Some aspects of scaling factor calculations for quantum-mechanical molecular force fields

Stages of the scaling procedure for correcting molecular force fields obtained in rough quantum chemical calculations are discussed. The procedure includes selection of the number of scaling factors and their determination using experimental vibration frequencies of isotopomers and related molecules. It is stated that the difference in anharmonicity corrections for light molecules and their heavy analogs is to be taken into account along with possible errors in vibration frequency assignments of both isotopomers and more complex related molecules.     

Calculation of the franck-condon factors for the transitions of CS2 ions and comparison with related photodissociation spectra

On the basis of the approximation of harmonic oscillation between SC and S for the symmetric stretching vibration of the CS₂⁺ ions, the Franck-Condon factors for the transitions of CS⁺₂ ions have been calculated using the potential curves and wavefunctions of the harmonic oscillator. The calculation results have been used for comparison with the photodissociation spectra via the transition, and for estimating the validity of the rotation constants and the bond length of state given in the previous studies. The photodissociation mechanism via the transitions of CS⁺₂ ions has also been discussed.     

Epsilon efficiency

This paper considers the extension of -optimality for scalar problems to vector maximization problems, or efficiency problems, which havem objective functions defined on a set .It is shown that the natural extension of the scalar -optimality concepts [viz, given >0, given a solution setS, ifxS there exists an efficient solutiony with f(x)–f(y), and given an efficient solutiony, there exists anxS with f(x)–f(y)] do not hold for some methods used. Six concepts of -efficient sets are introduced and examined, to a very limited extent, in the context of five methods used for generating efficient points or near efficient points.In doing so, a distinction is drawn between methods in which the surrogate optimizations are carried out exactly, and those where terminal -optimal solutions are obtained.The author would like to thank the referees whose thoroughness was extremely helpful for the revised paper.     

Distribution of Electrical Field Energy for Conversion of Methane to C2 Hydrocarbons via Dissymmetrical Electric Field Enhanced Plasma

Direct conversion of methane into C2 hydrocarbons through alternating current electric field enhanced plasma was studied under room temperature, atmospheric pressure and low power conditions. The distribution of electrical field intensity and distribution of energy were calculated with software that was developed by us according to the charge simulation method. The results indicated that the energy of tip of electrode was 0.36 J/mm3 and it was higher than the methane dissociation energy (0.0553 J/mm3). The methane located at this area can be activated easily. The higher-energy particles produced by dissociation collided with molecules around them and initiated consecutive reactions between free radicals and molecules. The method was proved to be valided and could be taken as a basis for the electrical field study concerned.     

The statistical generation of SCS values and interaction factors for the13C NMR spectra of arenes

A new methodology which statistically determines substituent chemical shifts (SCS) and interaction factors of adjacent groups for use in the³C NMR spectroscopy of arenes is described. From a data base of 15,255 signals we have computed several hundred of thesestatistical SCS values (SSCS values), and interaction factors for many common pairs of groups. Some interaction factors for 1,2,3-substitution are also reported. When these SSCS values and interaction factors are used to predict the signal position they are found to give a correlation coefficient of predicted verses observed values of 0.994 with a standard deviation of 1.5 ppm.     

Uniform approximate Franck-Condon matrix elements for bound-continuum vibrational transitions

Franck-Condon matrix elements are calculated approximately for vibrational transitions of a diatomic molecule from a bound electronic potential curve to a purely repulsive curve. The bound states are approached by exactly normalized Miller-Good wavefunctions uniform in both turning points. For the continuum wavefunction a single turning point uniform Airy approximation is taken. The resulting Franck-Condon matrix element is approximately done in closed form with the help of a new canonical integral for a product of harmonic oscillator wavefunctions and Airy functions. The degree of agreement with a closed form exact result is qualitatively discussed for transitions from the ground state of a Morse curve to the continuum of a particular repulse exponential curve.Dedicated to Professor Hermann Hartmann on the occasion of his 65th birthday.     

Detection and quantitation of a bioactive compound in Vicia narbonensis L. seeds by capillary electrophoresis-mass spectrometry: a comparative study with UV detection

Capillary zone electrophoresis with mass spectrometry (CE-MS) and UV detection (CE-UV) was applied to the quantitative determination of gamma-glutamyl-S-ethenyl-cysteine (GEC), a bioactive and unstable compound present in Vicia narbonensis L. seeds. This compound is responsible for, among other negative effects, palatability reduction and grain toxicity. In order to carry out the quantitative analysis of GEC, different conditions (such as composition, concentration and pH of the background electrolyte, and type and time of extraction) were studied. Also, adequate conditions for electrospray-mass spectrometry of this bioactive compound were investigated. The best extraction conditions of GEC from V. narbonensis L. seeds flour were obtained using ethanol-water (70:30 v/v) for 45 min. The use of a 20 m ammonium hydrogen carbonate at pH 7 provided adequate analytical conditions compatible with the unstable nature of GEC as well as with the requirements of CE-UV and CE-MS analysis. A comparative study was carried out between the different figures of merit of CE-UV and CE-MS for quantitative purposes. Both techniques provided similar limit of detection and can be applied with confidence within the same linear dynamic range. However, reproducibility and speed of analysis were better using CE-UV. The developed methods were readily applied to quantify GEC in seeds of 21 genotypes of V. narbonensis L. A good agreement between CE-MS and CE-UV results was observed corroborating the usefulness of both approaches for quantitative purposes.     

Interlaboratory GC/MS response factor precision

A quality control procedure for Fused Silica Capillary Column Gas Chromatography/Mass Spectroscopy (FSCC GC/MS) was tested and shown to produce similar response factors at five Spectroscopy (FSCC GC/MS) was tested and shown to produce similar response factors at five laboratories. The average relative standard deviation (RSD) of interlaboratory response factors for fifty three compounds of environmental interest determined at each laboratory at nominal injected weights of 20, 100, and 200 ng was found to be 18.9% for four of the five laboratories which participated in this work. These data demonstrate that similar response factors can be attained in routine GC/MS measurements when adequate quality control is maintained.     

Gas chromatographic analysis of 1,4-naphthoquinones

Summary A gas chromatographic method is described for the analysis of 1,4-naphthoquinone derivatives in the mixtures of their isomers. The best results were obtained using 7.5% XE-60 on Chromosorb G at 180°. Quantitative determination was carried out with 1,4-naphthoquinone as the internal standard and using relative response factors or by means of the direct calibration method.     

Some observatons on the derivations of solvent polarity factors from gas-liquid partition coefficients

Summary The derivation by Snyder of polarity parameters from gas-liquid constants for 81 solvents has been re-examined. It is shown that the correction for the influence of the molecular size of the solvents and solutes by means of the Flory-Huggins entropy expression is more successful than the original correlation as carried out by Snyder. The correction for dispersive and/or entropic contributions to the free energy of transfer in the original treatment is found to be inadequate. However, the effect of various more refined treatments on the final polarity parameters P, x_e. x_d and x_n is probably small.