Volume 35, Issue 4

Seven polycrystalline iron meteorites (Forsyth County, Holland's Store, Wathena, Pima Co., Chico Mountains, Kopjes Vlei and Mejillones), of bulk composition as normal hexahedrites of group II A, are shown to be severely altered hexahedrites. Mic-roprobe examination and various heat treatments of synthetic alloys support the conclusion that the meteorites after a primary slow cooling were subjected to shock-reheating above 800°C. Thereby the following transformations took place a-α-γ->α 2 ->α, and an unequilibrated structure, very sensitive to grain-boundary corrosion was formed.

In an atomic beam of Lu, six levels of the configuration 5d 6s 6p in the energy range 18000 to 23000 cm -1 were selectively populated with the light of a pulsed dye laser. Time resolved observation of the recmitted resonance light was used to deduce the lifetimes of the excited levels.

By considering three successive approximations to the conduction-electron wavefunction of metallic lithium, it is shown that the X-ray scattering factor at small wavevectors is very sensitive to the model chosen for describing the electron density. It is demonstrated that, when screened pseudopotentials are used, the "solid state effect" is almost negligible in this region of wave-vectors.

The spectral characteristics (absorption, fluorescence and lifetimes of fluorescence) of methine dyes in different solvents are presented. The results show that the methine dyes in polar solvents emit a dual fluorescence. From the dependence of the fluorescence spectrum on the dye con-centration it is suggested that excimer formation is responsible for the second band of fluorescence.

The coulometric titration technique is extended to treat general cases of systems of any number of components. Complete equilibrium phase diagrams and thermodynamic properties are obtained from readily and precisely measurable electrical quantities, employing only a small number of samples. General equations are derived which directly relate the cell voltage to the standard Gibbs energies, enthalpies and entropies of formation of all phases involved without the necessity of considering specific cell reactions. The application of the technique to the ternary system Cu-Ge-O is demonstrated.

Raman-and IR-spectra of four compounds of the general composition Tl 6 I 6 M 2/n n+ (I 4 ) [n: formal valence of the M-atom, M = Ag, Au, Pb and (Bi 0.5 Tl 0.5 )] were investigated in order to identify the polyiodide species present. In accordance with structural results comparable amounts of I 4 2- and I 3 - /I - -groups were found for M = Ag, Pb and (Bi 0.5 Tl 0.5 ), while in Tl 6 I 6 Au 2 (I 4 ) I 3 - /I - -groups predominate.

The magnetic behaviour of CS 2 MHoF 6 (M = Na, K, Rb) has been studied in the temperature range between 3.2 and 251.3 K. The magnetic data are interpreted by means of a previously developed model in which the influence of the crystal field is theoretically described by the angular overlap model. Values of the angular overlap parameters e σ (R) and eπ(R) cannot be determined unequivocally. The energy values of the crystal-field levels of the 5 I 8 ground state are calculated.

A natural orbital multiconfigurational SCF formalism has been applied to the closed shell Hartree theory with orthonormal orbitals. A prescription is given for constructing a single, one-electron Hamiltonian with which one can determine all the occupied orbitals. The formalism is suited to the matrix formulation of the orthogonalized Hartree theory for polyatomic systems.

The optimised cluster theory of Andersen and Chandler has been applied to calculate the radial distribution functions of a triangular well fluid with the width a the hard sphere diameter The results agree well with Monte Carlo Calculations of Card and Walkley.

The dipole moment of the doubly deuterated species (CH 2 =CH-CH 2 -ND 2 ) of N-cis Lone-electron-pair isomer of allylamine has been measured. The "isotope pulling elfect" has been used to determine the relative orientation of the total dipole moment with respect to the principal axes in the normal species. The possible effects of large amplitude motions on the observed effective dipole moments are discussed.

CNDO/2 calculations have been carried out on a series of haloalkane-aromatic 1: 1 complexes in the ground and first excited singlet states and one 2 : 1 complex in the ground state. Calculated stabilities agree very well with reported experimental results for the ground state. Our calculations indicate that the substituent effect on complex stability in excited states will be the opposite of that found for the ground state.

The tracer diffusion coefficients of 86 Rb and 137 Cs ions in the molten (Li-Na)NO 3 , (Li-K)NO 3 , (Li-Rb)NO 3 , and (Li-Cs)NO 3 systems have been measured by means of a paper strip method. Results from the paper strip method in some pure nitrates are compared with the results from capillary and optical interferometric methods. With increasing concentration of LiNO 3 , the diffusion coefficients at 350°C are found to decrease in the (Li-Na)NO 3 system and to increase in the (Li-K)NO 3 , (Li-Rb)NO 3 , and (Li-Cs)NO 3 systems. For 86 Rb in (Li-K)NO 3 an increase is followed by a decrease. These findings are discussed by taking into consideration the free space in the solvent system and the ionic interaction between the diffusing and the surrounding ions.

