Volume 40, Issue 5

In the present work, the problem “hydrogen storage in metals” is treated with the aid of the so-called New Tamm-Dancoff (NTD) procedure. We employ this method in lowest approximation for the evaluation of the electronic energy difference eigenvalue between a metal crystal with and without hydrogen centre. As an example we use Magnesium with hexagonal structure. For this system we calculate the difference eigenvalue with dependence on the displacement of the nearest neighbours and next nearest neighbours of the hydrogen centre, respectively. Finally we calculate the radial electron density distribution in the environment of the proton.

In this work we consider the static perturbation of the hexagonal lattice of magnesium by one stored hydrogen atom. Equations are given to evaluate the equilibrium positions of the ions in the disturbed crystal. The effect of the hydrogen atom is described by a so-called Kanzaki force, an additional force in the ideal lattice. The force between two ions of the ideal lattice is assumed to obey the harmonic approximation. The force constants are calculated form an effective ion-ion potential. The static Green tensor, which is the inverse of the tensor of force constants, is calculated and with its aid the equations of lattice statics are transformed. The transformed equations are solved under the assumption of a Kanzaki force acting only upon the nearest and next-nearest neighbors of the hydrogen atom at a tetrahedral interstitial site. Finally we calculate the volume change Δ V and compare the result with the experimental value.

We present a derivation of the QCD scaling law on the basis of asymptotic freedom

Perturbation method, using the properties of SO (2,1) algebra is applied to get a simple analytical formula for energy eigenvalues of the exponential cosine screened Coulomb potential.

If the universe as a whole can be described as an ordered succession of discrete (Eigen-)states, the parameter of this order, a number t (t ∈ ℤ.) plays the role of a quantizised time. Then a particle (with mass m) as a substructure of the universe no longer follows a classical equation of motion with the moment p and the position x. The functional connection between these two quantities is rather a distribution. Especially there no longer exists the classical union of differential equation-initial conditions-path. The path is now only understandable as average, introducing a continuously running time. A central part for finding p̄ and x̄ as such averages, is played by the expectation values of these new quantities. Since the expectation values depend on all discrete points x(t) ( − ∞ ≦ t ≦ + ∞), we find sumrelations, which we can approximate by integrals. The integration extends over all d.x resp. dp-elements, which are loaded with the probability of their appearance. Following this procedure p and x become operators. If we postulate p̄ and p̄ to fulfil Newtons law, we find the ψ x and ψ p functions, constituting the resp. probability densities, to be governed by Shroedingers equation. The necessary existence of a quantum mechanics can thus be a reference to the existence of a noncontinuous time.

Recently the inverse mean field method (Imefim) has been shown to lead to a specific energy dependence of the real central nuclear part, V, of the optical model potential for nucleon-nucleus scattering. Proceeding from V towards the imaginary volume term of the potential, W υ , application of conservation laws yields a specific energy dependence for W υ . It compares favourably with heuristic potentials.

The variation of density ϱ with temperature of p-n-nonyloxy benzoic acid in its isotropic, nematic and smectic-C phases is presented. The density jumps and the computed thermal expansion coefficient maxima suggest the order of the N - S C and N - I transitions to be first order. The pressure dependence of the transition temperatures as computed from the Clausius- Clapeyron equation and the presence of pretransitional effects at the N - S C and N - I transitions in the nematic phase are discussed.

An ESR study of the liquid crystals N(p-n-pentyloxy benzylidene) p-n-alkylanilines [alkyl = methyl, 50.1; ethyl, 50.2; butyl, 50.4] has been carried out using a nitroxide radical as paramagnetic probe. The order parameters determined in this way are in close agreement with those determined from refractive indices by the Neugebauer method.

The density, refractive index and ultrasonic velocity dependence on temperature for N-(p-npentyloxybenzylidene)- p-n-octylaniline, 50.8, is presented. The compound 50.8 exhibits smectic-B, smectic-A and nematic phases between the solid and isotropic liquid phases. The nematic-isotropic and smectic A-smectic B phase transformations are found to be first order. The interesting smectic A - nematic transformation is confirmed from the results to be second order, although the thermal expansion coefficient and reported enthalpy data had suggested a weak first order transition. The computed adiabatic compressibility, β ad , molar sound velocity, R n , and molar compressibility A w are presented.

