An analysis of the thermochemistry of the kinetic parameters of the elementary reactions involved in the pyrolysis of pentachloroethane has resolved several disputed, unclarified, or inconsistent aspects of the reaction mechanism. The resulting mechanisms for the inhibited and uninhibited pyrolysis account for all reported experimental findings. On the basis of this interpretation, first experimentally based values have been derived for the following: DH0(CCl3–CHCl2) = 79.0 ± 1.0 kcal/mol, ΔH(CHCl2) = 25.7 ± 1.0 kcal/mol, and E1 = 59.7 ± 1.0 kcal/mol C2HCl5 . 相似文献
In positron annihilation measurements it is often necessary to compare annihilation line shapes or angular distributions obtained
from a single sample subjected to different experimental conditions, or from a range of samples subjected to different mechanical
or metallurgical treatments. The difference of the normalised, distributions provides a convenient, easily visualised, and
comprehensive summary of the experimental results. Changes in the shape of these difference curves can be shown to arise only
when within the material under examination competition occurs between different types of positron trap. Some of the factors
affecting the shape of these difference curves are discussed in terms of trapping model concepts. By using the running integrals
of the difference curves (RID curves) a representation is obtained which is very little affected by the number of channels
spanning the line, provided that there are enough, leads naturally to an optimised determination of the line shape parameterS, leads to the definition of a number of parameters related to the shape of the difference curve and has well defined statistical
properties. Examples of RID curves show the range of shapes encountered, shape changes associated with competition between
different types of positron trap, and artefact shapes associated with rate dependent effects in the detector and electronics. 相似文献
Quantitative analysis of the brightener component bis (sodium-sulfopropyl) disulfide (SPS) in acidic copper plating baths poses a real challenge due to the complex chemical matrix containing large amounts of Cu(II) ion and sulfuric acid together with other organic additives and additive decomposition products. We developed a new ion-pair chromatography method to analyze micro-molar amounts of SPS directly in plating bath samples without the need for sample pre-treatment. Addition of tetra-N-methylammonium cation as ion-pairing agent to a methanol-sulfuric acid-water eluent increases the retention time of the anionic SPS2- on a C18 column sufficiently to separate this compound from Cu(II) ion and additive by-products. 相似文献
In this paper we motivate and describe an algorithm to solve the nonlinear programming problem. The method is based on an exact penalty function and possesses both global and superlinear convergence properties. We establish the global qualities here (the superlinear nature is proven in [7]). The numerical implementation techniques are briefly discussed and preliminary numerical results are given.This work is supported in part by NSERC Grant No. A8639 and the U.S. Dept. of Energy. 相似文献
A complex fine structure in the C? H stretching region of the infrared spectrum of deformed polyethylene single crystals is reported. The deformed crystals are shown to be transformed from the orthorhombic crystal form to a monoclinic structure. The previously deduced C2/m monoclinic structure does not account for the appearance of the new bands. An alternative but similar monoclinic structure is proposed. The symmetry of this structure is consistent with the Fermi resonance interactions required for the observation of these bands. 相似文献
Equilibrium constants for the reaction CH3COCH2CH3 + I2 ? CH3COCHICH3 + HI have been computed to fit the kinetics of the reaction of iodine atoms with methyl ethyl ketone. From a calculated value of S(CH3COCHICH3) = 93.9 ± 1.0 gibbs/mole and the experimental equilibrium constants, ΔH(CH3COCHICH3) is found to be ?38.2 ± 0.6 kcal/mole. The Δ(ΔH) value on substitution of a hydrogen atom by an iodine atom in the title compound is compared with that for isopropyl iodide. The relative instability of 2-iodo-3-butanone (3.4 kcal/mole) is presented as further evidence for intramolecular coulombic interaction between partial charges in polar molecules. The unimolecular decomposition of 2-iodo-3-butanone to methyl vinyl ketone and hydrogen iodide was also measured in the same system. This reaction is relatively slow compared to the formation of the above equilibrium. Rate constants for the reaction over the temperature range 281°–355°C fit the Arrhenius equation: where θ = 2.303RT kcal/mole. The stability of both the ground and transition states is discussed in comparing this activation energy with that reported for the unimolecular elimination of hydrogen iodide from other secondary iodides. The kinetics of the reaction of hydrogen iodide with methyl vinyl ketone were also measured. The addition of HI to the double bond is not rate controlling, but it may be shown that the rate of formation of 1-iodo-3-butanone is more rapid than that for 2-iodo-3-butanone. Both four- and six-center transition complexes and iodine atom-catalyzed addition are discussed in analyzing the relative rates. 相似文献
The kinetic isotope effect (KIE) for carbon and oxygen in the reaction CO + OH has been measured over a range of pressures of air and at 0.2 and 1.0 atm of oxygen, argon, and helium. The reaction was carried out with 21–86% conversion under static conditions, utilizing the photolysis of H2O2 as a source of OH radicals. The value of the KIE for carbon varies with pressure and the kind of ambient gas; for air the ratio of the reaction rates 12k/13k has the value 1.007 at 1.00 atm and decreases to 0.997 at 0.2 atm; for oxygen and argon over the same pressure range the values are 1.002–0.994 and 1.000–0.991, respectively. The value of the KIE for the CO oxygen atom is 16k/18k = 0.990 over the pressure range 0.2–1.0 atm and is independent of the kind of ambient gas. No exchange of the oxygen atoms in the activated complex, followed by decomposition to the starting molecules, was observed. From the mechanistic standpoint the normal KIE observed for carbon at the high pressure is attributed to the initial formation of the activated HOCO radical, whereas the inverse KIE observed at low pressures is a result of the KIE for the reverse reaction HOCO? → CO + OH being greater than that for the forward reaction HOCO? → CO2 + H. The derived isotopic equilibrium constant for HOCO ?CO favors the enrichment of 13C in the more strongly bound HOCO. 相似文献