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81.
The formation of negative hydrogen ions in a conventional hollow cathode discharge has been investigated. A mixture of Ne and H2 proved to be more advantageous compared to pure hydrogen. The study has been performed by solving the electron Boltzmann equation, coupled with a system of balance equations for neon and hydrogen neutral and charged particles. The vibrational distribution function of hydrogen has been calculated. Our calculations show unusually high population of vibrationally excited hydrogen molecules in a Ne–H2 mixture, which explains the high density of negative hydrogen ions under optimal conditions (total gas pressure of few Torr, hydrogen number mole fraction of 1–10% and discharge current of 10–100 mA). Line intensities originating from highly excited neon states vs. hydrogen pressure have been calculated and a comparison with existing experimental results has been made. 相似文献
82.
The use of the reverse atom transfer radical polymerization (RATRP) to end-functionalize poly(methyl methacrylate) (PMMA) with fullerenes, e.g. C60 and C70 was described in this paper. The Cl-terrninated PMMA was prepared via RATRP with designed molecular weight and narrow molecular weight distributions, and then directly used to react with fullerenes to produce C60(C70) terminated PMMA polymers in the presence of CuBr/Cu/bipy or FeCl2/bipy catalysts. The resultant polymers exhibit good solubility in some common organic solvents, e.g. THF, CHCl3 and toluene, and were well structurally characterized by a variety of physical techniques. 相似文献
83.
84.
G. Gousset M. Touzeau M. Vialle C. M. Ferreira 《Plasma Chemistry and Plasma Processing》1989,9(2):189-206
A simple kinetic model predicting the concentration of oxygen atoms, metastable singlet molecules O2(a
1) and negative ions O — in the positive column of a DC glow discharge is developed. The calculated O and O2(a
1) concentrations are compared to previously reported measurements for pressuresp=0.2–2 Torr and discharge currentsI=10–80 mA. The electron density calculated from the continuity equationj=n
e
e v
d agrees well with experiment. The rate coefficients for electron impact processes used in the balance equations of O, O2(a
1), and O– were taken from the literature as a function of the reduced electric fieldE/N forE/N=40–80 Td. A reasonable agreement is obtained between the model and the experiment with a set of 10 reactions for the production and destruction of the above-mentioned species 相似文献
85.
86.
E. T. Denisov 《Russian Chemical Bulletin》2004,53(8):1602-1608
The transition state of addition of free radicals and atoms to multiple bonds is considered as a result of intersecting of two parabolic potential curves. One of them characterizes the stretching vibration of the attacked multiple bond, and another curve characterizes the stretching vibration of the bond formed in the transition state. The force constant of the latter is calculated by an empirical equation that correlates the force constant with the bond dissociation energy. In the framework of this model, the thermally neutral activation energy (E
e0) and the elongation of the attacked and formed bonds (r
e) in the transition state were calculated from the experimental data (activation energy (E
e) and enthalpy of reaction (H
e)) for the addition of an H atom and methyl, alkoxyl, aminyl, triethylsilyl, and peroxyl radicals to the C=C bond and the addition of H and CH3 to the C=O and CC bonds. Analysis of the data obtained showed that E
e0 depends linearly on the |H
e| + Ee sum, i.e., Ee0/kJ mol–1 = 14.2 + 0.61 · (Ee – H
e), and the bond elongation in the transition state for addition of the most part of radicals to ethylene and acetylene vary within (0.65–0.87)·10–10 m. The factors affecting the activation energy of the radical addition reactions are discussed.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1542–August, 2004. 相似文献
87.
Summary In this paper, polymeric hollow fibers prepared from pH-stable polypropylene were used as columns for micellar electrokinetic
capillary chromatography (MECC). The electroosmotic flow (EOF) for polypropylene hollow fibers was evaluated in the pH range
of 5.0–12.0. With untreated polypropylene hollow fibers a stabilized but enhanced EOF was achieved when SDS was used in the
buffer, decreasing the separation window for uncharged substances in MECC to impractical levels. Uncharged acrylamide and
charged 2-acryloylamido-2-methylpropane sulfonic acid surface modifications were used to lower the strength of the EOF, increase
the separation window and prevent local overheating that could melt the column wall. 相似文献
88.
J. Al Andari A. M. Diamy J. C. Legrand R. I. Ben-Aim 《Plasma Chemistry and Plasma Processing》1993,13(1):103-116
Electron temperature and ion density are measured in an air microwave-induced plasma (2450 MHz) by means of a floating double probe. A 'cinetic scheme for ion formation and decay is set up, and a relationship between atomic oxygen and ion densities is obtained. From this relationship an order-of-magnitude of atomic oxygen concentration in the discharge is derived and compared with results obtained by optical actinometry in another work. 相似文献
89.
D-72 resin supported nickel-copper catalysts prepared by solvated metal atom impreg-nation (SMAI) were studied by magnetic measurements and X-ray photoelectron spectro-scopy (XPS). The Ni particles on the catalysts are very highly dispersed and displaysuperparamagnetic behaviour. Ni-Cu alloy clusters were found to be formed. The sur-face compositions are different from the bulk concentrations. In contrast with the surfaceenrichment in copper generally observed on conventional Ni-Cu catalysts, the surfaces ofthese catalysts are enriched in nickel. The nickel is in both zero and valent states, whilecopper is mainly in metallic state. Catalytic data show that the formation of Ni-Cu alloyclusters has a profound effect on the catalytic activities of the catalysts in the hydrogena-tion of furfural. The activity of the Ni:Cu ratio of one bimetallic catalysts is much higherthan that of the Ni or Cu monometallic catalyst. 相似文献
90.
According to the new method of preparing core-shell nanospheres developed by our group, by using two monomers, 2-hydroxypropyl
methacrylate(HPMA) and vinyl acetate(VAc), two kinds of core-shell nanospheres with poly(ɛ-caprolactone) (PCL) as the core
and crosslinked poly(2-hydroxypropyl methacrylate) (PHPMA) or poly(vinyl acetate) (PVAc) as the shell were successfully prepared
under similar conditions. After degrading the PCL cores of the two kinds of nanospheres by lipase, the corresponding crosslinked
poly(methyl acrylic acid) hollow spheres and crosslinked poly(vinyl alcohol) hollow spheres were obtained. Results indicate
that the new method we proposed for preparing core-shell polymeric nanospheres via in-situ polymerization can be generalized to a certain extent, and it is suitable for many systems provided the monomer used is soluble
in water, while its corresponding polymer is insoluble in water.
Translated from Chemical Journal of Chinese University, 2006, 27(9): 1762–1766 [译自: 高等学校化学学报] 相似文献