Volume 38, Issue 4

A fast dissipation of a certain amount of energy at a solid surface by a mechanism whatsoever may cause a non-equilibrium phase transition of the surface material forming nearly instantaneously a relatively large amount of gaseous molecular and atomic ions. This is known to be a phenomenon common to many techniques utilized to create ions especially from organic solids. The thermodymanics of these processes are deduced from first principles; physical properties (kinetic energy and angular distributions, excitation energy) and chemical properties (ion types, mass spectra and intensities) are derived. Like “temperature” as an intensive quantity plays a major role in equilibrium thermodynamics, “action” as an extensive quantity takes the counterpart in this very far-from-equilibrium behaviour.

Neutron diffraction experiments were performed with five molten Bi-Zn-alloys and the two molten elements Bi and Zn. The total structure factors and the pair correlation functions are given. The concentration dependence of the experimental nearest neighbour distances and the experimental coordination numbers is in accordance with the segregation behaviour prevailing in these melts.

The unsteady propagation of shock waves in a dusty gas is investigated theoretically. The characteristic equations are obtained without neglecting the effect of the partial pressure of the particles. Numerical computations were carried out by Hartree's technique. As examples, the flow in a shock tube and in a blast wave is examined by applying a generalized piston problem. The results show that the existence of suspended particles may cause a rapid decay of the shock strength and that the flow field is devided into several regimes which are characterized by the shock position and the relaxation times.

Lattice-model calculations of the energies of surface director-configurations are presented. These configurations mediate between the homeotropic surface conditions and the bulk fingerprint texture of cholesteric layers. Their energy determines the asymptotic behaviour of the cholesteric-nematic threshold field in the limit of thick layers. The dependence of their energies on the elastic constant ratios could be brought into a simple scaling form. This form is in agreement with existing and newly presented measurements.

Ab initio studies of the spin density in mono- and bicyclic N hetero-aromatic compounds, and naphthalene are reported. The wave functions were constructed from both minimal and double zeta bases in all cases, and both RHF and UHF formalisms were used together with quartet annihilation. The statistical variations in correlations between spin population density and hyperfine coupling are investigated. After annihilation the MB and DZ wave functions become relatively similar, but do lead to some differences in assignment for the smaller values of a H . In general the agreement a H /a N between and calculated density is improved by two term rather than one term expressions, but there are still a number of experimental hyperfine couplings awaited.

A new matrix, 1,1,1-trifluorotrichloroethane, CF 3 CCl 3 , has been employed in radiation chemistry studies to stabilise positive ions. As a test, positive ions of benzene, toluene, orto-, meta- and paraxylene and biphenyl have been generated by y-irradiation of the solutes contained in the CF 3 CCl 3 matrix at 77 K. The ions have been investigated by ESR, and hyperfine couplings have been obtained. The data complement and correct the splitting values obtained previously in the adsorbed state.

Proton NMR investigations of the smectic-C phases of three 4,4′-bis-n-alkyloxy-azoxybenzenes (C 7 , C 8 , C 9 ) with temperature independent tilt angles are presented. The behaviour of well-aligned samples (strong magnetic field ≳ 1.5 T, slow cooling rate) under rotation in the field can be described by the models of Luz and Meiboom, and Wise, Smith, and Doane, (LM/WSD), resp. However, on polarization of the samples in presence of magnetic fields ≲ 0.75 T the molecular directors are not arranged preferentially parallel to the direction of the polarizing magnetic field but are rather inclined, i.e., the layers are stacked preferentially perpendicular to the original magnetic field direction (PSL model). It is shown that all the angular dependences of NMR second moments can be interpreted in terms of a superposition of the LM/WSD and PSL models, or, on the other hand, by assuming totally disordered fractions of the samples together with portions that fully obey the behaviour demanded by one of the above models (LM/WSD or PSL). The tilt angles derived from the comparison of experimental and theoretical angular dependences of the second moments for well-aligned samples are applied to the explanation of the experiments at lower polarizing fields successfully, too.

The rotational spectrum of ethyl acetylene has been investigated between 70 and 320 GHz. A Coriolis interaction has been found between the first excited state of the methyl torsion and the C - C = C in plane deformation. Splittings of transitions in the first excited torsional state show that the barrier hindering internal rotation of the methyl group amounts to 3271 cal/mole.

We present a new three and four level double resonance spectroscopy in the microwave region. A pulsed pump radiation and Fourier transform technique for detection of the signal radiation is used. This method is complementary to that using continuous microwave pump radiation.

Measurements of the Knight shift K H and the magnetic susceptibility of TaH 0.61 on thin foils, prepared from TaH 0.61 powder at high pressure, are reported. It is shown that the method leads to useful results and is applicable to brittle materials for which compact samples are not available. Both, K H and Χ y , are given for the hydrides TaH x in the range 0 ≦ x ≦ 0.74.

Semilocal pseudopotentials are used in combination with a density-functional approximation for the correlation energy and special optimized basis sets to investigate the sulphur halides SF, SF 2 , SF 3 , FSSF, SSF 2 , SCl, SCl 2 , ClSSCl and SSCl 2 . It turns out that the inclusion of d-orbitals in the basis set playes a significant role with respect to the quality of the calculated molecular parameters. Properties of SF 3 are calculated for the first time, and the differences between the disulphur difluorides and the disulphur dichlorides are explained.

It is shown that accurate upper and lower bounds to the eigenvalues of anharmonic oscillators can be obtained by means of the Rayleigh-Ritz variational method and two trigonometric basis sets of functions which satisfy Dirichlet and Von Neumann boundary conditions. Numerical results show that the Dirichlet basis set is more appropriate than the harmonic oscillator one for calculating eigenvalues and the value of eigenfunctions at the origin.

The interactions of Ni and Cu atoms with CH 3 OH and H 2 CO ligands were studied by means of ab initio MO calculations. The metal atom-ligand bond length is shorter for Ni than for Cu. Correspondingly, the binding energy is larger for Ni than for Cu. The difference in adsorptive properties of Ni and Cu is explained by the difference in their electronic structures. Alloying effects are discussed. The interaction of the Cu atom with the CH 3 O radical is also calculated.

BrO 2 was found as an intermediate in the reaction of bromate with alcohols (e.g. methanol, isopropanol, allylalcohol) or ketones (e.g. acetone). This reaction may be important for the understanding of bromate driven oscillators.

A detailed bifurcation analysis of the reaction-diffusion equations representing the trimolecular model of Prigogine and Lefever (“Brusselator”) is performed. The model considers also the diffusion of the initial component. The homogeneous solution to the problem cannot exist and the bifurcation analysis must be performed numerically. There are two ways of possible branching, either the basic branch will be followed or branching from an isolated branch may occur. In both cases, the branching is of the type symmetric → asymmetric → symmetric, etc. For higher dimension of the system a topologically interesting isolated branch of asymmetric solutions was discovered.