摘要:

A method using ion chromatography-atomic absorption system (IC-AA) with on-line preconcentration unit is developed for the speciation of chromium in aqueous samples. Both Cr(III) and Cr(VI) species are pre-treated with sodium salt of ethylenediaminetetraacetic acid (EDTA) in consecutive steps. The treated samples can then be injected into an on-line preconcentration unit followed by ion chromatographic separation with UV or selective flame AA detection. Both chromium species can be separated within 10 minutes, and the method is applicable for aqueous samples with ppm levels of chromium.

ISSN:0038-7010    

DOI:10.1080/00387019108020672

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Natural abundance17O NMR chemical shift data formeta- andpara-substitued α,α,α-trifluoromethoxybenzenes recorded in acetonitrile at 75° C are reported. The17O NMR signals for the trifluoromethoxy compounds are deshielded by greater than 65 ppm compared to analogous methoxy compounds. A quantitative relationship between17O NMR chemical shifts for the trifluoromethoxy and methoxy benzenes is reported.

ISSN:0038-7010    

DOI:10.1080/00387019108020673

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A graphical procedure is presented which allows a determination of the average alignment of the molecular axes in partially oriented, low-symmetry planar molecules from the results of linear dichroism and fluorescence polarization spectroscopy. When applied to benz[a]anthracene, the method makes it possible to extract information on the previously unknown origin of the second excited electronic state.

ISSN:0038-7010    

DOI:10.1080/00387019108020674

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The vibrations of planar A3B type molecules with D3hsymmetry are analysed, by treating these molecules as a special case of A2BC types with C2vsymmetry. Analytical expressions for the four normal mode frequencies are derived in terms of four force constants, and optimized values of the latter for the boron trihalides and sulphur trioxide are obtained and briefly discussed. Frequencies of various isotopic species are also calculated.

ISSN:0038-7010    

DOI:10.1080/00387019108020675

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A remote sensing method for estimating the temperature of hot gas is described. The method is based on the relation between the rotational quantum number J' corresponding spectral line of maximum intensity in the fine structure of rotation — vibration emission band of diatomic molecules and the temperature T. The advantages of the method are very easy, rapid and accurate. In this paper the condition using the method is discussed.

ISSN:0038-7010    

DOI:10.1080/00387019108020676

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Unlike the parent diacid, the dimethyl ester of (αR,α'R)-dimethylmeso-bilirubin-XIIIα exhibits only a weak bisignate circular dichroism (CD) spectrum in a wide variety of solvents. This implies a loss of conformation stabilization afforded (in the diacid) by intramolecular hydrogen bonding, and with it the loss of an allosteric effect that forces the parent acid into theP-helicity conformational enantiomer.

ISSN:0038-7010    

DOI:10.1080/00387019108020677

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A simple spring model for molecular vibrations, which uses Cartesian co-ordinates for both longitudinal and transverse displacements, is applied to centresymmetric linear pentatomic molecules such as carbon suboxide and carbon subsulphide. Analytical expressions for the four stretching and three bending mode frequencies are derived in terms of seven independent force constants. By substitution of Raman and infrared frequencies, values of these force constants are obtained and briefly discussed. Eigenvectors of the normal modes and eigenfrequencies of various isotopic species are also calculated.

ISSN:0038-7010    

DOI:10.1080/00387019108020678

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In the present investigation, a study of the electron impact mass spectrometry data is reported for seven compounds of a series of some 3-(4-chlorobenzyl)-5-benzylidene-imidazolidine-2, 4-diones and 3-(4-fluoro or chlorobenzyl)-5-benzylidene-thiazolidine-2, 4-diones previously synthesized.

ISSN:0038-7010    

DOI:10.1080/00387019108020679

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Vibrational spectra of 9-Fluorenone, 9-Fluorenone-18O and 9-Fluorenone-d8have been recorded in the solid state and solutions in the infrared and (4000–100 cm−1) and in the Raman (4000–50 cm−1). Differential infrared linear dichroic spectra have also been measured. The assignment of the vibrational bands is performed using the group vibrational concept, isotopic shifts and polarization features of the normal modes.

ISSN:0038-7010    

DOI:10.1080/00387019108020680

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Absolute transition probabilities and oscillator strengths for 28 lines belonging to Kr II spectrum were measured. The lines were obtained in a highly repetitive pulsed source where a capillar tube (3 mm internal diameter, 80 cm long) is crossed by a high current pulse (700 to 1600 A). Relative transitions probabilities are obtained after measurement of peak intensities and Stark line widths, using a simple relation. Absolute Aijvalues were determined by using experimental values of the lifetime of the level 5p4D7/2>.

ISSN:0038-7010    

DOI:10.1080/00387019108020681

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor