首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
The deposition velocity of gaseous organic129I species from the exhaust air stack of the Karlsruhe reprocessing plant onto pasture grass was measured by a field experiment. By simultaneously measuring the amount of129I deposited per unit area of pasture grass and the time integrated mean air concentration of129I a deposition velocity of Vg=5.8×10–1 /cm s–1/ onto pasture grass was determined.  相似文献   

2.
The polarographic behaviour of 2-nitronaphthalene was investigated by DC tast polarography (DCTP) and differential pulse polarography (DPP), both at a dropping mercury electrode, and differential pulse voltammetry and adsorptive stripping voltammetry, both at a hanging mercury drop electrode. Optimum conditions have been found for the determination of 2-nitronaphthalene by the given methods in the concentration ranges of 2×10–6–1×10–4, 2×10–7–1×10–4, 1×10–8–1×10–4 and 2×10–9–1×10–8 M, respectively. Practical applicability of these techniques was demonstrated by the determination of 2-nitronaphthalene in drinking and river water after its preliminary separation and preconcentration using liquid–liquid and solid-phase extraction with limits of determination of 3×10–10 M (drinking water) and 3×10–9 M (river water).  相似文献   

3.
Pulsed Corona Discharge-Induced Reactions of Acetophenone in Water   总被引:2,自引:0,他引:2  
The reactions of acetophenone in water by pulsed corona discharges have been investigated to provide fundamental information concerning the reactions of acetophenone in water. Experimental results indicated that photolysis of acetophenone did not involve a hydroxyl radical mechanism and the majority flux of hydroxyl radicals originated from the dissociation of gas-phase oxygen in the plasma channels. The rate constants for photolysis and pyrolysis were determined to be 1.5×10–7 M-s–1, 2.2×10–4 s–1, respectively. The rate constant for the oxidative reactions was measured as 1.2×10–7 M-s–1. Results from this study support the proposal that acetophenone degradation reaction proceed through the oxidative reaction pathway, where molecular oxygen accelerates acetophenone degradation, photolysis, and pyrolysis pathways.  相似文献   

4.
The kinetics of the transfer of Erythrosine B dianions (EB2–) and Eosin Y dianions (EY2–) across the 1,2-dichloroethane|water interface, studied using ac-modulated voltfluorometry, is compared with that of Rose Bengal dianions (RB2–). All three exhibit anomalous phase angles, showing the transient adsorption of these ions at the interface. The apparent standard rate constants are 9.0 × 10–3 and 1.3 × 10–2 cm s–1 for EY2– and EB2– at 25° (cp. 1.4 × 10–2 cm s–1 for RB2–). The slight decrease in the rate in the order RB2–, EB2–, and EY2– may be associated with the increasing polarity of the ions, which endows the ions with a stronger interaction with water, resulting in the slower rotational dynamics of the ions on crossing the interface.  相似文献   

5.
Summary Organochromium complexes, [CrRL(H2O)]2+] (L = 1,4,8,12-tetraazacyclopentadecane; R = 1°- or 2°-alkyl, or para-substituted benzyl), are oxidized to [CrRL(H2O)]3+, which rapidly decomposes (k 3 > 102 s–1) by homolysis of the Cr-C bond. Rate constants of the oxidation of these complexes by [IrCl6]2– range from 2.20 × 10–1 (R = Me) to 4.60 × 105 (R = 4-MeC6H4CH2)dm3 mol–1 s–1. A very negative reaction constant (–4.3) is found for the oxidation of para-substituted benzlchromium(III) complexes which, in conjunction with the results of product analysis, indicates a [CrIII/R.] type transition state.  相似文献   

6.
An attempt was made to detect neutrons from the so-called cold nuclear fusion of deuterium in palladium and titanium, both saturated with deuterium: the palladium electrolytically and the titanium from gas phase. The measurements were performed in a tunnel located 30 m deep in limestone, using3He filled proportional counters surrounded by water for neutron moderation. In all cases the detected neutron flux was practically equal to the background level. Very low upper limits to the neutron source strength were obtained from this experiment: 2×10–4 n.s–1g–1 Pd and 4.3×10–4 n.s–1g–1 Ti on the 1 level.  相似文献   

