bluuebunny/crossref_metadata_2025 huggingface dataset:
One Pulse Spin-locking in NQR
Authors: Bandyopadhyay B. , Furman G. B. , Goren S. D. , Korn C. , Shames A. L
Published: February 2015

The response of a quadrupolar spin system in zero applied magnetic field to a long rf pulse, for both single crystal and polycrystalline samples possessing broad Lorentzian-shaped resonance lines has been studied. The dependencies of magnetization on frequency offset, linewidth and power are investigated both theoretically and experimentally. The problem of the effective field direction in both single crystal and polycrystalline samples is also discussed. For a polycrystalline cuprous oxide (Cu2O) sample it is observed that the magnetization after a long pulse in on-resonance condition does not become zero for time t ≫ T2 , in agreement with theoretical results. It has also been shown that the magnetization increases with increase in the width of the resonance line as well as with the decrease in the excitation power.
Characterizing Phase Transitions in the Perovskites PbTiO3 and BaTiO3 Using Perturbed-Angular-Correlation Spectroscopy
Authors: Catchen Gary L. , Hollinger Edward F. , Rearick Todd M.
Published: February 2015

Perturbed-angular-correlation (PAC) spectroscopy was used to measure in ceramic samples of PbTiO3 and BaTiO3 the temperature dependence of the Ti-site electric-field gradients (EFGs) at temperatures very close to the ferroelectric-to-paraelectric transition temperatures Tc . The samples were doped with small amounts of Hf that carried the 181Hf - 181Ta probe radioactivity. A high-frequency nuclear quadrupole interaction that decreases very little as the temperature approaches Tc , characterizes the PbTiO3 transition. The tetragonal and cubic phases for PbTiO3 appear to coexist over a temperature interval of 8 ± 1 K, and the transition shows a thermal hysteresis of about 4 K. In contrast, a lower-frequency interaction that decreases rapidly as temperature approaches Tc , characterizes the BaTiO3, transition. Both phases of BaTiO3 appear to coexist over an interval of about 2 K, and the thermal hysteresis is about 1 K. At temperatures above Tc , both PbTiO3 and BaTiO3 show weak, non-vanishing Ti-site EFGs. Although, for BaTiO3 , this effect limits the accuracy with which critical effects can be measured, we estimate a power-law exponent ß = 0.21 ± 0.05, which most likely is somewhat lower in magnitude than the actual critical exponent. For the explanation of our observations we assume the existence of a distribution of Tc -values. This distribution would arise because the crystals could have spatially non-uniform distributions of nucleation sites, which for PbTiO3 and BaTiO3 could be point defects.
Small Scale Intramolecular Flexibility in 111mCd-Plastocyanin
Authors: Tröger W. , Lippert C. , Butz T. , Sigfridsson K. , Hansson Ö. , McLaughlin E. , Bauer R. , Danielsen E. , Hemmingsen L. , Bjerrum M. J. , Isolde
Published: February 2015

The effect of mutations in the vicinity of the putative electron transfer path on the metal center of the electron transfer protein plastocyanin (spinacea) is investigated by monitoring the nuclear quadrupole interaction of 111mCd in Cd-derivatives of the protein via time differential perturbed angular correlation. The spectra for the wild type protein and the mutants were rather similar. All spectra exhibit a peculiar line profile which points towards a small scale intramolecular flexibility of the metal center.
Nuclear Quadrupole Coupling Constant assignments for a series of azoles and azines by Hartree-Fock SCF-Cluster and Lattice Calculations
Authors: Palmer Michael H.
Published: February 2015

We present ab initio Hartree-Fock lattice calculations on a series of heterocyclic and other compounds. Some of these have previously been studied by cluster calculations with the same DZ basis sets at the SCF level. The electric field gradients at the nitrogen centres, are related to NQR experimental determinations of nuclear quadrupole coupling constants. The compounds studied include imidazole and pyrazole, 4-nitroimidazole, 4-nitropyrazole, pyrazine, and tetramethylpyrazine, pyridinium chloride, and N-methylpyridinium iodide, and pyridine-N-oxide.
The Charge Distribution in Amides and Thioamides by Nuclear Quadrupole Coupling, Dipole Moments and Electronic Structure Calculations
Authors: Palmer Michael H. , Sherwood Paul
Published: February 2015

