Volume 32, Issue 8

In a heat conducting diatomic gas enclosed between parallel plates, the second rank tensor polarization of the rotational angular momenta is non-zero only near the plates. Therefore the gas is birefringent only in a boundary layer which is a few mean free paths thick. The birefringence is calculated with the help of a differential equation and a boundary condition for the tensor polarization. The difference in the index of refraction for light polarized parallel, respectively perpendicular to the temperature gradient is evaluated for the gases N 2 and CO with the information obtained from the field effects on viscosity and on thermal conductivity, and from thermomagnetic pressure difference measurements. The effect is estimated to be of measurable size.

Phonon transport in locally disturbed media is considered. The steady state solutions of the Peierls-Boltzmann type equations are studied. In particular, the flux-dependence of local excitations is investigated. It is proven that for a large class of scattering processes only two types of steady states are possible: a hysteresis type and a threshold one. 4 different types of factorization procedures are applied and it is shown that for these cases the steady states remain nearly unchanged. The stability conditions are reformulated in such a way that one can give a geometrical interpretation. The only stable solutions are nodes. The necessary modification of our model system to allow for limit cycles is indicated. Also, a more complicated situation, where the interaction Hamiltonian H I is a superposition of terms of different order, is investigated. The resulting steady state solution is again a hysteresis.

The system of coupled Boltzmann transport equations for electrons and phonons in a metal is considered in the absence of a magnetic field. Usually these equations are decoupled by “Bloch′s assumption”, that is the phonon gas is considered to stay in equilibrium with respect to the trans­ port equation for the electrons. It is shown that the coupled system of equations has finite solutions only if some other relaxation process than the electron-phonon interaction is present, for instance the phonon-phonon-interaction. With some simplifying assumptions the full system of equations is solved for high temperatures. The contributions of the phonon-drag to the thermoelectric transport coefficients are derived and discussed.

Measurements of the neutral helium line widths were made in a high pressure electric shock tube plasma of electron density ~ 1 X 10 17 cm -3 and temperature ~ 1.5 eV. The measured half-widths are in ~10% agreement with the calculated widths based on GBKO theory. Electron densities were independently determined using a He-Ne laser interferometer. A factor ~ 1.7 discrepancy between measured and calculated Stark widths (or electron densities) reported by Kusch and recently by Einfeld and Sauerbrey could not be confirmed.

On the basis of the Minkowski formulation, the total energy-momentum tensor of a system consisting of matter and electromagnetic fields is derived from the macroscopic theory. The analysis of this tensor shows that the electromagnetic fields supply the matter with momentum and energy. Consequently, the electromagnetic part and the material part overlap each other in the total energy-momentum tensor. Hence it is impossible to divide the total energy-momentum tensor into an electromagnetic tensor and a material tensor. In a closed system, in general, only the total energy-momentum tensor has physical significance and can be defined. Further, the generalized force which acts on the matter is obtained and interpreted clearly.

An exact pseudopotential theory is presented for atoms and molecules with arbitrary number of valence and core electrons and arbitrary number of nuclei. Using the variation method an equation is derived for the best many-valence-electron wave function which is orthogonalized to the core orbitals. Using this equation the exact equation is derived for the many-valence-electron pseudo-wavefunction which does not have to satisfy any orthogonality conditions. The Hamiltonian of the pseudopotential equation is of surprisingly simple structure and does not depend on the energy and/or on the wave function of the valence electrons. It is shown that the simple model Hamiltonian which is used in many pseudopotential calculations can be derived from the exact equation by two plausible approximations. The theory is elucidated on the example of atoms with two valence electrons.

Intense ion beams produced in magnetically insulated diodes become fast plasma jets in the drift tube. If a pinch discharge is made over these fast jets they can be magnetically compressed to very small diameters of less than 10 -2 cm. Such fast highly focused plasma beams may have important applications for the ignition of thermonuclear microexplosions.

A dielectric instability of a collection of charged fermions interacting via Coulomb forces and subjected to a random external field is pointed out. It is shown that, as a result of localization produced by the random potential, an RPA Coulomb field can generate a dielectric instability, both static or frequency dependent, resulting in a static or oscillating crystalline arrangement of the fermions. In simple metals, such as the alkali metals, this mechanism is shown to provide an explanation of the existence of the crystal lattice and of acoustic phonons.

The absorption coefficients of the statistical wings of the Cs principal series lines 6 2 S 1/2 - n 2 P 3/2 (6 ≦ n ≦ 10) and 6 2 S 1/2 - n 2 P 1/2 (6 ≦ n ≦ 9) perturbed by Xe have been measured quantitatively The results are compared with quasistatic line wings calculated from the interatomic Cs -Xe potentials of Baylis 1 and Pascale and Vandeplanque 2 . In the far wings of the higher lines of the series indications of many-body interaction were found. Furthermore the behaviour of the shift of all principal series lines up to the 23 rd member was investigated in the density region between 1.63 X 10 18 and 1.9 X 10 19 Xe atoms per cm -3 .

