Volume 28, Issue 9

The correlation function of the tensor polarization relevant for the depolarized Rayleigh line of a gas of rotating linear molecules is calculated for the pressure broadening regime. Point of depar­ture is the Waldmann-Snider equation for the distribution function of the gas. Due to the collisional coupling between the tensor polarization and other moments of the distribution function the cor­relation function turns out to be a sum of exponential functions. Consequently the depolarized Rayleigh line has a non-Lorentzian shape.

The Dirac equation is solved for mixed vector-scalar potentials. The limits on the scalar coupling constant are set by precision atomic experiments, We obtain the maximal size of the scalar coupling constant α' = 2.5·10 -8 per charge unit. Deviations from the Mott scattering are also determined.

Detailed studies have been made of the number densities of the neutral constituents of the negative glow of a hollow cathode discharge (with currents up to 120 mA) produced in N 2 at various pressures (0.2 <C p 0 < 2.0 Torr). The dissociation degree X N of N 2 in the presence of the discharge was determined as a function of gas pressure p 0 and discharge current I d and from these data an empirical expression was derived X N p 0 = C I d , with C = 7.6·10 14 particles cm -3 · A -1 . Using this result a value of the density [e s ] of the fast electrons present in the negative glow as a function of discharge current was calculated to [e s ] = 5.9·10 7 I d . Also an estimated reaction rate constant was obtained for the fast bimolecular process N + NO→N 2 +0 (3.3·10 -11 cm 3 s -1 ). Relative ionization efficiency curves at mass 28 and mass 14 in the presence and absence of the discharge yielded values of the ionization and appearance potential for N2+e→N 2 + +2e (15.55 ± 0.1 eV), N2+e→N + +N+2e (23.65±0.2 eV) and N+e→N + +2e (14.35 ± 0.4 eV).

IF was produced by microwave discharge of l 2 and C 6 F 10 (CF a ) 2 . The rotational transitions J=0→1 and 1→2 in the vibrational states ν = 0, 1, 2 were observed. The analysis of the hyperfine structure yields the following hfs constants: 127 I: e q v Q = (-3440.89+5.47 (ν+½) ±0.20) MHz, c I = ( + 90 ±10) kHz.

The first order perturbation expressions for various molecular constants such as isotopic shifts (⊿λ i , ⊿λ i /λ i ), inverse isotopic shifts (⊿σ i , ⊿σ i /σ i ), Coriolis coupling constants (Δξ ij )and mean amplitudes of vibration (Δ∑ ij ) obtained using different equations and approximations are given in detail. The mathematical and physical properties of the different approximations are discussed extensively. Incidentally some isotopic rules obtained using the first order perturbation theory are presented.

The validity of the Hamiltonian usually used for the analysis of the torsional fine structure in rotational spectra of two-top molecules with the invariance group C 3v - ⊗C 3v + has been checked. The numerical treatment of the Hamiltonian matrix by Van Vleck transformation gives nearly the same result as the direct diagonalisation used in this work. For each torsional state a different set of rotational constants should be used to reproduce the torsional multiplet splittings. The spacing between the multiplets is not given. This fact, illustrated by dimethylsilane (CH 3 ) 2 SiH 2 as an example, demonstrates the limitation in the validity of the Hamiltonian.

Particle densities of helium atoms in the ground and excited states have been calculated for non-L.T.E. plasmas on the basis of a collisional-radiative model in which singlet and triplet states have separately been taken into account. Distinction is made between two physical situations: 1- a homogeneous stationary state, 2- a transient and/or inhomogeneous plasma state. In both cases, the particle densities have been calculated for an optically thin, a slightly optically thick and strongly absorbing plasmas. Only the results for the homogeneous stationary state are presented in this paper. Those for the transient and/or inhomogeneous states have been summarized in numerical tables which will be sent on request. (Title: "Tables of reduced population coefficients for the levels of atomic helium", Report EUR-CEA-FC-697.) The tables are sufficiently complete to permit a wide application in the field of spectroscopic diagnostics of different types of non-L.T.E. plasmas. - Comparison of our results with the values measured by Boersch et al. 10 shows good agreement with our calculations when one assumes that the observed plasma is strongly inhomogeneous and dominated by diffusion.

