Precise - and -factor measurements of Ba+ isotopes

Laser-microwave double and triple resonance experiments were performed on clouds of Ba⁺ ions confined in a Penning ion trap to induce and detect electronic and nuclear spin flip transitions. Collisions with buffer gas molecules in the trap was used to reduce the lifetime of a long lived metastable state of the ions, in which population trapping might occur, and to cool the ions to the ambient temperature. Loss of ions from the trap by collisions were prevented by coupling the magnetron and reduced cyclotron motions by an additional r.f. field at the sum frequency of the two motions. Electronic Zeeman transitions in ¹³⁸Ba⁺ and ¹³⁵Ba⁺ were observed at a full width of about 3 kHz at a transition frequency of 80 GHz. The uncertainty of the line center was . From the magnetic field calibration by the cyclotron resonance of electrons stored in the same trap the g_J-factor for both isotopes could be determined to . From radiofrequency induced transitions of ¹³⁵Ba⁺ the nuclear g-factor could be determined . Both measurements improve earlier results by about one order of magnitude. Received: 9 July 1998 / Accepted: 14 July 1998     

Trajectories of Charged Particles in Radial Electric and Uniform Axial Magnetic Fields

The trajectories of charged particles were determined over a wide range of parameters characterizing the motion in cylindrical low-pressure gaseous discharges and plasma-heating devices which have steady radial electric fields E perpendicular to uniform steady magnetic flelds B. Three radial distributions of E were considered: E ? r, constant E, and E ? r-1. These distributions are characteristic of the fields measured in a modified Penning discharge, in two NASA Lewis Bum-out-type plasma-heating devices, and that estimated for the Ixion device, respectively. The plasmas of such ? × B? devices are often characterized by their high ratios of drift energy to mean particle energy, finite gyroradius effects, and sizeable electric field changes in the distance covered by a cyclotron radius. Such particle motions are not amenable to simple guiding center theory. From numerical calculations of the actual trajectories it was concluded that the differences between cyclotron frequency and qB/m, and between azimuthal drift and a guiding center approximation (including ? × B? and centrifugal force terms) are appreciable. The net cyclotron motion obtained by subtracting the actual drift from the trajectories, however, has a nearly circular contour over which the speed is quite constant.     

Magneto-optical trapping of bosonic and fermionic neon isotopes and their mixtures: isotope shift of the 3P2 ↔ 3D3 transition and hyperfine constants of the 3D3 state of 21Ne

We have magneto-optically trapped all three stable neon isotopes, including the rare ²¹Ne, and all two-isotope combinations. The atoms are prepared in the metastable ³P₂ state and manipulated via laser interaction on the ³P₂ ? ³D₃ transition at 640.2?nm. These cold (T ≈ 1?mK) and environmentally decoupled atom samples present ideal objects for precision measurements and the investigation of interactions between cold and ultracold metastable atoms. In this work, we present accurate measurements of the isotope shift of the ³P₂ ? ³D₃ transition and the hyperfine interaction constants of the ³D₃ state of ²¹Ne. The determined isotope shifts are (1625.9 ± 0.15)?MHz for ²⁰Ne ? ²²Ne, (855.7 ± 1.0)?MHz for ²⁰Ne ? ²¹Ne, and (770.3 ± 1.0)?MHz for ²¹Ne ? ²²Ne. The obtained magnetic dipole and electric quadrupole hyperfine interaction constants are A(³D₃) = (?142.4 ± 0.2)?MHz and B(³D₃) = (?107.7 ± 1.1)?MHz, respectively. All measurements give a reduction of uncertainty by about one order of magnitude over previous measurements.     

Nuclear spin–lattice relaxation and complex motion of macromolecules in solution

The NMR spectral densities of a complex motion consisting of a combination of anisotropic overall motion and internal motion have been derived. Two approximations of the equations derived for the cases of slow, J_slow (ω), and fast, J_fast (ω), internal motions are presented. These equations imply that reduction in spectral density of overall motion can be observed if the maxima of internal and overall motions spectral densities versus temperature are well separated, as for fast internal motion. Slow intramolecular motion influences the values of spectral densities of the overall motion if one of the two spins performs a motion, for example a proton in double minimum of the ¹⁵N-H?···?N hydrogen bond. The analysis presented reveals small differences between the temperature dependencies of spectral densities of the isotropic and anisotropic overall motions. The theory is illustrated by the ¹³C protonated carbon spin-lattice relaxation of α-cyclodextrin macromolecule, using the expected motional parameters: D _∥/D _⊥?≈?5 at room temperature and for a fast or slow internal motion.     

