Spectrochimica Acta最新文献

The infra-red spectra of dimethyl sulphide, selenide and telluride in the liquid and vapour phases and also the Raman spectra are reported. It has been possible to assign most of the observed bands to the fundamental modes of all three molecules. The spectra of dimethyl telluride suggest that it has similar symmetry properties to its lighter analogues. From consideration of the infra-red spectra of solid dimethyl sulphide and some of its co-ordination compounds it has been possible to clarify some of the earlier assignments.

Using Wilson's FG matrix technique, general valence force constants and Urey—Bradley force constants of As(CH₃)₃, AsCl₃ and AsBr₃, all molecules of the type XY₃, have been calculated from published Raman data and structural parameters.

It appears however that the molecule As(CH₃)₃ cannot be approached by the Urey—Bradley force field. So the comparative study of the bonding characteristics is limited to the general valence force field data.

Deviations from proportionality form the major source of error in X-ray fluorescent analysis. By careful preparation of the sample and equally careful operation of the spectrograph these deviations can be confined to inter-sample differences in total mass absorption. In order to eliminate or estimate these differences a variety of methods have been described; but none have found universal application. The method of a self-consistent mass absorption correction does not share the shortcomings of its predecessors. Without any pre-supposition regarding the over-all chemistry, an approximate composition of the unknown is first calculated by direct reference to a standard. Using this approximate composition the total mass absorption of the unknown is determined for each operational wavelength, and this information then used to make a more accurate estimate of the composition of the unknown. This more accurate estimate provides the means for determining a yet more accurate value for the total mass absorption at each wavelength. Thus, by an iterative process, a self-consistent chemical composition is obtained, and this value is then corrected for other deviations from proportionality by reference to a set of standards, using a quadratic regression relationship. Although this method has only been applied so far to whole rock analyses, its application could prove to be much more extensive, for the computer programme described is so constructed that, by a simple interchange of the matrix block and reference standards, analyses could be made within the entire range of the X-ray spectrum.

The fundamental vibrational frequencies of syndiotactic 1,2-polybutadiene have been calculated. Valence force constants obtained from saturated hydrocarbons and from methyl derivatives of ethylene can be very satisfactorily transferred to this molecule. Accidental degeneracies between in- and out-of-phase motions of the two chemical units in the identity period have been found for some normal mode and their importance for the interpretation of the spectra of vinyl polymers is discussed.

It is shown that the analytical absorption band at 669 cm⁻¹ can be certainly taken as a characteristic “tacticity band”.

General valence force constants of CH₃AsX₂ and (CH₃)₂AsX (with X  Cl, Br) have been derived from the experimental vibrational spectra and the molecular parameters, applying the FG matrix method of Wilson.

As the approximation of Venkateswarlu and Sundaram for molecules of the type ZXY₂ could not stand here, an adapted framework of F matrix elements is proposed. The group of physically acceptable force constants in this series of analogous XY₃ and ZXY₂ molecules is discussed.

This work describes an electronic theory, based on L.C.A.O., of the integrated intensities of localized vibrators in π-electron systems.

Using this theory, we have shown that the solvation of polycyclic aromatic nitriles (CCl₄) is partially inhibited by steric effects due to peri hydrogen atoms.

Spectral changes in the fluorescence of benzo(f)quinoline due to hydrogen bonding with different proton donors have been studied in cyclohexane at room temperature. The fluorescence is noticeably enhanced in intensity with a shift to longer wavelengths by hydrogen bonding with ethanol and benzyl alcohol, while it is strongly quenched by hydrogen bonding with phenol. Moreover, hydrogen-bonded benzo(f)quinoline with acetic acid or trichloroacetic acid is non-fluorescent, but protonated compounds with these acids emit fluorescence in a region longer in wavelength than that of the fluorescence of free benzo(f)quinoline. The equilibrium constants of hydrogen bond formation calculated from the changes in fluorescence intensity with addition of different proton donors are somewhat larger than those obtained from the changes in the absorption spectrum. The basicity of benzo(f)quinoline in the excited electronic state has been discussed with respect to the hydrogen bonding ability in the state.

The integrated intensities of the fundamental infra-red absorption bands of CH₂F₂, CH₂Cl₂ and CF₂Cl₂ have been measured using the pressure-broadening technique.

Experimental results are interpreted in terms of displacement polar tensors, which give the change of the dipole moment of the molecule due to a set of displacements of the nuclei. The components of these polar tensors have been calculated for the nuclei of C, H, F and Cl for each of the studied molecules. The results obtained show that the bond moments hypothesis, used by most authors in the interpretation of infra-red intensities, is only a rough approximation. Thus, we have found that a bond stretching gives rise to a dipole moment change not directed along the bond but strongly deflected towards the most polarizable atom of the molecule. Similar results have been obtained for the bond bendings.