The v 2 fundamental band of cyanobutadiyne, HC 5 N, is accompanied by a number of strong hot bands arising from the low energy bending exicted states. We have assigned and analyzed the hot band from the ν 11 = 1, 2, and 3 states and the ν 10 = 1 state. The l-type doubling effect has been observed in the hot band of ν 11 = 1, while the hot band of ν 10 = 1 did not show the splitting. The diode laser spectra were recorded between 2250 and 2260 cm −1 .

Surface impurities on spherical Au and Cu crystals grown from a drop of melt on graphite in UHV were analyzed by Auger electron spectroscopy after the metals had been cleaned by melting resp. roasting in air. Crystals of Au-Cu alloys grown by the same technique show enrichment of the less abundant component. The well known reconstructions Au(001)(5×20) and Au(111)(23×1) could not be detected by RHEED and LEED on cleaned Au crystals. But both structures were confirmed on crystals of Au + 45 at ppm Cu. Au(110)(1×2) was present on cleaned and weakly Cu alloyed Au crystals.

A numerical investigation on the basis of a collisional-radiative (CR) model has shown that laser oscillation between the levels with the principal quantum numbers i = 2 and 3 can be generated in a recombining hydrogen plasma interacting with a dense helium gas as a cooling medium in TPD-I, which is a magnetically confined quiescent high-density plasma source consisting basically of two parts, namely, the discharge region with the cathode at the center of the cusped magnetic field and the plasma column region with the axial magnetic field. The population inversion is found to exceed significantly a threshold level for the laser oscillation even in the quasi-steady state when the hydrogen plasma with n e = 10 13 ~ 10 14 cm −3 interacts with the helium gas with a pressure of about 50 Torr.

The structure factors of molten LiNO 3 , RbNO 3 and AgNO 3 and the 1:1 LiNO 3 -RbNO 3 mixture have been determined over a wide range of momentum transfer by neutron total scattering measurements using a pulsed spallation neutron source. Least-squares analyses applied to the intra-ionic part of the structure factors have revealed the geometry of nitrate ions to be equilateral triangular (the D 3h symmetry) in the melts, independent of the cations involved. The radial distribution function (RDF) of the AgNO 3 melt has indicated that about four nitrate ions are bound to an Ag + ion as a monodentate ligand with the shortest Ag-O distance of 240 pm. The contact between lithium atoms and nitrate ions was also evidenced at about 190 pm in the RDF of the melts containing lithium ions, but the orientation of the nitrate toward lithium ions was not conclusive in the present study.

Fluorescence and phosphorescence spectra, fluorescence and phosphorescence quantum yields and phosphorescence lifetimes of the benzologues I -V of thiophene have been measured in ethanol at 77 K. By comparing the energies of the lowest triplet states of the molecules with those of corresponding hydrocarbons it is concluded that the sulphur atoms act like substituents and are not equivalent to aromatic double bonds. The rate of the radiationless deactivation of the lowest triplet state depends on the energy gap Δ E(T 1 - S 0 ) in accordance with the Siebrand relation. An unexpected small intraannullar heavy-atom effect of the sulphur is observed in 2,2′-bis-benzo[b]thienyl (II), a strongly fluorescing compound. As the most likely explanation it is concluded from experiments that in II the interaction between the heavy-atom and the π-MO’s of the hydrocarbon fragment (1,4-biphenylbutadiene) is much smaller compared to that in other structurally related benzologues of thiophene. External heavy-atom perturbers (AgClO 4 , CH 3 J) have a strong influence on the vibronic structure of the phosphorescence spectrum of IV.

By activation of the host lattices Sr 3 La 2 W 2 O 12 and Ca 2 La 0,5 Na 0,5 WO 6 with the trivalent rare earth ions Ln 3+ = Pr, Sm, Eu, Tb, Dy, Ho, Er a cathodoluminescence in the visible region is obtained. The influence of the electronic structure and concentration of the activator on the relative emission efficiency as well as the host lattice participation in the energy transfer processes are discussed.