Attempts to Calculate the Fluorescence Spectra of Organic dyes Within the scope of the PPP-approximation a β-variation procedure is used to calculate the fluorescence spectra of some organic dyes and to estimate geometry changes upon excitation into the fluorescent state.

The molecular structure of ethylbenzene has been studied by gas electron diffraction. Experi-mental intensities and radial distribution are well reproduced by an average structure with r = 70(3)°, where r is the angle between the C—C—C(H3) plane and the ring plane, mean (rg) bond lengths (C-C)phenyi = 139.9(3) pm, Cphenyi-C(H2) = 152.4(9) pm, C(H2)-C(H3) = 153.5(12) pm, C—H = 109.4(4) pm, and bond angle C-C-C(HS) = 111.8(15)°. (Estimated total errors are parenthesized.) An also acceptable perpendicular model (r = 90°) is accompanied by very large vibrational amplitudes, while the coplanar conformation (r = 0°) is excluded. Mixtures of conformers fit the experimental data as well. The barrier to rotation of the phenyl group is estimated from the average structure to be about 7 kJ mol -1 . According to CNDO/2 calculations, only the perpendicular form is stable. The results of a geometry optimization are shown.

Necessary and sufficient conditions for commutativity of two projections in Hilbert space are given through properties of so-called conditional connectives which are derived from the conditional probability operator PQP. This approach unifies most of the known proofs, provides a few new criteria, and permits certain suggestive interpretations for compound properties of quantum-mechanical systems.

The rotational spectra of the first excited state of the methyl torsion and the CCI-in plane deformation of CH 3 CH 2 I have been studied. A Coriolis interaction between these two modes has been found. Splittings of transitions in the first excited torsional state show that the barrier hindering internal rotation of the methyl group is 3.62 kcal/mole. This value agrees quite well with the value previously reported from Raman studies. It is internally consistent and similar to the other ethyl halides.

In aqueous BeF 2 -solutions of different concentrations and therefore different viscosities the magnetic relaxation time T 1 was measured as a function of the viscosity over a wide range by pulsed NMR-technique. For small viscosities a linear dependence of T 1 on the viscosity was observed as predicted by theoretical calculations. Since the ground state spin of 19 F is I = 1/2, the quadrupole moment vanishes. For observing quadrupole relaxation of the F-nuclei, one has to use an excited level. With the time differential perturbed angular distribution method (TDPAD) we observed the quadrupole relaxation time T Rel of 19 F in aqueous BeF 2 -solutions.

Three graphic polynomials of annulenes and radialenes are examined, namely the matching polynomial, the characteristic polynomial of the Hückel graph and the characteristic polynomial of the Möbius graph. Several relations between them are obtained. These six polynomials and their zeros are mutually closely related.

The effect of cycles on the HOMO-LUMO separation of alternant conjugated hydrocarbons is examined. A general topological regularity is established, namely that (4m + 2)- membered conjugated circuits increase and (4w)-membered conjugated circuits decrease the HOMO-LUMO separation. Möbius cyclcs exhibit an opposite effect.

A beam of electromagnetic radiation can generate magnetic fields in plasmas. It is shown that those fields grow significantly when the incident radiation is sufficiently strong. We obtain expressions for the characteristic time of the growth of the fields as well as for their spatial distribution and point out a possible mechanism, which can lead to the formation of a quasi-stationary state. The maximum value of the magnetic field strength is estimated

The fundamental definitions of the Total Energy and of the Vibrational Total Energy Distributions are presented in details in terms of either symmetry coordinates, or generalised symmetry forces, or generalized symmetry coordinates. This, give now a uniform tool for physicists and chemists in the field of characterisation of the normal vibrational modes of polyatomic molecules.

The emission anisotropics (r) of the fluorescence of the prolate molecules (whose emission transition moments are parallel to the long axis) 4-dimethylamino-4'-cyanostilbene, 4-methoxy-4'-nitrostilbene, 4-dimethylamino-4'-diphenylphosphinoxidstilbene, 4-dimethylamino-4'-bromstilbene and pbis[ 2- (5-α-naphthyloxazolyl) ] -benzene in solvents of different viscosities {η) have been studied. Also for these substances the non-linear dependence of 1/r on T/η was confirmed. This non-linearity in the low viscosity range can be explained by the assumption that the prolate luminescent molecules perform irregular rotational motions within a solid angle smaller than 90°. Effective volumes and rotational relaxation times for the different molecules in the different solvents were obtained.

The Raman band shapes of ν 1 of CDCl 3 and CH 3 I in the pure liquids and their mixtures are studied. The CH 3 I mode shows a broadening in the mixtures with a maximum at a mole fraction of about 0.5, whereas the ν 1 band of CDCl 3 , shows a splitting in the mixture. The different behaviour of the two Raman bands is discussed briefly.