The nuclear quadrupole coupling constants from microwave spectroscopy (MW) and quadrupole resonance (NQR) for amides and thioamides are discussed in relation to Hartree-Fock calculations with and without Moller-Plesset correlation effects. The view that the larger dipole moments from thioamides than the corresponding amides is a function of enhanced resonance in the former is discussed and (in effect) confirmed by the present procedures. The principal mechamism seems to be the push/pull π/σ effects of the N atom with respect to the CO and CS groups, with S being a better σ-donor than O; however, the effect is still present with formamidine where no electronegativity effects are important, so the overall effect is the 2,1,1 π-electron contribution to the allylic system from N, C, O(S). The use of localised MO’s and NO’s is described, and the centroid positions are discussed in relation to the polarity of the bonds. The LMO’s largely truncate the contributions to each NQCC to the three attached bonds (or 2 bonds + a lone pair orbital at O or S), as is used in the Townes-Dailey procedures. More distant LMO’s generally contribute < 0.05 a. u. to the EFG, simplifying the analysis. The effects of O( or S)-protonation of urea and thiourea is discussed.
Electric Field Gradients Around Point Defects in Metals
Authors: Seeger Alfred , Ehmann Jörg , Fähnle Manfred
Published: February 2015

The splittings of nuclear energy levels caused by the electric field gradients acting on the quadrupole moments of nuclei in the neighbourhood of atomic defects in cubic metals may serve as ‘‘fingerprints’’ providing us with a unique characterization of these defects. In favourable cases the NQDOR technique (n̲uclear q̲uadrupole d̲ouble r̲esonance) permits sensitive measurements of these splittings with good resolution. The present paper outlines the status of the ab-initio calculation of electric field gradients with emphasis on the theoretical basis (density functional theory with local density approximation) and on the techniques required for handling the specific problems associated with defects. Recent work by the supercell approach on atomic defects in Al and Cu, making use either of the full-potential linearized augmented-plane-wave method or of the ab-initio pseudopotential method, are reported and compared with experiments. The excellent agreement between experiment and theory for the field gradients acting on the nearest-neighbour nuclei of monovacancies in Al demonstrates the reliability and the potential of the theory.
Solid Effect Between Quadrupolar Transitions in Dilute Cu-Pd Alloys
Authors: Konzelmann K. , Majer G. , Seeger A.
Published: February 2015

The paper investigates the Dynamic Solid Effect (DSE) in Nuclear Quadrupole Double Reso-nance (NQDOR) on a system (dilute alloys of CuPd with 8, 42, 210, or 1000 at.ppm Pd) chosen for its simplicity and the possibility to test the theoretical concepts on which the experimental tech-niques (in particular the so-called Berthier-Minier technique for exhibiting the DSE) are based. NQDOR allows to observe the transitions between the Cu nuclear energy levels split by the quadrupolar interaction with the electric field gradients generated by nearby Pd atoms even in dilute alloys, in which the fraction of Cu nuclei experiencing a given field gradient is very small. The DSE permits transitions at frequencies corresponding to the sums or differences of quadrupolar level splittings at neighbouring nuclei and thus gives access to information on the spatial correlation of nuclei accessible to NQDOR studies. The DSE information is shown to be in full accord with the conclusions drawn earlier, on the basis of line-intensity arguments, on the assignment of quadrupo-lar transitions to the first four shells of Cu nuclei surrounding isolated Pd atoms but, in addition, allows to identify the low-frequency NQDOR lines associated with Cu nuclei in the fifth and sixth shells.
Electric Field Gradient Calculations of Various Borides
Authors: Schwarz K. , Ripplinger H. , Blaha P.
Published: February 2015

