摘要:

AbstractThe alignment of lyotropic liquid crystals in a magnetic field has been studied by line shape analysis of the T1process and 2D2H double quantum filtered (DQF) NMR to investigate water dynamics and orientational feature in Cetyltrimethylammonium bromide (CTAB)/Sodium Salicylate (NaSal)/D2O liquid crystals. The same system but in powder form was also examined. In the ordered liquid‐crystalline phase, the single quantum line shapes showed splitting of doublets due to the residual quadrupolar interaction, while the double quantum spectra observed splitting patterns with damped oscillation. The modified cone model is invoked to describe the restricted motions of bound D2O molecules. Ten to thirteen bound water molecules are found to associate with each CTAB molecule and the correlation time of wobbling motion of the bound water is in the time scale of 10−8s. At 10°C, the motional correlation times of water in the powder sample have the same magnitude as those in the oriented sample. This study shows that the analysis of DQF relaxation spectra provides a more detailed source of motional information than the normally used measurem

ISSN:0009-4536    

DOI:10.1002/jccs.200100140

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractIn this paper, a theory of Coulomb explosion of molecules in intense laser fields based on the Auger effect will be presented. We first show how to calculate the rate of Auger process and then show that multiple ionization processes can be induced by the Auger effect alone or by the Auger effect followed by autoionization. For the case of molecules, multiple ionization is in general followed by dissociation.

ISSN:0009-4536    

DOI:10.1002/jccs.200100141

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractRoom temperature phosphorescence (RTP) of aromatic hydrocarbons has been investigated in deoxgenated SDS micelles and in the presence of a hydrophobic heavy‐atom containing species. No RTP was observed in spherical or sub‐rodlike micelles. In the presence of a heavy‐atom containing species, a tremendous increase in phosphorescence intensity was observed during the sphere‐to‐rod transition induced by the addition of a strong electrolyte. The increased microviscosity and the incorporation of more heavy atoms during the micellar elongation will lead to an increase in the rate of intersystem crossing and a decrease in the rates of nonradiative processes, favoring the observation of RTP. At high temperatures, the phosphorescence intensity is reduced dramatically probably because of the decrease in rigidity and aggregation number of the micelle with less heavy atoms incorporated. Various heavy‐atom containing species induce RTP to a different extent. Iodoethane exhibits the most prominent heavy atom effect. 1,2‐Dibromoethane, 1‐bromopropane, and bromobenzene are about 40% as efficient as iodoethane in inducing RTP, while long‐chain 1‐bromoalkanes and polar species are much less efficient. This study demonstrates the feasibility of detecting RTP in deoxygenated SDS rodlike micelles using a suitable hydrophobic heavy‐at

ISSN:0009-4536    

DOI:10.1002/jccs.200100142

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractBy using laser‐enhanced ionization (LEI) technique, we have studied atomization efficiencies of the alkalihalides in an acetylene/air flame. As an aqueous solution of the metal salt was nebulized into the burner head, a flame with a high temperature of about 2500 K may cause dissociation of the ionic bond to release the free metal atoms. The ratio of the number density of free metal atoms present in the flame to the total number density of the same metal element nebulized determines the atomization efficiency. In this work, binary salt solutions including LiX, NaX, and KX (X=Cl, Br, and I) were used; each was prepared at 5 ppm (μg/mL) metal concentration. The atomization efficiency of the metal element was measured, as the accompanied halogen species was varied. We found that the ratios of atomization efficiencies of the akalielement in different halide compounds were almost equal to one. Atomization efficiency determination is dominated by the metal atom, but weakly influenced by the binding halogen species. The observation may be interpreted satisfactorily by using the Sugden‐Bulewicz model. Based on this model, the metal atomization efficiency for different halide compounds depends on the number densities of the halogen atoms and the related dissociation constants. For the binary salt with a small concentration and a large dissociation constant, the atomization efficiency determination tends to be dominated by the metal atom a

ISSN:0009-4536    

DOI:10.1002/jccs.200100143

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe radical cat ions of styrene (π‐type), generated by photosensitized electron‐transfer of 1,4‐dicyanobenzene (DCB), using 2‐methyl‐2‐nitrosopropane (MNP) as spin trap ping agents and nucleophiles as the co‐reactant were investigated. The spin‐trapped nitroxide radicals were subjected to HPLC‐ESR and mass spectroscopic studies. Long‐range hfsc were obtained by resolution enhancement. Mass spectral fragmentation pat terns sup port the regioselective formation of the trapped nitroxides, which is derived from theanti‐Markovnikov addition of the methanol to the β‐position of t

