摘要:

For systems in which a chiral substrate and a different chiral metal chelate are forming a diastereomeric complex it is often not possible to determine the complex formation constant using chemical shift data only. It is shown that an unambigu - ous determination of complex formation constants is possible by combining data obtained from chemical shift measurements and self diffusion measurements.

ISSN:0038-7010    

DOI:10.1080/00387019208020696

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The stimulated Raman scattering gain coefficient has been calculated for the Q01(1) vibrational transition in H2at various pump laser wavelengths (126–1341 nm) in the density range of 5–100 amagats at room temperature (298K) as well as liquid nitrogen temperature (77K). Our calculations indicate that the Raman gain saturates at a density of about 70 amagats at a constant temperature in the range of 77–298K. The Raman gain is greater by a factor of ∼1.7 at 77K as compared to 298K at a constant density of H2. Such as Na, K, Cs, Pb, Bi and Ba, etc. The lightest molecule, i.e. H2 has the highest Raman shift (v=4155 cm−1) and gain as compared to other molecules used for the SRS processes. Theatomic vapors are also very attractive Raman media mainly because of their electronic energy levels, which are in close resonance with the pump laser wavelengths and thereby increasing the Raman gain at the Stokes wavelengths. Insome cases the conversion efficiency as high as 50% has been observed [17]. However, there are some drawbacks associated with these vapors. For example, itis difficult to achieve the high vapor pressures needed for the SRS processes to occur at relatively lower temperatures. At high Temperatures, dimer concentraation in these vapors increases almost exponentially thus decreases the conversion efficiencies at the Raman scattered wavelenghts. Because of these problems associated with the atomic vapors, most investigators have concentrated on uning the gaseous media; mainly H2, CH4, HD, and D2molecules to study the SRS-processes.

ISSN:0038-7010    

DOI:10.1080/00387019208020697

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Laser-induced fluorescence excitation spectra of the methoxy radical have been obtained under sufficiently high resolution in a supersonic jet expansion. The rotational structure associated with its origin band has been identified in the midst of strong overlapping rotational transitions due to the hydroxyl radical in the 31490–31700 cm−1spectral region. Rotationally-resolved A2A1- X2E spectra of the 000band of methoxy have been explicitly assigned using the nomenclature for prolate symmetric top transitions in doublet states.

ISSN:0038-7010    

DOI:10.1080/00387019208020698

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

This paper establishes a clear relation between the photocount distribution (PCD) of a low light level signal and its autocorrelation function (AC). The conclusion is that the evaluation of the AC from the measurement of the PCD is equivalent to that of the AC. Although the signal to noise ratio decreases when AC evaluation is obtained from PCD measurements, this technique allows AC values to be obtained more quickly and easily. Theoretical evaluation of the variances involved in these measurements and a simulation checking procedure are also described.

ISSN:0038-7010    

DOI:10.1080/00387019208020699

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Although it is a widely occuring substance (for ex:1,2) natural vanillin is produced on a commercial basis only fromvanilla planifolia, a tropical orchid. Vanillin is of great economic importance for La Réunion Island (Indian Ocean) which is one of the main producers of that substance. Vanillin is of interest not only in cookery but also in pure chemistry (it is used, for example, as a lignin model compound3, its reactivity has been studied4, and empirical spectrophotometric determination of vanillin concentration is currently used5,6, besides the development of selective electrodes7).

ISSN:0038-7010    

DOI:10.1080/00387019208020700

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The complexes between phenols and N-tBocsarcosine N',N'-dimethylamide, N-tBoc-sarcosylsarcosine N',N'-dimethylamide or polysarcosine are investigated in dichloromethane by FT-IR spectrometry. In the two first sarcosine derivatives, complex formation occurs at the urethane and at the amide carbonyl groups. The lengthening of the peptide chain from n=2 to n=40 exerts only a weak influence on the stability constants.

ISSN:0038-7010    

DOI:10.1080/00387019208020701

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Apparent activation energies for the atomization of cadmium, copper, iron and lead from aqueous solutions and APDC-MIBK organic extracts have been derived from experimental data. Both the activation energies and atomization temperatures have been substantially decreased for organic extracts in pyrolytically-coated graphite tubes. In tungsten-impregnated graphite tubes have been observed a delay of analyte peaks and thermal stabilization effect. There has been a levelling effect of the W-modified atomizer surface on the apparent activation energies in both solvents. Employing W-impregnated tubes, lower atomization temperatures and peak-area calibration in analyses of organic solvents and extracts has been recommended.

ISSN:0038-7010    

DOI:10.1080/00387019208020702

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The vibrations of pyramidal AB3type molecules with C3vsymmetry are analyzed in terms of Cartesian co-ordinates, and analytical expressions for the four normal mode frequencies are derived as functions of two stretching and two bending force constants. Optimized values of these force constants are obtained for a number of tri-hydride and tri-halide molecules by substitution of available spectroscopic and geometric data. The physical validity of the model is confirmed by comparing the calculated and observed frequencies of several isotopic species.

ISSN:0038-7010    

DOI:10.1080/00387019208020703

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Second derivative spectrophotometry has been used to determine canrenone (I), the main degredation product in spironolactone (II). Second derivative at 300 nm was found linearly related to concentration in the range of 0.2–1 mg% I has been determined in II down to concentration level of 0.2 mg%. The results were found reproducible with a relative standard deviation of 1.7%.

ISSN:0038-7010    

DOI:10.1080/00387019208020704

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The intermolecular stretching vibration of complexes between several Schiff bases and phenols is observed between 160 and 100 cm−1in cyclohexane. The intermolecular force constant calculated by the Lippincott-Schroeder function is intermediate between that calculated from the OH…N part of the molecule and that incorporating the whole masses of the interacting molecules. The far infrared spectrum of the 2,3,5,6-tetrachlorophenol complex where proton transfer takes place is also discussed.

ISSN:0038-7010    

DOI:10.1080/00387019208020705

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor