Volume 34, Issue 9

It is shown that the dispersion functions of coupled waves depend very sensitively on the dielectric dispersion in the visible frequency region. The dispersion functions of all six coupled waves can be described by explicit formulae in very good approximation.

The profile of the H β line emitted from an afterglow plasma in pure hydrogen gas and a mixture of hydrogen and helium has been measured in axial direction using a multichannel spectrum analyzer with additional temporal resolution. Measurements were performed without and with a superposed magnetic field (B ≦ 10.8 Tesla) in axial direction. With magnetic field we observed a rather strong dependence of the wavelength positions of the two lateral "Zeeman components" (intensity maximum due to combined Stark-Zeeman effects). This feature is important in radiative transfer calculations and for the spectroscopic determination of magnetic fields in plasmas. - Both with and without magnetic field we always observed a line structure superposed on the H β profile. The structure disappeared in an active electrical discharge and changed with gas composition. The line structure is interpreted as being due to electronic transitions of molecular hydrogen. It is very probable that the "satellite structures" of Balmer lines observed by other authors under quite different experimental conditions and interpreted as dynamical Stark effect splitting due to fluctuating electric fields have in most cases the same molecular origin. Our earlier published line profiles of Hβ for B = 0 [J. Ramette and H. W. Drawin, Z. Naturforsch. 31 a, 401 (1976) ] are revised in the present paper.

Measurement of the Hel line at λ = 447.15 nm during the recombination of a helium plasma in a magnetic field of induction B = 10 Tesla by means of a multichannel analyzer system with spectral and temporal resolution showed a Stark-Zeeman broadened line with a superposed line structure. - There are sufficient experimental indications to conclude that this structure is due to molecular transitions, in agreement with the observations for magnetic field-free afterglow plasmas. At the lowest electron densities also some of the weaker Zeeman components of both the allowed and forbidden transitions probably contribute to the structure. The existence of Baranger-Mozer plasma satellites under our experimental conditions could not be confirmed. - We observed further a relatively strong electron density-dependent asymmetry in the intensities of the two main lateral Zeeman-Stark components of the allowed line.

The influence of light pressure on plane and spherical plasma flows is treated. Numerical calculations show that smooth laser pulses lead to formation of an overdense plateau if thermal transport is non-negligible there, and that an originally supersonic flow becomes subsonic in this region. The results are consistent with analytical considerations. Density humps, as reported in the literature, are found in conjunction with spiking pulses or prepulses only.

AC electric fields ware applied to suspensions of giant lecithin vesicles observed under a phase contrast microscope. Elongated vesicles were found to align parallel to the field. In sufficiently strong fields the vesicles opened at both ends and became cylinders which in some cases were immutable under further increase of the field. The cylinder parameters can be used to calculate the edge energy of the cylinder wall. For the single bilayer we obtain 2-10 -6 erg cm -1 .

Quantum chemical investigations of the electric dipole moments in the ground and excited states and also transition moments of 2,2′-p-phenylenebis (5-phenyloxazole) (POPOP) and 2,2′-p-phenylenebis (4-methvl-5-phenylaxazole) (2MPOPOP) were carried out with the PPP-CI-method. It was established that the transition moments of POPOP and 2MPOPOP are parallel to the long axis, whereas the electric dipole moments are mutually parallel and perpendicular to the long axis of these molecules. Further, the emission anisotropics r of the fluorescence of the prolate molecules POPOP. 2MPOPOP and the non-polar diphenvlenestilbene (DPS) in solvents of different viscosities η were investigated. Also for these substances the non-linear dependence of 1/r on T/η was confirmed. This deviation from the linear dependence is stipulated essentially through the length of the molecule. The effective volumes and the rotational relaxation times in different solvents of the studied molecules were determined.

It is shown that the solvent dependence of the fluorescence wavenumber and decay time as well as the solvent dependent effect of an external electric field on the absorption and fluorescence spectra of 4-(9-anthryl)-N,N-dimethylaniline can be fully understood taking into account reaction field induced polarizability effects.

The dynamical properties of an aqueous ammonium chloride solution have been calculated from a molecular dynamics simulation over 3.5 picoseconds at a temperature of 301 K where the basic periodic cube contained 200 water molecules, 8 ammonium ions and 8 chloride ions. The effective pair potentials are based on the ST 2 water model, a rigid tetrahedral four point charge model for NH 4+ , and a single point charge model for CI - . The coefficients of self-diffusion and of rotational diffusion, the spectral densities of hindered translations and of librations, the correlation times of the dipole moment vector and the vector connecting the two protons in a water molecule are reported separately for the various subsystems - NH 4+ , Cl - , bulk water, hydration water of NH 4 + and CI - - and are compared with the available experimental data. Implications with respect to the structure breaking ability of the ions are discussed.

The radical yield in the electron transfer reactions between thionine triplet and various halogenanilines, as measured by kinetic flash spectroscopy in the microsecond time region, decreases by application of magnetic fields up to 4 kGauss. The relative magnetic field effect parallels the influence of the heavy atom substituents on the intersystem crossing rate constant in the triplet exciplex supposed to be the primary product of the electron transfer reaction. The magnetic field effect is suggested to be due to differences of the g-factors in the geminate radical pair, originating by dissociation of the triplet exciplex.