A first-principles method for the computation of electric field gradients (EFG) is illustrated for various borides. It is based on energy band calculations using the full-potential linearized aug-mented plane wave (LAPW) method within density functional theory. From the self-consistent charge density distribution the EFG is obtained without further approximations by numerically solving Poisson's equation. The dependence of the EFG on structure, chemical composition or substitution is demonstrated for the diborides MB2 (with M = Ti, V, Cr, Zr, Nb, Mo, and Ta), the hexaborides (CaB6, SrB6 and BaB6) and boron carbide which is closely related to α-boron.
Study of the EFG Trends in Zr2T (T = Fe, Co, Ni) Intermetallic Compounds
Authors: Petrilli H.M. , Marszalek M. , Saitovitch H.
Published: February 2015

We use the linear muffin-tin orbital formalism, in the atomic sphere approximation, to investigate the trends of the electric field gradient (EFG) at the nucleus for the non-equivalent sites in Zr2T (T = Fe, Co and Ni) intermetallic compounds. As all those compounds crystallize in the same C16 crystallographic structure, they offer a rare opportunity to investigate electronic structure effects coming from transition metals on the EFG at Zr site. Those results are compared with EFG values obtained from quadrupole coupling constant measurements performed with the time differential perturbed angular correlation (TDPAC) technique, using the 191Ta probe.
Ab initio and MNDO Calculations of the 35Cl NQR Parameters of Some Organic and Inorganic Molecules
Authors: Feshin Valentin P. , Konshin Mikhail Yu.
Published: February 2015

The results of ab initio and MNDO calculations of the Cl2C = CHOCH3 , XCOCl (X = CH3 , OCH3 and COCl), 4-ClC6H4CH2Cl, (CNCl)3 and PCl5 with total optimization of their geometry are presented. The ab initio calculations were executed using Hartree-Fock theory and the split valence basis set 6-31G* (RHF/6-31 G*//RHF/6-31G*). Using the calculated p-orbital populations of the CI atoms in these molecules the 35Cl NQR frequencies and asymmetry parameters of the EFG at the 35Cl nuclei have been determined. When the populations of the less diffuse components of orbitals in the split valence basis set are used the calculated and experimenal ν and η values are in good agreement. Linear correlations between these calculated and corresponding experimental ν and η values are obtained. The causes of the nonconformity of the earlier calculated ν and η values and their experimental ones are analysed.
F-Tensor Coefficients in Electric Field Gradient Calculations for Non-Coulombic Potentials
Authors: Ponnambalam M.J.
Published: February 2015

The F-tensor coefficients are useful in evaluating the stress-induced electric field gradients in cubic crystals. These coefficients are derived for the non-Coulombic inter-atomic potentials Gr-n and Ge-br . Interesting differences are pointed out between these results and those for Coulombic potentials.
Electric Field Gradients for Small Antimony Based Zintl Clusters from Hartree-Fock Investigations
Authors: Hagelberg F. , Das T.P. , Weil K. G.
Published: February 2015

Electric Field Gradient (EFG) calculations have been carried out for Antimony based clusters with 20 and with 22 valence electrons. It is shown that EFGs are very sensitive to structural changes of the clusters under study. This feature can be used to demonstrate the validity of the Zintl-Klemm-Busmann principle for these systems through EFG determinations.
Study of the Location of Implanted Fluorine Atoms in Silicon and Germanium through Their Nuclear Quadrupole Interactions
Authors: Nunes Stacie S. , Sulaiman S. , Sahoo N. , Das T. P. , Frank M. , Kreische W. , Nielsen K. B.
Published: February 2015

