Band 32, Heft 2

A practical method for the calculation of canonical exponential transformations in closed analytic forms is presented. An application to an antiresonant electron-phonon system is given. In particular the optical zero phonon line is calculated, which reflects the resonant nature of the system

Commencing from qualitative ah initio calculations on the molecules benzene, toluene and fluorobenzene, the corresponding favoured positions of electrophilic substitution are discussed in terms of perturbation theory including the electrostatic molecular potential and polarisation

The rotational transition J=2 → 3 of RbBr at 8.4 GHz was measured. The analysis of the hyperfine structure resulted in the quadrupole coupling constants of the isotopic species 85 Rb 79 Br, 85 Rb 81 Br, 87 Rb 79 Br, and 87 Rb 81 Br in the ground vibrational state. From the observation of 85 Rb 79 Br in the excited vibrational states υ = 1 and 2 the vibrational dependence of the quadrupole coupling constants was derived: e qυ Q( 85 Rb) = (-47.20 + 0.28(υ+1/2) ±0.25) MHz; e qυ Q( 79 Br) = (3.08 + 0.75 (υ+1/2) ±0.30) MHz

By Fourier transform NMR spectroscopy the 55 Mn and 95 Mo resonance lines in the different permanganate and molybdate species Mn 16 O 4-n 18 O n - and Mo 16 O 4-n 18 O n 2- {n = 0, 1, 2, 3, 4) have been resolved in aqueous solutions of potassium permanganate and sodium molybdate. An isotopic effect on the Larmor frequency for 55 Mn of (0.59 ± 0.02) ppm and for 95 Mo of (0.25 ±0.01) ppm to lower frequency has been found for the substitution of one 160 atom by one 180 atom. The relaxation rates 1/T 1 of 55 Mn in the different lines of the permanganate solution are equal within the limits of error. The oxygen exchange rate for the water-permanganate system has been evaluated

17 O and 2 H Fourier transform NMR studies have been made in water with varying contents of hydrogen isotopes. Chemical shifts of 17 O as a function of 2 H contents and as a function of the hydrogen ion concentration are given. The ratios of the Larmor frequencies of 17 O and 2 H in water are used for evaluation of a magnetic moment of 17 O in water. The deuterium isotope effect on the 17 O NMR line in water is (3.08 ±0.20) ppm to lower frequency for deuterium oxide. No 17 O shift was found in deuterium oxide with high 18 O enrichment

The quadrupole splittings in the deuterium NMR spectrum from single crystals of deuterated sodium Perchlorate monohydrate, NaClO 4 -D 2 O, have been measured at 25 °C and - 55 °C. At room temperature, the 180° flip frequency of the D 2 O molecules is large compared to the difference between the splittings for the two deuterons. The average quadrupole coupling constant (e 2 q Q/h) and asymmetry parameter η are 134.1(4) kHz and 0.621(5), respectively. At -55 °C, the electric field gradient tensors for each of the two deuterons were observed corresponding to slowly flipping water molecules, and e 2 qQ/h and η for the two deuterons are 231.5(6) and 226.7(6) kHz and 0.196(4) and 0.195(5), respectively. The results indicate that the hydrogen positions in NaClO 4 -H 2 O are dynamically disordered

In studying the radiationless energy transfer between unlike molecules (heterotransfer) in fluid and rigid solutions the fluctuations of the concentration of the acceptor molecules, as well as the dependence of the probability of resonance excitation energy transfer on the mutual orientation of the transition moments of the interacting donor and acceptor molecules have been taken into account. With these and the assumptions of the shell model of a luminescent centre (A. Kawski and J. Kaminski, Z. Naturforsch. 29 a, 452 [1974]) one obtains the Förster expression for the quantum yield of the donor fluorescence quenched by foreign absorbing substances

Results of the depth profiling of a laser mirror are reported and discussed. The sample was bombarded with 40 Ar + , 32 O 2 + and 16 O - in order to establish optimum conditions. It was found that the bombardement by means of 16 O - results in the best depth concentration profile

The electrical resistivity of Ni is derived from time-resolved measurements of current and voltage of exploding Ni-wires, which are part of a fast RCL-discharge circuit. The values of the resistivity at the Curie-point and at the melting point are in good agreement with stationary measurements. Deviations are discussed. Furthermore, the energy dependence of the resistivity of liquid Ni up to the boiling point (at normal conditions) is determined and compared with the temperature dependence assuming a constant specific heat