Luminescence spectra at 85 K have been recorded for a series of chromium (III) complexes with alkyliminodiacetates (RIDA) of the form K[Cr(RIDA) 2 ], R=M(methyl), E(ethyl), n-P(n-propyl), i-P(isopropyl), n-B-(n-butyl), and t-B (t-butyl). Infrared and far infrared spectra of room temperature samples were also recorded. All of the RIDA complexes exhibited the vibronic spectrum, with a remarkable shift of the intensity maximum away from the zero phonon line, which is characteristic of trans geometry in these complexes pointing to a 2 E (tetragonal symmetry label) luminescent state. A comparison of vibronic intervals with IR data suggests several bands which may be indicative of iminodiacetate coordination.

The Gauss-perturbed harmonic oscillator, a customary double minimum potential of molecular spectroscopy, is made more flexible by addition of a term α4 · exp(-γ 4 X 4 ). The matrix elements of the additional term are calculated in the harmonic oscillator basis in terms of parabolic cylinder functions. A sum rule for matrix elements serves as an independent numerical control. The eigenvalues can be given by straightforward diagonalization of the Hamilton-matrix. In addition, upper and lower bounds are given for the partition function.

The kinetics of Lithium Formate Monohydrate (LFM) dehydration (single crystal samples) has been investigated at constant temperature (317 < T < 353) under dynamic vacuum both optically and thermogravimetrically. The process takes place with an induction period followed by a constant rate period. The first one is characterized by a surface nucleation which occurs mostly in connection with dislocations emerging on the (021), (110) and (010) faces and at the vertex-intersections of these planes; the second one corresponds to the advancement of a reaction interface (formed on the planes with l ≠ 0) along the c-axis. This topochemical model has been interpreted on the basis of the different features of the actual dislocations and of the reticular geometry of the LFM crystal.

The 1 : 1 adduct compounds which are the prevailing vapour species over equimolar mixtures of AlkF and AlF 3 (Alk = Li, Na, K, Rb and Cs) in the temperature range 450-750°C have been isolated in argon and nitrogen matrices and examined bv infrared spectroscopy. Seven frequencies which are assigned to matrix isolated alkali tetrafluoroaluminate molecules have been found for all systems investigated. Group theoretical analysis and subsequent normal coordinate computations of the reassigned frequencies confirm a structural model for the AlkAlF 4 molecules having the symmetry C 2v -However, the results from this analysis cannot be taken as a definite confirmation of a true bidentate structure for these molecules in the vapour phase. The alkali metal-fluorine bond is found to be rather weak, and the Al-F terminal bond is found to be stronger than the Al-F bridge bond. Qualitative relations between matrix as well as vibrational shifts and potential energy distribution are discussed.

A gas electron diffraction study of 2-methyloxacyclobutane has been carried out at room nozzle temperature. The four membered ring takes a planar conformation. The mean r a values for the O-C, C-C and C-H bonds are 1.448(5)A, 1.534(4)A and 1.118(3) Å, respectively. The endocyclic bond angles are C-C-C = 85.5(18)° and C-C-O=91.2 (15)°, while the angle C-O-C was assumed to be 92°. The position of exocyclic carbon atom was characterized, in addition by < C exocyclic -C-O = 110.7(7)° and torsional angle C exocyclic -C-O-C = 59.6(40)° (0° corresponds to the anti position of C exocyclic -C and O-C bonds).

In a redox system consisting of 5 × 10 -5 mol dm -3 Ru(bpy)3 2+ complex, 4 × 10 -3 mol dm -3 methylviologen and 5 × 10 -3 mol dm -3 EDTA in aqueous solutions (pH = 3 to 8.5) without catalyst, hydrogen is formed under illumination with light λ > 360 nm. The highest yield was established in the pH-range between 4 and 5. The degradation of the components by prolonged use was studied spectroscopically. For comparison hydrogen evolution was also studied replacing EDTA by TEA or SCN - , respectively, in the above mentioned system.

We investigate if the limits p → 0 or p → 1 for large percolation clusters at concentration p correspond to large lattice animals for fixed size s or fixed perimeter t, respectively. A numerical analysis for the asymptotic number of lattice animals with fixed large perimeter shows that the limit s → ∞ can be interchanged with the limit p → 0, but the two limits t → ∞ and p → 1 cannot be interchanged.

A characteristic change in the vibronic structure of the phosphorescence spectrum is the most sensitive external heavy-atom effect observed with coronene. A linear correlation exists between this vibronic effect and the increase of the phosphorescence/fluorescence quantum yield ratio. The observed decrease of the coronene phosphorescence/fluorescence quantum yield ratio in the presence of rare earth chlorides is probably due to an intermolecular energy transfer from the excited coronene molecule to the rare earth ion.

Comparison of the solutions of the Dirac equation with the corresponding solutions of electrodynamics.