LCI Pariser-Parr-Pople calculations of π-electron systems in nitrogen-heterocyclic molecules. Correlation with spectral data

Limited configuration interaction Pariser-Parr-Pople calculations were performed for 19 nitrogen heterocyclic aromatic molecules. After optimizing the semiempirical parameters for six “test” molecules, calculations were performed for the remaining thirteen molecules. Strong correlations were made with experimentally observed ionization potentials, singlet-singlet transition energies, polarizations and oscillator strengths as well as ground state molecular geometries for cases where these observations have been made. These correlations indicate spectral features which should be carefully examined experimentally to determine the effect of nitrogen substitution in aromatic hydrocarbon molecules.     

Geometrical aberrations and physical characteristics of approximately focusing X-ray monochromators of Johann's type

A model is described for the computation of the diffracted intensity distribution on monochromating crystals in approximatively focusing monochromators of Johann's type. Numerical examples and graphs illustrate the influence of geometrical aberrations in some practical cases. Results of computations allow rules to be drawn up for the choice of parameters of these monochromators according to the requirements of the diffraction problem which is being solved.     

Graphical solution of chromatic and geometric focusing of X-ray diffraction lines

A nomograph and a transparent chart, serving for the rapid determination of the simultaneous chromatic and geometric focusing of X-ray diffraction lines, are described.     

Single-phonon contribution to the hopping conductivity of amorphous solids

The electronic d.c. hopping conductivity of amorphous materials is calculated exactly up to the second power of the coupling constant of electrons and acoustic phonons. Its temperature dependence is discussed.Ke Karlovu 3, Praha 2, Czechoslovakia.     

On peripheral pion-nucleon interactions at 7 GeV

It is shown by analyzing the ^–1-nucleon interactions at 7 GeV that it is possible to select events which could be described by the one-pion exchange model. Among the 169 stars with identified recoil proton which were examined, there are approximately 17 events corresponding to the scheme having a nucleon in the lower vertex only, while the maximum number of cases having a pion-nucleon system there is 84, For the second group the distribution of the mass of particles emitted in the lower vertex has its maximum in the region of the nucleon isobar mass (T=3/2). The distribution of mass of particles emitted in the upper vertex is not in contradiction with the production of and mesons. The values of the square of the transferred four-momentum are distributed predominantly in the region of small values in agreement with the Salzman model.The authors express their sincere thanks to E. Fenyves, K. Lanius and K. D. Tolstov for permission to use their experimental data and to J. Pernegr and V. imák for valuable discussions.     

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