Results of a microwave investigation of the molecules 2-Cyanothiophene and 2-Cyanofurane are reported. The microwave spectrum of 2-Cyanothiophene was examined in the frequency range of 13 -40 GHz mainly to get a more accurate rotational constant A from the assignment of μ b -btransitions. From the resolved hyperfine structure due to nuclear quadrupole coupling of the 14 N-nucleus the quadrupole coupling constant X + =X bb + X cc was determined for 2-Cyanothiophene. No information for X - was available from the measured transitions. From Stark effect studies the dipole moments were determined for both molecules. The nuclear quadrupole coupling as a perturbation of the second order Stark effect was included in the Stark effect analysis

The classical problem of radiative transfer in a spectral line, due to two-level atoms, in a homogeneous medium is reconsidered. It is pointed out that the source function used up to now in the literature neglects the diffusion of the excited atoms. In many cases this assumption is not justified. In the low-temperature limit kT ≪ hv, the correct source function, allowing for diffusion of excited atoms, obeys an integro-differential equation

The formation in the solid state of CaWO 4 from CaO (single crystal) or Ca 3 WO 6 and WO 3 was investigated by the contact method between 800 and 1000 °C in air and in argon. The results obtained indicate that these reactions are governed by the diffusion of the W 6+ and O 2- ions. From the CaWO 4 structure, along with the lattice disorder predominant in this compound (0 vacancies and 0 interstitials) and the values of ionic mobilities, it was possible to state that the oxygen diffusion, via V 0 2· , represents the rate - determining step in the considered reactions

For temperatures above the Neel-point the existence of antiferromagnetic clusters in MnF 2 is established by magnetic resonance. In the temperature range between 80 K and 440 K the ESRintensity is quantitatively described by a cluster model. The excitation energy is computed to be about ΔE = \10 cm -1 . It is shown that the bonding within this antiferromagnetic cluster originates in isotropic exchange interaction between next nearest neighbours, as the model gives a coupling constant of J = 1.21 ±0.07 cm -1 . The connection with exchange effects of exciton states is established

In an Argon-Magnesium-Plasma and a Xenon-Magnesium-Plasma number densities of the four lowest excited levels in Magnesium II were measured using a special absorption method and the absolute spectral line intensities from an optically non-thin layer. Near-Resonant-Charge-Exchange is demonstrated experimentally between Argon ions and MgII(4s 2 S) and between Xenon ions and Mgll (3p 2 P o ), respectively

The dependence of the fluorescence ability on the derealization of electrons in excited singlet states is discussed. It is shown that mainly those states fluoresce in which the electrons are most delocalized. The derealization can be described by Julg's Parameter A

The Navier-Stokes equation of viscous drainage over a naturally permeable wall is investigated. It is found that as an effect of porosity, the film falls faster than that in the clear zone

The microwave rotational spectrum of Nitric Acid has been analysed in the frequency region 8000-35000 MHz and up to J=12. The analysis gives refined rotational constants and all the quartic centrifugal distortion constants

In n-propanol the limiting ionic conductance of Na + was found to be 10,36 cm 2 Ω -1 mol -1 at 25 °C from conductivity- and transference measurements of NaBr and NaJ by use of the radioisotope method

In pure water the limiting ionic conductance of (½ UO 2 2+ ) was found to be 57 cm 2 Ω -1 mol -1 by use of conductivity measurements of UO 2 (ClO 4 ) 2 • xH 2 O in diluted perchloric acid

In the n-propanol UO 2 (NO 3 ) 2 ·2 H 2 O-System the limiting ionic conductance of (½ UO 2 2+ ) was found to be 15,94 cm 2 Ω -1 mol -1 at 25 °C, its association constant being 5,2·10 9 ι 2 ·mol -2

Shell model calculations have been carried out to estimate the barrier heights to migration of ions in alkali halides by employing Sangster's parameters. The calculated values are in good agreement with experiment

Observations, data and assessments concerning atmospheric N 2 O are reviewed, in order to present the current state of knowledge on this subject. Background information from microbiology, soil science, and oceanography is provided to facilitate understanding of the complicated processes in soil and water which are responsible for the release of N 2 O to the atmosphere. The problem of increasing use of industrial fertilizers and combustion of fossil fuels is discussed in so far as atmospheric N 2 O is concerned