Water-filled MCM-41 characterized by double-quantum-filtered2H NMR spectral analysis

The dynamics of water molecules confined in adsorbed layers of siliceous MCM-41 with a pore diameter of 2.8 nm is investigated at 230 K by deuteron nuclear magnetic resonance (NMR) relaxation studies including line shapes of theT ₁ process and double quantum filtered (DQF) spectral analyses.²H DQF NMR is a particularly sensitive tool for the determination of the adsorbate dynamics resulting from residual quadrupolar interaction due to the local order. The amount of monolayer water is determined. The monolayer water is composed of two different water components characterized by water, with isotropic reorientational motions, exchanging with water displaying a solid-like spectrum with 4 kHz edge splitting. One may expect that the latter water is situated on surface sites in MCM-41. The restricted wobbling motion of the D-O bond is used to describe its dynamics which is one order of magnitude slower than the isotropic reorientational motion. The order parameter, the motional correlation time, and the exchange rate thus determined provide useful information on the structure and the adsorptive properties of the mesoporous system.     

Crystal structure of cholesteryl 4-[4-(4-n-hexylphenylethynyl)-phenoxy]butanoate – a liquid-crystalline unsymmetric dimer

Cholesteryl 4-[4-(4-n-hexylphenylethynyl)-phenoxy]butanoate, which exhibits the phase sequence: Cr 119.3°C (42.4?J?g^?1) SmA 196.4°C (1.1?J?g^?1) TGB–N* 202.4°C (5.4?J?g^?1) I, crystallizes in the triclinic space group P1 with unit cell parameters: a?=?10.527(1), b?=?13.151(2), c?=?16.991(2)?Å, α?=?86.13(1)°, β?=?98.96(1), γ?=?105.43(1)°, Z?=?2. The crystal structure has been solved by direct methods using single-crystal X-ray diffraction data and refined to R?=?0.0618. There are two crystallographically independent molecules, I and II, in the asymmetric unit. In both the molecules the phenyl rings are planar. The dihedral angle between the two phenyl rings is 12.16° and 18.14° for molecules I and II, respectively. In both the molecules, the six-membered rings of the cholesterol moiety are conformationally very similar. However, pronounced differences are observed in the conformation of the five-membered ring, which is intermediate between half-chair and envelope in molecule I, and half-chair in molecule II. The packing of molecules in the crystalline state is found to be a precursor to the Smectic A phase structure. The molecules in the crystal are held together by van der Waal's interactions.     

Magnetic shielding studies on the alkali molecules Na2 and Cs2 by NMR

NMR in the alkali molecules Na₂ and Cs₂ is performed by the atom-molecule exchange optical pumping method. The shielding differences σ(Na)?σ(Na₂)=(29±16)·10^?6 and σ(Cs)?σ(Cs₂)=(221±12)·10^?6 are obtained. The investigation of the contribution of the valence electron to the magnetic shielding is supported by a NMR experiment in free Cs⁺ ions, which yields the shielding difference σ(Cs)?σ(Cs⁺)=(14±12)·10^?6. These measurements allow an estimation of the spin rotation interaction constant in these molecules.     

Correlation of dielectric properties,Raman spectra and calorimetric measurements of β-cyclodextrin-polyiodide complexes (β-cyclodextrin)2 ·BaI7 ·11H2O and (β-cyclodextrin)2 ·CdI7·15H2O

