Volume 47, Issue 5

The equipartition frequency ν of an anisotropic plasma is calculated numerically and analytically within the Landau approach for strong magnetic fields and several new integral expressions for ν are presented. In the ultra strong magnetic field case, when r c ≪b, where r c is the Larmor radius and b the classical distance of closest approach, ν is shown to be dependent on how the Coulomb force is cut off at short distances. None of the obtained expressions, however, coincides with experiment, in contrast to the strong interaction theory of O'Neil and Hjorth. For weaker, but still strong magnetic fields ( r c >b) the ambiguity disappears and the weak interaction result describes well the experiment. It is, hence, the transition region r c ≈ b , where the transition from strong to weak interaction takes place

A whole body NMR imager (1.5 T) has been operated with large samples and a home built coil to study NMR signals of heteronuclei at very low concentrations. Typical examples of 27 Al, 51 V, and 81 Br are given, signals of 1 µmolal aqueous solutions of e.g. NaVO 3 can be detected. 129 Xe was observed in xenon gas at atmospheric pressure with one scan. A 129 Xe gaseous state NMR image is presented in a xenon containing sample. Also some typical measurements of longitudinal relaxation times of 27 Al, 51 V, and 129 Xe are given

Fluorescence Spectroscopy on UHV-Deposited Thin Films of Coronene Thin films of coronene, UHV-deposited on different inorganic substrates (Si(111), Si(100), Si/Si0 2 , graphite(0001) and MoS 2 (0001)) have been investigated via laser induced fluorescence and fluorescence excitation spectra at various coronene coverages (from submonolayers to 1000 Å) and temperatures (4.2 K - 300 K). Independent of the substrate the films reveal a characteristic absorption which is red-shifted with respect to that of the coronene crystal and is attributed to a new film-specific structural modification (in accord with X-ray data). At film thicknesses d > 50 Å this absorption is increasingly superimposed by crystal-type absorption. The fluorescence spectra at low coverages and low temperatures strongly depend on the substrate. On Si/Si0 2 , graphite and MoS 2 the fluorescence is similar to that of the coronene crystal. Thin films on Si(100) and Si(111), on the other hand, show monomer-like narrowband fluorescence originating, presumably, in substrate-induced trap states

New Far Infrared Laser Magnetic Resonance (LMR) spectra have been detected in the reaction of Cl atoms with CH 2 CO. Based on chemical and kinetic evidence they were assigned to CH 2 Cl radicals. The assignment was substantiated by subsequent experiments which employed the reactions of F atoms with CH 3 Cl and Na atoms with CH 2 Cl 2 , respectively. The three different sources yielded identical spectra

This article describes a few aspects of NMR characterization of half-integer quadrupolar nuclei in powder samples which are either static or rotating around one fixed axis (M.A.S. and V.A.S. techniques). The simultaneous occurence of C.S.A. and quadrupole interactions with possible noncoincident tensors is discussed. Two experimental limitations are taken into accout: the sample spinning speed and the RF-amplifier power

The surface tension around the eutectic composition of molten binary and ternary mixtures composed of Li 2 CO 3 with Na 2 CO 3 and/or K 2 CO 3 has been measured by the maximum bubble pressure method. The surface tensions of all the three systems were represented as functions of temperature

The dielectric relaxation spectrum of the title substance in mixtures with 1,4-dioxane or benzene (pure liquid to moderate mixture ratios) is measured between 5 MHz and 36 GHz at 20°C. The static permittivity is determined over the whole mixture range. The results are discussed in particular with respect to the possibility that different types of hydrogen bonded aggregations may contribute to the main relaxation

The rotational spectrum of the fluorobenzene-argon complex has been studied in the microwave region between 7 and 18 GHz using a pulsed molecular beam microwave Fourier transform spectrometer. The rotational constants were found to be A = 1811.81369(11) MHz, B= 1105.12965(15) MHz, C = 901.84281(5) MHz, the centrifugal distortion constants are Δ J = 2.6886(17) kHz, Δ JK = 8.3761 (52) kHz Δ JK = -8.278(5) kHz, ρ J , =0.65993(72) kHz, and ρ K = 6.013(11) kHz. The argon atom is placed 3.55 Å above the ring plane

The reverse Monte Carlo simulation has been tested by modelling the partial distribution functions of amorphous Ni 2 Zr. Three runs of simulation involving experimental data from isotopic substitutions neutron scattering and X-ray anomalous scattering are presented

The molecular dynamics of tetramethylstibonium hexafluorophosphate, [Sb(CH 3 ) 4 ]PF 6 , is investigated over a broad temperature range. NMR spin lattice relaxation times T 1 and the NMR second moments of the 1 H and 19 F nuclei were determined in the range 8.6 ≦ T/K ≦ 332.3 for polycrystalline [Sb(CH 3 ) 4 ]PF 6 . The complex cation undergoes isotropic tumbling for T > 260 K and thermally activated methyl group rotation in the temperature range T < 196 K. The activation energies for the transition from methyl group rotation to cation reorientation, as derived from NMR wideline (18.1 kJ/mol) and relaxation (22.7 kJ/mol) measurements, match. At very low temperatures pseudo classical line narrowing is observed, indicating tunneling motions of the methyl groups. The existence of two crystallographically inequivalent methyl groups is found by X-ray structure analysis at room temperature. The space group is P6 3 mc, Z = 2; a = 738.6 pm, c = 1089.3 pm. It is confirmed by two steps in the temperature dependence of the signal intensity of the quasielastic line in neutron fixed window measurements in the temperature range 2 < T/K <148. The low temperature spin lattice relaxation times can be explained qualitatively by contributions of two crystallographically inequivalent methyl groups. Apparent activation energies for the two crystallographically different methyl groups are estimated. The complex anion undergoes isotropic tumbling in the temperature range 95 < T/K < 330. Above 330 K additionally translational motion is activated. Below 95 K the rotational motion of PF - 6 is freezing in via an uniaxial state in range 40 < T/K <80. Activation energies for both isotropical tumbling (10.5 kJ/mol) and uniaxial rotation (5.8 kJ/mol) have been derived from 19 F NMR spin lattice relaxation

The local environment of Ti 3+ cations in methanol solutions and in Nafion perfluorinated ionomers swollen by water and methanol has been studied by electron spin resonance (ESR) and by 1 H and 2 H electron nuclear double resonance (ENDOR) spectroscopies. The two major sites reflecting the ligation of the cations as a function of solvent structure and cation concentration have been analyzed, using whenever possible the method of orientation selection for the ENDOR transitions. The distance R N of the protons from the central cation, and the angle Θ N between the symmetry axis of Ti 3+ and the Ti 3+ -proton vector have been deduced by evaluating the dipolar interaction tensor and by simulating the orientation dependence of the ENDOR signal. For site 1 of Ti 3+ in methanol (g ॥ = 1.986 and g ⊥ = 1.894) no orientation selection was possible, and R N values in the range 4.1 to 4.6 Å are suggested from the ENDOR splittings. For site 2 of Ti 3+ in methanol (g ॥ = 1.943 and g ⊥ = 1.960) equatorial and axial methyl protons have been detected; the R N values deduced from the simulations are 3.95 and 4.35 Å, respectively. For Ti 3+ in Nafion swollen by water (g || = 1.997 and g ⊥ = 1.907), equatorial and axial protons from OH groups have been detected, and the ENDOR spectra were simulated with RN values of 2.60 and 3.10 Å respectively for these protons