The transmission coefficient of a plane electromagnetic wave into a cold, inhomogeneous, mag­netized, deuterium plasma half-space and its eventual absorption at the lower-hybrid layer is com­puted numerically for a wide range of parameters. It is found that TM (transverse magnetic) waves incident at small angles with the vacuum-plasma interface couple into the plasma provided that ω/ω ci ≲ 20. Assuming that coupling to the lower-hybrid resonance in the cold-plasma approxima­tion is an indication of accessibility to the ion-cyclotron-harmonic waves in the hotplasma case, an alternative statement of the results obtained is that efficient coupling is possible from the second till the twentieth harmonic of the ion gyrofrequency using an antenna that launches TM waves at an approximately grazing incidence on the plasma surface. Simple configurations for coupling rf energy into thermonuclear plasma are suggested.

Three experiments are described in which the relative motion of media or structures causes nonreciprocal effects of first order in ν/c. The first two experiments deal respectively with the Fresnel effect due to the motion of a normal dielectric and the electron drift in the plasma of a glow discharge. The third experiment is a microwave analogon to the historical experiments of Harress, Pogany and Sagnac. To our knowledge these are the first investigations of the well-known effects under conditions where the transverse dimensions of the waves are comparable to the wave length. Under such conditions the nonreciprocal effects when expressed in fringe shifts (or phase angle) remain small. They could, however, be detected after the development of an elaborate microwave interferometry which could resolve fringe shifts down to the order of 10 -6 .

In order to calculate the electrical conductivity of a plasma an approximate formula has been derived which is based on an improvement of the expression corresponding to a Lorentzian gas. The deviation from the exact solution (which is based on the Boltzmann equation of a plasma) is in most cases lower than 5% and will exceed this deviation only in exceptional cases. The calculations have been performed for xenon and neon.

An analysis of the plasma state was performed by determination of the electron temperature and the distribution temperature from end -on intensity measurements in the arc axis and by determination of the heavy particle temperature from measurements of the electrical field strength. The electrical current of the arc was varied between 1.5 amp and 60 amp and the argon pressure was varied from 0.2 atm to 5.0 atm. It turned out that not the electron density but the mean free path of the electrons is the essential parameter for the adjustment of LTE. Moreover radial end-on intensity measurements of Ar-I lines with different upper energy levels revealed significant intensity anomalies spreading from the axis of the arc to the walls. These effects could be explained assuming that a diffusion of Ar atoms, which are excited to 4s-levels, takes place out of the arc axis. The diffusion equation and its solution led to a satisfying explanation of the observed radial non-LTE effects.

A body of arbitrary convex shape and uniform temperature is thought to be placed in a freemolecule gas flow. In the near-equilibrium regime the four Knudsen accommodation coefficients suffice to express the drag and absorbed heat flux. Extensions to higher speeds require more information − or assumptions − on the gas-surface interaction, as is made clear by the case with Ma ≫ 1.

The thermodynamic properties of excimer formation process of αNPO in dioxane, methyl methacrylate, toluene, ethyl ether, acetone and acetonitrile have been determined. It has been found that the changes of entropy and enthalpy in the excimer formation process are smaller in all polar solvents than in nonpolar solvents. This effect can be explained by the influence of dielectric constant of solvent on the excimer stability of αNPO.

Mixtures of cholesterogenic compounds of opposite helical twisting power at a definite temperature T n behave like a nematic liquid crystal (compensated mixtures). Using lecithin treated quartz plates nematic mesophases form a homeotropic texture with the optical axes perpendicular to the quartz surface. Thus, in compensated cholesteric mixtures the long axes of the molecules at T n switch by an angle of 90°. The orientation of the cholesteric solvent molecules is transferred to rodlike solute chromophores also switching at T n . By measurements of the change of absorptivity or fluorescence intensity of the solute chromophores at T n one can determine the direction of the transition moment with respect to the molecular axes. This effect has been tested in the case of chromophores with transitions of different polarization.

