fe(C5H4)2 Fe C6(CH3)6¦+ (2 +) was carried out from 4.2K to room temperature. Zero-field spectra show two types of iron atoms for1 and one type for2 +. Hence1 is a localized mixed-valence complex and2 + a delocalized mixed-valence complexe. High magnetic field spectra for 2+ give a negative sign for the EFG and show the valence electron is delocalized on the two centers. IEHT-MO calculations confirm the results and allow to explain the temperature independence of the quadrupole splitting (QS) of2 +.  相似文献   

19.
Hydrogen (H2) is known to be the fastest fuel to ignite among all practical combustion fuels. In this study, for the first time, longer ignition delay times (IDTs) for the H2 and H2 blended CH4 mixtures were measured compared to those for pure CH4. This work investigates the ignition characteristics of H2, CH4, and 50% CH4/50% H2 mixtures using a rapid compression machine at pressures ranging from 20 to 50 bar and at equivalence ratios (φ) from 0.5 to 2.0 in air in the temperature range 858–1080 K. The experimental IDTs are simulated using a newly updated kinetic mechanism, NUIGMech1.3, and good agreement is observed. At lower temperatures the IDTs of H2, CH4, and the 50% CH4/50% H2 mixtures are similar to one another, and the IDTs of the 50% CH4/50% H2 mixtures are longer than those for pure CH4 at temperatures below 930 K. At temperatures below 890–925 K, depending on the operating pressure and equivalence ratio, the hydrogen mixtures are the slowest to ignite, with IDTs being 2.5 times longer than those recorded for CH4 at a pressure of 40 bar at 890 K for φ = 1.0, and at 875 K for φ = 2.0. At low temperatures alkyl (Ṙ = ĊH3 and Ḣ) radicals add to O2 producing RȮ2 radicals, which then react with HȮ2 radicals forming ROOH (H2O2 and CH3OOH) and O2. For H2, the self-recombination of HȮ2 radicals leads to chain propagation which inhibits reactivity, whereas for CH4, the reaction between RȮ2 (CH3OȮ) and HȮ2 leads to chain branching, increasing reactivity. Furthermore, CH3OOH decomposes more easily to produce CH3Ȯ and ȮH radicals than does H2O2 to produce two ȮH radicals. Thus, mixtures containing higher H2 concentrations are slower to ignite compared to those with higher CH4 concentrations at low temperatures.  相似文献   

20.
Symmetrical (RCO2CO2R; R = XCH2CH2) and asymmetrical (RCO2CO2R′; R = C9H19CH2CH2, R′ = CH3 or m‐ClC6H4) primary diacyl peroxides were thermally decomposed under different conditions to analyze the decarboxylation rates of the thermally generated acyloxy radicals. Quantitative models of the geminate product yields, and qualitative and quantitative 1H‐CIDNP spectroscopy were used to obtain the decarboxylation rate estimates. Results reported here suggest that, unlike short chain acyloxy radicals such as propanoyloxyl, long chain acyloxy radicals possess the highest decarboxylation rates of all known acyloxy radicals, estimated at (0.5–1.5) × 1012 s?1 between 80 and 140 °C. Given the nature of the dissociative state of acyloxy radicals, such rates appear to be the result of destabilization of the former by the steric bulk of the long chain substituents. Additionally, the rate of this order of magnitude suggests a nearly concerted decarboxylation of primary diacyl peroxides. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

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