7.
An electroanalytical study of the herbicide propazine's reduction process in micellar solutions and oil-in-water emulsions is reported. The anionic surfactant sodium pentanesulphonate was chosen as the most suitable. The differential pulse polarograms of micellar solutions had two reduction peaks below pH 2.0, whereas only one peak was obtained above pH 2.O. Ethyl acetate was chosen as the organic solvent to form propazine emulsions. Unlike in micellar solutions, the DPP polarograms of propazine emulsions showed only one peak even at pH < 2.0, suggesting that propazine hydrolysis was hindered in the emulsified medium. The limiting current is diffusion-controlled and the electrode process is irreversible. Propazine can be determined by differential pulse polarography over the 1.0 × 10–1 – 1.0 × 10–1moll–1 and 1.0 × 10–15 – 4.0 × 10–1 moll–1 concentration ranges and the limit of detection was 2.8 × 10–1 moll–1. Of the potential interferents simazine, methoprotryne and terbutryn (alls-triazines), thiram (a dithiocarbamate), dinoseb (nitrophenolic), and heptachlor (chlorinated cyclo-diene herbicide), only the first two were significant (10% error for equimolar concentrations). The method was applied to the determination of propazine in spiked drinking water. At a concentration level of 2.0 × 10–1 moll–1 a recovery of 94 ± 6% was obtained, after tenfold concentration on Sep-Pak.  相似文献   

8.
Processes which occur in microwave discharges of dilute mixtures of SF6 and O2 in He have been examined using a flow reactor sampled by a mass spectrometer. Two classes of experiments were performed. In the first set of experiments, mixtures containing 6×1011 cm–3 SF6, 6×1016 cm–3 He, and O2 in the range (0–3.6)×1013 cm–3 were passed through a 20-W 2450-MHz microwave discharge. The gas mixtures arriving at a sample point downstream from the discharge were examined for SF6, SF4, SOF2, SOF4, SO2F2, SO2, F, and O. In the second class of experiments, rate coefficients were measured for the reactions of SF4 with O and O2 and for the reaction of SF with O. The rate coefficient for the reaction of SF with O was found to be (4.2±1.5)×10–11 cm–3 s–1. SF4 was found to react so slowly with both oxygen atoms and oxygen molecules that only upper limits could be placed on the rate coefficients for these reactions. These values were 2×10–14 cm3 s–1 and 5×10–15 cm3 s–1 for reactions with O and O2 respectively. The observed distribution of products from the discharged mixtures is discussed in terms of the measured rate coefficients.  相似文献   

9.
Drift mobility of electrons in copolymers containing pyrazolyl fragment in the main or side chain of the copolymer is studied experimentally using the time-of-flight method. The mobility is an exponential function of the applied electric field, and its values for the copolymers range from 5 × 10–7 to 2 × 10–5 cm2 V–1 s–1 at the field strength ranging from 5 × 104 to 1 × 106 V cm–1. Based on the measured mobilities and the molecule parameters, which were obtained by a PM3 quantum-chemical calculation, the role of copolymer fragments in the transport of charge carriers is discussed.  相似文献   

10.
A rapid and sensitive spectrophotometric method for the simultaneous determination of sodium dodecyl sulphate (SDS) and sodium linear-dodecylbenzenesulphonate (DBS) with 1-stearyl-4-(4-aminonaphthylazo)-pyridinium bromide (SAPB) is described using the difference at the maximum absorption wavelength of the SDS- and the DBS-ion associate. SDS and DBS have been determined independently by measuring their respective absorbances at the maximum absorption wavelength. The apparent molar absorptivities of the SDS- and the DBS-ion associate are 8.0×104 l mol–1 cm–1 at 445 nm and 4.5×104 l mol–1 cm–1 at 424 nm, respectively. The calibration graph for SDS is linear in the range from 0.1 to 1.0×10–6 mol/l in the presence of 1.2×10–6 mol/l DBS and for DBS from 0.8 to 2.0×10–6 mol/l in the presence of 8.0×10–7 mol/l SDS. The relative standard deviation (n=15) for 8.0×10–7 mol/l SDS is 3.4% and for 1.6×10–6 mol/l DBS 2.1%. The proposed method has been applied to the simulatenous determination of SDS and DBS in river water samples.  相似文献   