ISSN:0009-4536    

DOI:10.1002/jccs.200100144

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractTwo new linear tri‐nickel(II) complexes with an infinite polymeric chain, [Ni3(μ3‐dpa)4(C4O4Me)](BF4)1and [Ni3(μ3‐dpa)4(N3)](PF6)2, [dpa−= di(α‐pyridyl)amido anion], have been synthesized and their structures were determined by X‐ray diffraction. Compound1crystallizes in the monoclinic system, space groupC2/c, witha= 19.9078(3),b= 13.2986(2),c= 37.6622(5) Å, β = 94.091(1)°, Z = 8. Compound2crystallizes in the monoclinic system, space group P 21/n, witha= 13.323(4),b= 23.217(3),c= 17.528(5) Å, β = 94.42(3)°, Z = 4. The two complexes are described as one‐dimensional systems with the (C4O4Me)−, 1, or N3−, 2, serving as a μ‐(1,3) bridged ligand at the two axial sites of each [Ni3(μ3‐dpa)4]2+fragment. The Ni‐Ni distances of 2.400(1) and 2.402(1) in1and 2.389(2), 2.385(2) in2are obviously shorter than those of 2.4325(7), 2.4356(7) in the monomeric complex [Ni3(μ3‐dpa)4(N3)2]3. The magnetic properties of complexes 2 and 3 were studied by susceptibility measurementsvstemperature. The χMvsT plots of both complexes show a strong antiferromagnetic behavior. The simulatedJ13values are −95 c

ISSN:0009-4536    

DOI:10.1002/jccs.200100145

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractA series of phosphine‐imine rhodium(I) complexes have been prepared and characterized by both spectroscopic and X‐ray single crystal analyses. Their activity on catalytic polymerization of phenylacetylene is investigated. The study of the solvent effect on polymerization shows that aqueous medium can in crease the productivity of poly

ISSN:0009-4536    

DOI:10.1002/jccs.200100146

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractReactions of silver(I) and copper(I) 1,1,1,5,5,5‐hexafluoroacetylacetonate (hfacac) with dienes1, 2and3resulted in some stable complexes. All of them showed an equal molar ratio of hfacac to diene per coordinated metal ion. The structure of Ag(hfacac)(1)(THF)6was solved by X‐ray diffraction analysis. The complex crystallized in the monoclinic space group P21/n with a = 6.342(3), b = 32.891(7), c = 11.680(2) Å, and z = 4. It was mononuclear with inclusion of a solvent molecule. Since the C2vsymmetry of3retained upon forming both silver(I) and Cu(I) complexes, a fast equilibrium of dissociation/recombination must have happened in the solutions. The changes of1H and13C NMR chemical shifts caused by coordination were meas

ISSN:0009-4536    

DOI:10.1002/jccs.200100147

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractA series of binary Nb/Ti ox ides was prepared by co‐precipitation. Their structure and physico‐chemical properties in term of surface area, surface acidity, bandgap energy and life time of the radiation‐excited electron‐hole pair were examined. These properties were correlated to their catalytic activities in photodegradation of oxygenated organic pollutants in water. The organic pollutants under investigation were phenol, cyclohexanol and tetrahydrofuran (THF). The lab‐made titanium oxide and those doped with a small amount of Nb (molar ratio of Nb/(Nb+Ti) less than 20%) showed higher activities in degradation of the organic pollutants. However, the mineralization efficiencies were different for the three oxygenated organic pollutants. Nearly complete mineralization to form CO2could be achieved in the degradation of phenol. For cyclohexanol, only ca. 50% selectivity of CO2was obtained over all the catalysts. Similar low efficiency in complete mineralization was observed in the degradation of THF, but higher selectivity (ca. 65–75%) of CO2could be obtained on the binary oxide with Nb content less than 4 molar %. In contrast, the binary Nb/Ti oxide with equal Nb and Ti molar content gave the poorest catalytic activity. The photocatalytic activity is generally correlated well to the life time of the radiation‐excited electron‐hole pairs. The contribution of surface acidity to the photocatalytic activity was only demonstrated on the niobia‐dominant oxide catalysts to ward THF. The photocatalytic activity was found to have no correlation with the crystal line structure, the bandgap energy, the surface area or the surface

ISSN:0009-4536    

DOI:10.1002/jccs.200100148

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractMatrix‐assisted laser desorption/ionization (MALDI) in combination with mass spectrometry proved to be a viable method for identifying additives in polyethylene ex tracts. The MALDI mass spectra of additives standards were found to be very simple consisting of [M+H]+and/or [M+Na]+pseudo molecular ions with little fragment ions. For real samples, which of ten contain more than one additive, the production of only one or two ions for each additive makes the tentative assignment much easier. Collision induced dissociation (CID) of the pseudomolecular ion is used to confirm the tentative assignment. The analysis of highmolecular weight additives, such as Chimassorb 944 and Tinuvin 622 indicated that MALDI was superior to other ionization techniques such as electrospray ionization (ESI), desorption chemical ionization (DCI) and fast atom bombardment (FAB) in the analysis of high molecular weight polymer additives. Sample preparation was found to be more critical than DCI in the analysis of real sample. The signals were interfered by the low molecule weight polyethylenemolecules, which were co‐extracted with the additives. This problem was partially overcome by using acetone in stead of methanol to precipitate the low molecular weight polyethylenemolecu

ISSN:0009-4536    

DOI:10.1002/jccs.200100149

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY