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21.
Simple calculations can help to predict which derivatives in a series of organic compounds are potential lasing material. In conjugated systems, a necessary condition for lasing is that there is not less than a specific minimum energy difference between a first excited allowed and a second excited forbidden transition. This order of transition and energy spacing can be obtained by judicious substitutions even in molecules that do not meet these conditions. Lasing action in the near UV has been observed in five new compounds. 相似文献
22.
Treatment of indolines and N-acylindoles with HF/SbF5/CCl4 yields 6-trifluoro derivatives (indole numbering) whereas indoles and oxindoles give the 5-trifluoro derivatives in good yield. 相似文献
23.
Jean-Claude Yakoubsohn 《Numerical Algorithms》1995,9(2):223-244
We give a new theorem concerning the convergence of Newton's method to compute an approximate zero of a system of equations. In this result, the constanth
0=0.162434... appears, which plays a fundamental role in the localization of good initial points for the Newton iteration. We apply it to the determination of an appropriate discretization of the time interval in the classical homotopy method. 相似文献
24.
Jean-Claude Yakoubsohn 《Numerical Algorithms》1994,6(1):63-88
We give a practical version of the exclusion algorithm for localizing the zeros of an analytic function and in particular of a polynomial in a compact of . We extend the real exclusion algorithm to a Jordan curve and give a method which excludes discs without any zero. The result of this algorithm is a set of discs arbitrarily small which contains the zeros of the analytic function. 相似文献
25.
Feng Ji Paul W. Percival Jean-Claude Brodovitch Brenda Addison-Jones Stanislaw Wlodek 《Hyperfine Interactions》1994,87(1):853-858
Muonium adds to allyl chloride, CH2=CHCH2Cl, to form two radicals: MuCH2CHCH2Cl (main product) and CH2CHMuCH2Cl (minor product). Both radicals were fully characterized bySR andLCR. In the main product, the LCR lines due to the35Cl and37Cl nuclei were observed. Also, the temperature dependence of various hyperfine coupling constants (hfc) indicates that both Mu and Cl eclipse the unpaired electronp
2-orbital in the minimum energy conformation. For the fragment-CH2Cl, the presence of Mu in the-position is found to affect significantly the hfc of Cl in the-position; an internal rotational barrier of 12 kJ mol–1 was estimated using a simpleV
2 torsional potential. 相似文献
26.
Martina Schwager Emil Roduner Ivan D. Reid Paul W. Percival Jean-Claude Brodovitch Stanislaw Wlodek Robert F. Marzke 《Hyperfine Interactions》1994,87(1):859-864
SR spectra of the ethyl radical adsorbed on porous silica were observed in transverse and in longitudinal magnetic fields in the temperature range 190–298 K. The line widths reflect the dynamic partial averaging of the hyperfine anisotropy due to reorientation and surface diffusion. 相似文献
27.
Based on the similarity in properties of arsenate and phosphate, the colorimetric method using the molybdene blue complex was tested in order to determine low As(V) concentration in waters. The influence of complex formation time, daylight, temperature and competitive anions (silicate and sulphate) upon complex formation was determined. Optimal complex formation was reached in 1 h at 20±1 °C and was slightly favoured when developed in daylight. The formation rate declined with decreasing reaction temperature and no influence of any of the competitive anions tested (at concentrations usually found in natural waters of granitic areas) was noted. The detection limit of this method was 20 μg As(V) l−1. This simple, fast and sensitive arsenic determination method is suitable for field analysis, especially for waters containing low levels of phosphate and organic matter. Through arsenate determination, this colorimetric method allowed the arsenite oxidation efficiency of five common industrial oxidants to be compared. H2O2 and MnO2(s) were not considered as effective oxidants as a high excess was necessary to ensure As(III) oxidation. NaOCl and KMnO4 were promising oxidants as they allowed complete arsenite oxidation with a small excess for NaOCl or even less than the electron stoichiometric ratio in the case of KMnO4. FeCl3 was the most effective oxidant among the reagents tested here. 相似文献
28.
We present in this paper two new effects observed in the state of molecular iodine: a very high diamagnetic correction in the vibrational level υ′ = 62 and an important orientation of the optically excited molecules due to predissociation. Both effects can be interpreted by taking into consideration the perturbation of the B state by other electronic states. 相似文献
29.
Nlate S Nieto Y Blais JC Ruiz J Astruc D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(1):171-176
Phenol tri- and nonaallyl dendrons (3 and 7, respectively) were functionalized at the focal position to give the new triallyl dendrons 4 and 6 and the nonaallyl dendrons 11 and 13 that contain a iodoalkyl or a bromobenzyl termini. All these dendrons were used for the [FeCp]+-induced hexafunctionalization of hexamethylbenzene in [FeCp(eta6-C6Me6)][PF6] (1) under mild conditions in the presence of KOH. These reactions directly yielded the 18-allyl and 54-allyl dendrimers 9, 10, and 14 with a [FeCp(eta6-arene)]+ unit located at the dendrimer core. Cyclic voltammetry studies were recorded in THF and DMF with these metallodendrimers and compared with those of analogous dendrimers or complexes of smaller size that contain a [FeCp(eta6-arene)]+ unit at the core. The decreased rate of heterogeneous electron transfer when the dendritic size increases first disclosed by Diederich and Gross is confirmed. The variation of the redox potential of the Fe(II/I) redox system with increasing dendritic size is negligible even in a solvent of high dielectric constant such as DMF. This trend is attributed to fact that the involved "redox" orbital is buried on the metal center, well protected by the shell of alkyl chains (electron-reservoir nature), unlike in ferrocene. The chemical irreversibility increases in THF as the dendrimer size increases, due to more facile ligand substitution with THF at the 19-electron level when the chain bulk increases. 相似文献
30.
The fraction b.p. ≦ 84° (0.001 Torr) from Burley tobacco condensate was carefully investigated using fractional distillation and preparative column and gas liquid chromatography aided by GLC/MS coupling. Among the 193 compounds thus separated and characterized by their spectral data, 81 were newly identified tobacco constituents. Most of the compounds isolated in the course of this work display flavouring properties which make them highly suitable for improving the flavour and aroma of tobacco and tobacco smoke. 相似文献