The frequency and temperature dependence of real and imaginary parts of the dielectric constant (ε′,?ε″), the phase shift (?) and the ac-conductivity (σ) of polycrystalline complexes (β-CD)₂·BaI₇·11H₂O and (β-CD)₂·CdI₇·15H₂O (β-CD?=?β-cyclodextrin) has been investigated over the frequency and temperature ranges 0–100?kHz and 140–420?K in combination with their Raman spectra, DSC traces and XRD patterns. The ε′(T), ε″(T) and ?(T) values at frequency 300?Hz in the range T<330?K show two sigmoids, two bell-shaped curves and two minima respectively revealing the existence of two kinds of water molecule, the tightly bound and the easily movable. Both complexes show the transition of normal hydrogen bonds to flip-flop type at 201?K. In the β-Ba complex most of the eleven water molecules remain tightly bound and only a small number of them are easily movable. On the contrary, in the β-Cd case the tightly bound water molecules are transformed gradually to easily movable. Their DSC traces show endothermic peaks with onset temperatures 118°C, 128°C for β-Ba and 106°C, 123°C, 131°C for β-Cd. The peaks 118°C, 106°C, 123°C are related to the easily movable and the tightly bound water molecules, while the peaks at 128°C, 131°C are caused by the sublimation of iodine. The activation energy of Ba²⁺ ions is 0.52?eV when all the water molecules exist in the sample and 0.99?eV when the easily movable water molecules have been removed. In the case of β-Cd the corresponding activation energies are 0.57?eV and 0.33?eV. The Raman peaks at 179?cm^?1, 170?cm^?1 and 165–166?cm^?1 are due to the charge transfer interactions in the polyiodide chains.     

Fluorescence “Switch on” of Conjugates of CdTe@ZnS Quantum Dots with Al, Ni and Zn Tetraamino-Phthalocyanines by Hydrogen Peroxide: Characterization and Applications as Luminescent Nanosensors

In this study, we have developed a novel nanoprobe for H₂O₂ based on the conjugation of CdTe@ZnS quantum dots (QDs) to different metal tetraamino-phthalocyanine (MTAPc): (M?=?(OAc)Al, {OAc?=?acetate}, Ni and Zn). Chemical coordination of the QDs to the MTAPc resulted in the fluorescence “switch off” of the linked QDs which was associated with Förster resonance energy transfer (FRET). In the presence of varying concentration of H₂O₂, the fluorescence of the linked QDs was progressively “switched on” and the FRET mechanism between the QDs and the MTAPc was disrupted. The sensitivity/limit of detection of the nanoprobe followed the order: QDs-ZnTAPc (2.2 μM)?>?QDs-NiTAPc (4.4 μM)?>?QDs-AlTAPc (9.8 μM) while the selectivity followed the order: QDs-NiTAPc?>?QDs-AlTAPc?>?QDs-ZnTAPc. The varying degree of sensitivity/selectivity and mechanism of detection is discussed in detail.     

Hydration states and metallic intercalation effects in dry DNA

Temperature dependence of the complex dielectric constant at 16.3 GHz has been measured on dry poly(dA)-poly(dT) DNA with Na⁺ counterions under different relative humidity (RH). The rotational motion of sole water dipoles hydrated in PO₂⁻ is detected at low RH, and the collective motion due to water network in major groove is successfully observed at high RH. From the infrared (IR) spectroscopy in dry DNA introducing metallic ions (M-DNA), the symmetric and antisymmetric stretching bands of PO₂⁻ distinctly depend on RH and type of metallic ions. The IR spectral change indicates that the monovalent ions (Li and Na) are arranged in PO₂⁻ though the divalent and trivalent ions connect to the base molecules.     

Hofmeister series and ionic effects of alkali metal ions on DNA conformation transition in normal and less polarised water solvent

Normal and less polarised water models are used as the solvent to investigate Hofmeister effects and alkali metal ionic effects on dodecamer d(CGCGAATTCGCG) B-DNA with atomic dynamics simulations. As normal water solvent is replaced by less polarised water, the Hofmeister series of alkali metal ions is changed from Li⁺ > Na⁺ ? K⁺ ? Cs⁺ ? Rb⁺ to Li⁺ > Na⁺ > K⁺ > Rb⁺ > Cs⁺. In less polarised water, DNA experiences the B→A conformational transition for the lighter alkali metal counterions (Li⁺, Na⁺ and K⁺). However, it keeps B form for the heavier ions (Rb⁺ and Cs⁺). We find that the underlying cause of the conformation transition for these alkali metal ions except K⁺ is the competition between water molecules and counterions coupling to the free oxygen atoms of the phosphate groups. For K⁺ ions, the ‘economics’ of phosphate hydration and ‘spine of hydration’ are both concerned with the DNA helixes changing.     