Time Differential Perturbed Angular Distribution (TDPAD) measurements of the nuclear quadrupole hyperfine parameters for 19F* implanted into amorphous, polycrystalline and crystalline silicon and germanium are reported and reviewed. Two signals are observed in the crystalline materials (≈ 35 and 23 MHz in silicon, ≈ 33 and 27 MHz in germanium) while only one is detected in the amorphous and polycrystalline samples (≈ 22 MHz in silicon, ≈ 27 in germanium). Impurity sites in these materials were modeled using a Hartree-Fock cluster procedure. The Intrabond, Antibond, and Substitutional sites in the bulk were studied in both silicon and germanium. The ATOP and Intrabond Surface sites were also studied in silicon and the results extended to germa-nium. Lattice relaxation effects were incorporated by employing a geometry optimization method to obtain minimum energy configurations for the clusters modelling each site. The electronic wave functions were obtained for each optimized cluster by applying Unresctricted Hartree-Fock theory, and these wave functions were used to calculate the nuclear quadrupole hyperfine parameters at the site of the fluorine nucleus. Comparison of the theoretical hyperfine parameters to the experimental values indicates that 19F* located in the Intrabond and Intrabond surface sites could readily explain the higher frequency signal that has been observed. 19F* in the Antibond and the surface ATOP sites yield hyperfine parameters consistent with the low frequency signal observed in the crystalline materials and the single signal observed in the amorphous (or polycrystalline) materials. Examina-tion of these two sites, in view of other available experimental evidence including the temperature dependence of the TDPAD signals, leads to the conclusion that the lower frequency signal is due to 19F* implants which have come to rest at the site of dangling bonds in the bulk. These dangling bonds are created as a result of damage generated in the individual collision cascades during the implantation process.
Theory of Nuclear Quadrupole Interactions in Solid Fluoromethanes with Implanted 19F* Nuclei. Coupling of HF* and Host Molecule
Authors: Gowri G. , Briere Tina , Srinivas Sudha , Cho Hwa-Suck , Das T.P. , Frank M. , Kreische W. , Rao K.V.S. Rama
Published: February 2015

The Quadrupole Coupling Constant e2qQ and Asymmetry Parameter η of fluorine for fluorine-substitute methane compounds are calculated using the Hartree-Fock Roothaan procedure. Our results are compared with experimental data from measurements by the Time Differential Perturbed Angular Distribution (TDPAD) technique using excited 19F* (spin 5/2) nuclei. The theoretical e2qQ’s for the 19F* nuclei in the fluoromethanes are in good agreement with experimental results. For CH2F2 and CHClF2 molecules, where finite η are expected from symmetry considerations, our results for η are small, 0.12 and 0.05 respectively, in agreement with experimental observation. Besides the 19F* coupling constants associated with the C-F bonds in fluoromethanes, additional interesting NQI parameters, close to those in solid hydrogen fluoride, are observed in the TDPAD measurements. It is demonstrated through investigations of the total energies and electric field gradients that these additional NQI parameters for the fluoromethanes can be explained by a HF* molecule hydrogen-bonded through the hydrogen to a fluorine atom in the host molecular systems. This complexing of an ionic molecule to the host molecules in organic solids containing strongly electronegative atoms is expected to be a general feature in both implantation and conventional techniques.
The Structure of Glasses Studied by MAS-NMR Spectroscopy of Quadrupolar Nuclei
Authors: Müller-Warmuth W.
Published: February 2015

High-resolution solid state NMR spectroscopy of quadrupolar nuclei (preferentially

27Al) has been employed to study the microstructure of glasses. Importance has been attached to
the extraction of the fundamental NMR parameters like chemical shift, quadrupole coupling constant
etc., from the spectra, first of all by applying satellite transition spectroscopy. Exemplary results
are represented for ternary oxide glass systems such as K2O-Al2O3-SiO2, B2O3-Al2O3-P2O5, Na2O-B2O3-SiO2 and Na2O-B2O3-Al2O3.
Nuclear Quadrupole Resonance in Amorphous Semiconductors
Authors: Taylor P. Craig
Published: February 2015