The partial structure factor for sulphur in liquid CS 2 at 20 °C has been computed by combining published x-ray and neutron diffraction results. Assuming that there are no correlations of molecular orientations, it is found that the main peak height of this sulphur-sulphur partial structure factor is smaller than that for carbon-carbon. This result is discussed in relation to the solid state structure and recent theoretical calculations.

The microwave spectrum of bromoacetylene has been investigated in the frequency range from 7 GHz to 35 GHz. From Stark effect measurements the dipole moment has been determined as μ = 0.23 + 0.01 D, and the restructure has been derived in four independent ways from twelve isotopic species: C - H = 1.0553 Å, C ≡ C = 1.2038 Å, C - Br = 1.7913 Å (internal consistency better than ± 0.0003 Å). Quadrupole coupling constants have been determined for eleven isotopic forms and are e q Q = 541.47 MHz and 648.00 MHz for HCCBr 81 and HCCBr 79 , respectively. Rotation spectra have also been observed for excited states of the three lowest normal modes and for several isotopic forms. For the Br 81 (Br 79 ) species the rotation-vibration coefficients are α 5 = -10.98 (-11.02) MHz, α 4 = -1.57 (- 1.61) MHz and α 3 = + 12.88 (+ 13.40) MHz. For the bending vibrations, ν 5 and ν 4 , l-type doubling constants are obtained as ql 5 = 4.14 (4.17) MHz and ql 4 = 2.6 MHz. Analysis of the Fermi resonance between the first excited state of ν 3 and the l = 0 component of the second excited state of ν 5 gives the mixing ratio of these two states as a/b = 1.45 (1.51) and the interaction energy as W 3,5 = 1.313 (1.181) δ 3,5 for the Br 81 (Br 79 ) species. With an approximate value of δ 3,5 ≌ 25 cm -1 , the cubic force constant is obtained as κ 3,55 ≌ 44 cm -1 . The results are discussed in relation to the molecular properties of other halogen acetylenes and halogen cyanides.

It is shown that intramolecular hydrogen bonding can give rise to very fast nonradiative desactivation of the S 1 -state of indigo dyes. In those derivatives, which lack the possibility of internal hydrogen bonds, hydrogen bonding to suitable solvent molecules can provide the channel for fast radiationless transitions. As a consequence, drastic effects on the S 1 -state lifetime are observed both as a function of solvent and/or temperature.

In order to interprete the electronic spectrum of xanthoporphinogene CNDO/S-calculations were carried out under consideration of 1360 single excited configurations.

The 1 H-NMR spin-lattice relaxation time and lineshape in solid 2-, 3-, and 4-methyl-piperidine, in 2-and N-methyl-piperazine, and in NN′-diinethyl-piperazine has been measured from low temperatures to the melting point. For all cases, the experimental data can be described by classical rotation of the methyl group. Activation energies governing this motion are between 9 and 14 kJ/mole. Second moments are reduced from about 25 G 2 to 17 G 2 . No further line-narrowing was observed.

The photoelectron (PE) spectra of 1,2-di-(2-pyridyl)-ethylene 1, 1-(2-pyridyl)-2-(3-pyridyl)- ethylene 2, 1-(2-pyridyl) -2- (4-pyridyl) -ethylene 3 and 1,2-di-(4-pyridyl)-ethylene 4 all in their trans conformation have been measured using He I radiation. For 1 - 4 standard SCF LCAO MO calculations were performed changing the angle of twist ϑ of the pyridine rings around their bonds to ethylene conrotatively from 0° to 60°. Comparison of PE spectra and these calculations allowed the assignment of all π-ionizations and indirectly also the nitrogen lone pair ionizations in 1 - 4 but not a determination of their conformation in the gas phase. There is only indication that ϑ in these molecules is rather small (ϑ<30°).

The microwave rotational spectrum of the most abundant species of 3-Cyanothiophene was investigated for the ground vibrational state. Rotational constants and centrifugal distortion constants are given. The electric dipole moment components μ a and μ b and the 14 N-quadrupole coupling constant X + = X bb + X cc were determined from the Stark-effect splittings and hfs-splittings respectively. The experimental results are compared to CNDO/2 calculations and are discussed with reference to ring distortion.

The radial Schrödinger wave equation with Morse potential function is solved for HF molecule. The resulting vibration-rotation eigenfunctions are then used to compute the matrix elements of (r - r e ) n . These are combined with the experimental values of the electric dipole matrix elements to calculate the dipole moment coefficients, M 1 and M 2 .

A simple way of determining the helix screw sense of a cholesteric phase using the Grandjean-Cano method is described. The helix pitch as well as its sense is investigated for ten cholesteric phases, induced by mesogenic chiral com­pounds in the nematic isomere mixture of 4-methoxy-4′-n-butylazoxybenzene (Nematic Phase 4, Merck). For the chiral compounds with nematic-like molecular structure it is found that the screw sense alternates with the number of bonds between the chiral centre and the ring system.