Spectra of copper and europium β-diketonates in alcoholic solutions and transparent dielectrics

We have used optical and EPR spectroscopy to study the mechanisms for color center formation in nanoporous glasses, polymethylmethacrylate, and alcoholic solutions containing ?-diketonate molecules: Cu(hfac)₂, Ba(hfac)₂, Pr(hfac)₃, and Eu(fod)₃. We have observed and studied the complex structure of the absorption bands in the 300 nm region belonging to the intraligand π-π* transition. Analogous results were obtained when studying the photoluminescence spectra of ⁵D₀ → ⁷F₀ transitions of Eu³⁺ ions and the EPR spectra of Cu²⁺ ions in matrices doped with Cu(hfac)₂. We propose a model according to which for β-diketonate molecules (except for basic diketonates), a hydrolyzed form exists that is formed during synthesis of the polycrystalline powder due to the presence of water molecules. The model allows us to explain the spectral manifestations of β-diketonates in different matrices.     

Modification and smoothing of patterned surface by gas cluster ion beam irradiation

Surface modification and smoothing of patterned surfaces with gas cluster ion beams were studied. In this work, line and space patterns having various intervals and depths were created on amorphous carbon films by focused Ga⁺ ion beams, and subsequently, Ar GCIB irradiations on the pattern were performed. When the acceleration voltage of Ar cluster ions was 20 kV, the grooves, whose interval was below 200 nm, were planarized. However, it required much higher ion dose for wider interval of patterns. It is estimated that the distance of lateral motions induced by one cluster ion impact defines the spatial wavelength dependence of smoothing.     

Superior tolerance of Ag/Ni multilayers against Kr ion irradiation: an in situ study

Monolithic Ag and Ni films and Ag/Ni multilayers with individual layer thickness of 5 and 50?nm were subjected to in situ Kr ion irradiation at room temperature to 1 displacement-per-atom (a fluence of 2?×?10¹⁴?ions/cm²). Monolithic Ag has high density of small loops (4?nm in diameter), whereas Ni has fewer but much greater loops (exceeding 20?nm). In comparison, dislocation loops, ～4?nm in diameter, were the major defects in the irradiated Ag/Ni 50?nm film, while the loops were barely observed in the Ag/Ni 5?nm film. At 0.2?dpa (0.4?×?10¹⁴?ions/cm), defect density in both monolithic Ag and Ni saturated at 1.6 and 0.2?×?10²³/m³, compared with 0.8?×?10²³/m³ in Ag/Ni 50?nm multilayer at a saturation fluence of ～1?dpa (2?×?10¹⁴?ions/cm²). Direct observations of frequent loop absorption by layer interfaces suggest that these interfaces are efficient defect sinks. Ag/Ni 5?nm multilayer showed a superior morphological stability against radiation compared to Ag/Ni 50?nm film.     

Carbon (70 MeV) and copper (120 MeV) ions irradiation effects in Makrofol-N

Makrofol-N polycarbonate was irradiated with carbon (70 MeV) and copper (120 MeV) ions to analyze the induced effects with respect to optical and structural properties. In the present investigation, the fluence for carbon and copper beams was kept in the range of 1×10¹¹– 1×10¹³ ions/cm² to study the swift heavy ion induced modifications. UV–VIS, FTIR and XRD techniques were utilized to study the induced changes. The analysis of UV–VIS absorption studies revealed that the optical energy gap was reduced by 17% on carbon irradiation, whereas the copper beam leads to a decrease of 52% at the highest fluence of 1×10¹³ ions/cm². The band gap can be correlated to the number of carbon atoms, N, in a cluster with a modified Robertson's equation. In copper (120 MeV) ions irradiated polycarbonate, the number of carbon atoms in a cluster was increased from 63 to 269 with the increase of ion fluence from 0 to 1×10¹³ ions/cm², whereas N is raised only up to 91 when the same polymer films were irradiated with carbon (70 MeV) ions under similar conditions. FTIR analysis showed a decrease in almost all characteristic absorption bands under irradiation. The formation of hydroxyl (? OH) and alkene (C?C) groups were observed in Makrofol-N at higher fluence on irradiation with both types of ions, while the formation alkyne end (R? C≡ CH) group was observed only after copper ions irradiation. The radii of the alkyne production of about 3.3 nm were deduced for copper (120 MeV) ions. XRD measurements show a decrease in intensity of the main peak and an increase of the average intermolecular spacing with the increase of ion fluence, which may be attributed to the structural degradation of Makrofol-N on swift ion irradiation.     