11.
12.
Reactions of both SF4 and SF5 with F have been studied at 295 K in a gas-flow reactor sampled by a mass spectrometer. The rate coefficient for the combination reaction of F with SF4 to produce SF5 was found to increase from (0.9 to 3.0)×10–12 cm3 s–1 when the helium bath gas number density was increased from (2 to 26)×1016 cm–3. The values obtained here are three orders of magnitude higher than a recent estimate of the high-pressure value based on the modelling of photochemical studies. The experimental results have been compared with RRKM and master equation calculations in which a simplified Gorin model has been used to determine the structure of the transition state. These calculations show that reasonable agreement can be obtained between the experimental data and the calculation if a small (2 KJ/mol) activation energy is assumed. The rate coefficient for the reaction between SF5 and F to produce SF6 was found to be independent of helium bath gas number density within the range given above. The value obtained for the rate coefficient was 9×10–12 cm3 s–1 with an uncertainty of a factor of 2. This value is close to that of 1×10–11 cm3 s–1 computed from the simplified Gorin model and to the value of 1.7×10–11 cm3 s–1 deduced from modelling of photochemical experiments.  相似文献   

13.
The solvent effect on the quenching of singlet oxygen by -phenyl-N-tert-butyl-nitrone /PBN/ has been investigated by laser flash photolysis technique registrating luminescence kinetics of1O2. The values of the rate constant /kq/ of the quenching were at 293 K: /9.0±0.4/×106, /4.4±0.3/×106 and /18.3±0.5/×106 M–1 s–1 in toluene, chloroform and acetonitrile, respectively. The rate constant for the chemical interaction between1O2 and PBN, was kr<1×105 M–1 s–1kq independently of the solvent. At temperatures between 223 and 293 K in toluene Eq=0.4±0.4 kJ mol–1.  相似文献   

14.
Hydrated electrons (e aq ) formed in water radiolysis react with ethyl propionate with a rate parameter of 7.5×107 mol–1 dm3 s–1. The electron adduct in acidic solutions immediately (<100 ns) dissociates, yielding CH3CH2C=0 radical. This process in alkaline solutions is slower, k=1.4×105 s–1. The hydroxyl radicals abstract H atoms in about 50% from the -position of propionate.  相似文献   

15.
Summary Halo-compounds of which the half-wave reduction potential is equal to or less negative than that of carbon tetrachloride, are reduced by tetrachloroferrate(II) anions. The bimolecular rate constants measured at 250 in isopropanol are 2 × 10–5 M–1 s–1 and 1 × 10–4 M–1 s–1 respectively for CCl4 and CCl3CO2Me.  相似文献   

16.
The desorption rate of surfactant ions from nylon particles was investigated at the concentrations below the critical micelle concentration by applying the stopped-flow method. A mixing cell of stopped-flow spectrophotometer was modified with platinum electrodes for electric conductivity detection. The change in electric conductivity with time in the desorption process was monitored by a memory-recorder system. The surfactants used were sodium decyl, sodium dodecyl, sodium tetradecyl, and sodium hexadecyl sulfates. The desorption rate was independent of the surfactant concentration and the rate constants were obtained by applying the first-order reaction scheme. The adsorption rate constants were estimated from the experimental desorption rate constants and equilibrium constants assuming the second-order kinetics. The desorption rate constants were determined to be 1–6 sec–1 and the adsorption rate constants to be 2–8×104 mol–1 dm3 sec–1; the former decreased and the latter increased with increasing number of carbon atoms in alkyl chain of the surfactants.  相似文献   