The ground state rotational spectrum of propane has been investigated between 6.4 and 26.5 GHz with a microwave Fourier transform spectrometer and between 140 and 300 GHz with a millimeter-wave spectrometer. High J transitions have been measured and fitted to a centrifugally distorted Hamiltonian including some sextic coefficients. The results of the analysis are sufficiently accurate for the prediction of all strong transitions of astrophysical interest.

In vanadium-doped CsCl crystals grown from aqueous solutions anisotropic EPR spectra due to VO 2+ are observed and analyzed at room temperature. Evidence is presented that isotropic spectra of this ion observed in this and other compounds are due to inclusions of growth solution and not to rapid rotation of the vanadyl ion in the solid as normally assumed. At 77 K a well resolved vibrational progression of about 820 cm −1 is observed in the first ligand field band of this ion. The optical absorption spectra indicate the presence of a second valence state of vanadium, most likely V 3+ , in varying proportions depending on the crystal growth temperature.

Computer simulations of the dissociation dynamics of argon and xenon neutral and singly charged clusters with 5 - 20 atoms were performed. It is shown that the stability of clusters with ‘magic numbers’ of atoms (n = 19 for argon, and n = 13,19 for xenon) as found in TOF mass spectra, is more enhanced by ionization than that of their neighbours, indicating the importance of the ionization for the cluster size distribution found in experiments.

Molar volumes of molten CaCl 2 -NaCl, LaCl 3 -NaCl, LaCl 3 -CaCl 2 and the quasi-binary systems LaCl 3 -nNaCl · mCaCl 2 (mole ratio n : m = 1:3.2, 1:1, and 2.6:1) have been measured by the dilatometric method, and expressed as functions of both temperature and mole fraction by means of least squares regression. The molar volumes of molten LaCl 3 -NaCl and LaCl 3 -CaCl 2 showed positive and negative deviations, respectively, from additivity, while CaCl 2 -NaCl and the three quasi-binary systems satisfied approximately the additivity. The isotherm of molar volume for ternary LaCl 3 -CaCl 2 -NaCl system at 900 °C was represented according to the isotherms of three binary and three quasi-binary systems.

The trans → cis photoisomerization of a series of substituted stilbazolium salts (A t + X − , A t + : trans-1-alkyl-4-[4-R-styryl]-pyridinium and -quinolinium, R = CN. H, CH 3 and OCH 3 , X − = I and ClO 4 − ) was studied by laser flash photolysis and steady state irradiation measurements. The quantum yields of cis ⇄ trans photoisomerization (ϕ c → t and ϕ t → c ) and of fluorescence of the trans isomers (ϕ f ) were determined in several solvents at room temperature and at low temperatures in mixtures of either 2-methyltetrahydrofuran-dichloromethane or ethanolmethanol (E-M). In polar solvents at room temperature ϕ t → c is substantial ( ≧ 0.3) and ϕ f is small (10 −3 -10 −2 ). Competition of fluorescence and an activated step in the trans → cis pathway is indicated by the effects of temperature on ϕ f and ϕ t → c (activation energy: 2 - 3 kcal/mol). A transient, observed only at low temperatures (lifetime τ T > 0.5 ms in E-M below -170°C), is assigned to the lowest triplet state with trans configuration. On the basis of the effects of temperature on ϕ f , ϕ t → c , and the triplet yield and those of quenchers on ϕ f and ϕ t → c , involvement of the triplet state in the twisting process at room temperature is excluded. Therefore, a singlet mechanism is suggested for the trans → cis photoisomerization of the stilbazolium salts examined. Significant reduction of ϕ t → c for iodides in solvents of moderate polarity, where ion pairs are present, is accounted for by photoinduced electron transfer in competition to trans → cis photoisomerization.

Taking into account a “theorem of the addition of gravitational potential differences”, gravitational transformations turn out to be transitive.

The 4 s electron contact density was measured on 57 Fe atoms embedded in Au and in graphite. With the help of the isomer shifts measured on the same sources an estimate of the radial difference 〈Δ r 2 〉 was obtained which is rather independent of assumptions: - 〈Δ r 2 〉 < 9 x 10 −3 fm 2 at 80 per cent confidence.