Die Eigenschwingungen des Metall-Hydratkomplexes in BeSO4·4H2O und BeSO4·4D2O

Infrared reflection spectra of single crystals of BeSO₄·4H₂O and BeSO₄·4D₂O have been obtained in polarized light at 300°K and at 14°K in the region between 4000 cm^?1 and 300 cm^?1. By a Kronig-Kramers analysis, the frequencies of the infrared active transitions have been calculated. These transitions are attributed to internal vibrations of the water molecules and sulfate ions and, in the region between 1000 cm^?1 and 300 cm^?1, especially to internal and external vibrations of the tetrahedral Be⁺⁺·4aqu-complexes. The vibrational modes of these complexes consist of a superposition of translational and librational modes of the water molecules and translational modes of the central Be⁺⁺-ion. The vibrational frequencies and normal modes of this complex have been calculated in a central-force model, and force-constants have been determined by fitting the calculated frequencies to the observed spectra. The calculations have shown that the modes, which comprise mainly translational motions of the water molecules, are strongly coupled with librational motions of the water molecules. On the other hand, there exist pure librational modes with practically no admixture of translational motions. The optimum sets of force constants for the BeSO₄·4H₂O crystal and the BeSO₄·4D₂O crystal differ in a manner which can be understood under the assumption that the dimensions of the Be(D₂O)₄ complex are about 0.1 Å larger than those of the Be(H₂O)₄ complex. Some arguments supporting this conclusion will be discussed.     

A Co-Crystallised Cobalt(II) Cluster of Pyridinedicarboxylic Acid (PDC) as a Luminescent Material for Selective Sensing of Methanol

A luminescent Cobalt(II) co-crystal [Co₁₃(PDC)₁₆(H₂O)₂₄.7H₂O] 1 (where H₂PDC?=?2,6-pyridinedicarboxylic acid) have been prepared by oven-heating and slow evaporation of solvent. Single crystal X-ray diffraction (SCXRD) analysis revealed that 1 is a mixture of complexes that crystallizes in the triclinic space group P-1 and the geometry around the Co(II) ions is octahedral. The structure is extensively imbued with hydrogen bonding that helps in stabilizing the complex. Thermogravimetric analysis indicates that 1 is thermally stable up to 364 ^οC. The luminescence properties of 1 revealed a strong emission centered at 437 nm (λex?=?345 nm) assigned to ligand to metal charge transfer (LMCT). The luminescence sensing of 1 towards volatile organic molecules were also examined. However, 1 displayed a turn off towards methanol compared to other molecules with high quenching efficiency and low limit of detection (3.5?×?10^?4 vol%). The results show excellent selectively and high sensitivity. Powder X-ray diffraction studies revealed that the structural integrity of the complex was maintained after exposure to methanol vapour. Theoretical studies also revealed small binding energy (?413.2 au) and low energy gap (1.19) for 1-CH₃OH adduct.

     

Infrared intensities of ion-water interactions in aqueous electrolyte solutions

The i.r. absorption intensities have been measured of the fundamental vibrations of water molecules in metal halide aqueous solutions. Pseudo-isosbestic points were observed in the regions of both the stretching and bending vibrations and interpreted in terms of two states of water molecules in the solutions. The intensities of the stretching vibrations of water molecules coordinated to the dissolved ions have been estimated. The intensities become stronger in the order, Li⁺ > Na⁺ > K⁺ for the cations and F^- > Cl^- > Br^- > I^- for the anions. These orders are consistent with the strengths of the ion-water interactions, which are related to the dynamical behavior of the water molecules in the primary hydration shell.