The ion components of the mercury argon low pressure discharge are analysed with help of a quadrupole mass spectrometer. Here we have found besides the main components Hg + and Ar + the diatomic ion-molecules Hg 2 + , Ar 2 + and ArHg + . With a discharge current of 200 mA, argon pressure 0,2 torr and mercury vapour pressure 2.8·10 -3 torr, the ion components are in the ratio [Hg + ] : [Ar + ] : [ArHg + ] : [Hg 2 + ] : [Ar 2 + ] = 1000:134:24:10:3 . The ratios i(ArHg + ) |i (Ar 2 + ), i (Ar + ) |i (Hg + ), i (Ar 2 + ) |I (Ar + ), i (Hg 2 + ) |i (Hg + ) of the effusing ion currents are measured as a function of mercury vapor pressure, discharge current and argon pressure. These measurements yield the following formation processes of ArHg + and Ar 2 + : For the products of reaction rates k and lifetimes τAr m , τAr* of the metastable and highly excited Ar-atoms, we get k ArHg + ·τ Ar m = 61·10 -16 cm 3 , k Ar 2 + · τ Ar*= 1.1·10 -16 cm 3 . So the following cross sections are found: σ ArHg + = 5.8-10 -15 cm 2 , σ Ar 2 + = 3.6-10 -15 cm .

In nonstoichiometric barium titanate ceramics an excess of TiO 2 leads to the formation of a second phase completely covering the individual grains. For that reason even a small amount of the second phase causes a strong decrease of the permittivity of the ceramic material.

The apparent effective diarge Z** of 125 Sb, 113 Sn, 110 Ag, 58 Co, 59 Fe and 54 Mn has been measured in polycristalline paramagnetic nickel, using the thindayer technique. The atom transport appears to be directed toward the cathode for all the investigated solutes. For left-hand impurities, this effect is interpreted as due to predominant d-hole scattering on the impurity; for right-hand impurities both the direct field effect and d-hole scattering have an influence on the direction of the transport.

The effect of non-chiralic solute molecules on the pitch of cholesteric mixtures of cholesteryl chloride and cholesteryl nonanoate has been studied as a function of the composition and the temperature. The occurrence of a pretransition to the smectic state at low CC content is established. In the pretransitional state the pitch decreases exponentially with increasing temperature and is extremely sensitive against the addition of most organic molecules. In the normal cholesteric state the pitch increases with increasing temperature. In this state only a very limited number of nonchiralic molecules exert an appreciable influence on the pitch.

In part B we deal with some applications and conclusions of the theory for collective rotations of quantum mechanical systems which has been treated in part A. In the first section we investigate the consequences of a body-fixed coordinate-system lying in the principal axes of inertia. We find that for this choice in general no specific decoupling is obtained, and therefore the so-called hydrodynamic moments of inertia are always a lower limit for the real moments of inertia of a system. Further the transition from a n-body system to the rigid body is carried out. In another section the symmetry conditions of systems with identical particles are treated. Especially we study the question how to define the optimal body-fixed frame of reference in a system of independent identical particles. Finally we compare the results of our exact theory of collective rotations with the results of the cranking model and find that only in the limit of an infinitely heavy core the cranking model leads to an exact expression for the moment of inertia.

We are concerned with the formulation of the essential features of quantum theory in an abstract way, utilizing the mathematical language of proposition lattice theory. We review this approach giving a set of consistent axioms which enables to achieve the relevant results: the formulation and the essential role of the superposition principle is particularly examined.

Flow birefringence in molecular gases is due to a collisional alignment (tensor polarization) of the rotational angular momentum of the molecules in the presence of a gradient of the flow velocity. The reciprocal phenomenon is an anisotropy of the velocity distribution caused by an externally maintained tensor polarization. The kinetic theory of this new effect is presented and methods for its experimental detection are indicated.

The ratio of the Larmor frequencies of 43 Ca and 37 Cl has been measured and a magnetic moment for 43 Ca of μ( 43 Ca 2+ in D 2 O) = -1.315645 (7) μN; has been calculated. 43 Ca chemical shifts have been determined in aqueous calcium salt solutions with 43 Ca in natural abundance, also at low concentrations. The latter result is interesting for 43Ca studies in biological systems.

The bonding in the F5SO - -ion is discussed by comparing the results of CNDO MO calculations on this and some related compounds with data obtained from IR- and RAMAN-spectra. Theoretical and experimental results are found to be in good agreement. The-yet not prepared -acid F 5 SOH is discussed with respect to its stabilization and acidity.

The linear thermal expansivity of polycrystalline silver iodide has been measured with a "Fused-Quartz Tube" apparatus in the temperature range 170 - 500 °C, the mean linear thermal expansion coefficient being α t 180 =(2.607 + 0.00182 t) 10 -5 (°C -1 ). An irregular change in the thermal expansivity was found close to 432 °C where an order-disorder transition has been reported.