17.
Antioxidant properties of phenols with ortho- and para-adamantyl substituents are studied by microcalorimetry using cumene oxidation as a model reaction. The experimental rate constants for inhibition by adamantylphenols (k 7) are comparable to the corresponding values for sterically hindered phenols, and the stoichiometric inhibition coefficient is higher than the calculated one. Adamantylphenols with adamantyl and methyl or methylene bridge groups in the ortho positions with respect to the functional group exhibit the maximal activity. The inhibition rate constant takes a maximal value of k 7 = 3.3 × 104 l mol–1 s–1 for 2,4-di-(adamantyl-1)-6-methylphenol and a minimal value of k 7 = 1.4 × 103 l mol–1 s–1 for 2,4,6-triadamantylphenol. The difference in the rate constants is due to steric hindrances in the reaction of a peroxy radical with the functional group of a phenol surrounded by bulky adamantyl groups.  相似文献   

18.
Summary The kinetics and mechanism of ligand substitution reactions of tetraethylenepentamine nickel(II), Ni (Teren), and triethylenetetraamine nickel(II), Ni(Trien), with 4-(2-pyridylazo)resorcinol (parH2) have been studied spectrophotometrically at I=0.1 M (NaClO4) at 25°C. In both systems two distinct reaction steps are observed. The rapid first step follows the rate law d[Ni(Polyamine)(ParH2)]/dt=k1 [Ni(Polyamine)] [ParH2]. The formation of ternary complexes of Ni (Polyamine) with ParH2 has been investigated under second order equal concentration conditions. The values of second order rate constants for the Trien and Teren reactions are (2.1±0.2)×104 M–1s–1 and (7.8±0.6)×103 M–1s–1 respectively at pH=9.0, I=0.1 M and 25°C.The rate law for the second step may be written as d[Ni(Par)2]/dt=k2[Ni(Polyamine)(ParH2)]. Values of k2 for the Trien and Teren systems are (2.5±0.1)×10–4 s–1 and (4.76±0.3)×10–5 s–1 respectively.  相似文献   

19.
A gas-chromatographic procedure is proposed for the determination of O-isobutyl S-2-(N,N-diethylamino)ethyl methyl phosphonothioate (mixed ester) at the maximum permissible level for the working area air (5 × 10–6 mg/m3) and at the safe reference level of impact for the community air (5 × 10–8 mg/m3). The procedure is based on trapping the mixed ester from air by a chemisorbent. Next, the analyte is extracted by hexane; transformed to O-methyl-O-isobutyl methyl phosphonate by silver nitrate in methanol; and, in the case of the working area air, the methanol solution of the derivative is chromatographed. In the determination of the mixed ester in the community air, a solution of O-methyl-O-isobutyl methyl phosphonate (dialkyl methyl phosphonate) in methanol is passed through a column with an adsorbent and transferred to the chromatographic system with a thermal desorption system. The relative error of the determination of the mixed ester in the working area and community air is no more than 28 and 40 rel. %, respectively.  相似文献   

20.
Pulse radiolysis technique has been used to investigate the reaction of oxide radical ion (O.–) with 4,6-dihydroxy-2-methyl pyrimidine (DHMP), 2,4-dimethyl-6-hydroxy pyrimidine (DMHP), 5,6-dimethyl uracil (DMU) and 6-methyl uracil (MU) in strongly alkaline medium. The second-order rate constants for the reaction of O.– with these compounds are in the range 2-5 × 108 dm3 mol–1 s–1. The transient absorption spectra obtained with DHMP have two maxima at 290 and 370 nm and with DMHP have maxima at 310 and 470 nm. The transient spectrum from DMU is characterized by its absorption maxima at 310 and 520 nm and that of MU by its single maximum at 425 nm. The intermediate species were found to react with N,N,N,N-tetramethyl-p-phenylenediamine (TMPD) with high G(TMPD.+) values ranged between 3.9 × 10–7 molJ–1 and 4.8 × 10–7 molJ–1. These radicals undergo decay by second-order kinetics (2k/ = 1.0-1.7 × 106 s–1). The reaction of O.– with the selected pyrimidines is proposed to proceed through a hydrogen abstraction from the methyl group forming allyl type radicals. These are mainly oxidizing radicals and hence readily undergo electron transfer reactions with TMPD.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号