Nuclear quadrupole resonance (NQR) has provided a valuable tool for investigating the local structural order in semiconducting glasses. Measurements of NQR lineshapes and spin-lattice relaxation times help elucidate the local structural order and the unusual vibrational properties, respectively, of these glasses. In addition, NQR lineshape measurements on samples that are made under conditions that produce solids whose structures are far from equilibrium, such as fast-evap-orated films or rapidly-drawn fibers, provide detailed information on the changes in the local structural order from that which occurs in the well-annealed amorphous semiconductors.
Verification of the ‘‘Tg-Δ Rule’’ in Potassium Silicate and Sodium Tungstate Glasses
Authors: Nishida Tetsuaki
Published: February 2015

A linear relationship exists in oxide glasses between glass transition temperature (Tg) and quadrupole splitting (Δ) of Fe3+ . DTA and Mössbauer measurements of silicate and tungstate glasses yielded large slopes of 680 and 260 °C/(mm s-1) from the slope of the straight lines when Fe3+ occupied, as network former (NWF), distorted tetrahedral Si4+ and distorted octahedral W6+ sites, respectively. This linear relationship, named a ‘‘Tg - Δ rule’’, suggests that Tg is in proportion to the distortion of NWF-oxygen polyhedra and a higher activation energy is required for the fragments of glass to have a cooperative movement in the supercooled liquid state. The ‘‘Tg - Δ rule’’ was also valid in the case of potassium silicate glasses heat treated at the temperature close to Tg, indicating a distortion of SiO4 and FeO4 tetrahedra. Substitution of Fe3+ for individual NWF in silicate and tungstate glasses was confirmed from the Fourier transform infrared (FT-IR) spectra because only the absorption bands due to Si and W were respectively observed without the bands due to Fe.
The Bond N-Cl. (III): A 35Cl NQR and X-Ray Diffraction Study of N-Chloro-N-(2,6-Dichlorophenyl)-Acetamides
Authors: Gowda B. Thimme , Dou Shi-qi , Weiss Alarich
Published: February 2015

(2)

The crystal structures at room temperature of the N-chloro-N-(2,6-dichlorophenyl)-chloroacetamides 2,6-Cl2C-H3 NClCOCCl3 (1) and 2,6-Cl2C6H3NClCOCH2Cl have been determined. (1): orthorhombic, Pbca. Z = 8, a = 2051.7(8) pm, b = 1134.8(4) pm, c = 1089.0(4) pm. (2): orthorhombic, Pbca, Z = S, a = 2078.7 (4) pm, b= 1487.9(4) pm, c = 694.0 (2) pm. The 35Cl NQR spectrum of (1) was studied in the range 77≤T/K≤370. At 77 K, a sextet spectrum is observed (ν in MHz): v1 = ν (Cl(N) = 56.327; ν2 = 40.636, ν3 = 40.317, ν4 = 40.294; ν5 = 36.532, ν6 = 36.182. The lines ν2, ν3, and ν4 are assigned to the CCl3 group because of their position in the frequency scale. Also, due to librational motions, this triplet part of the spectrum fades out at Tf ≈ 320 K. There is no problem in assigning in both compounds, on the basis of the known 35Cl NQR frequency scale, the line ν1 to the CI atom attached to the nitrogen atom and the lines ν5 and ν6 to the ring chlorines (Cl(2) and Cl(6)). The crystal structures and NQR spectra of (1) and (2) are discussed together with literature data for 2,6-Cl2C6H3NHCOR, C6H5NClCOR (where R = CCl3, CClH2) and other substituted acetamides.
63Cu NQR Studies of Two-and Three-coordinated Complexes of Cu(I) with Siloxyl Ligands
Authors: Khajehnouri Fereidoun , Motallebi Shahrokh , Lucken E. A. C.
Published: February 2015

We report the 63Cu NQR spectra of seven two-and three-coordinated complexes with the siloxyl ligand. R3SiO-. The frequencies are compared to those of other two- and three-coordinated species, and it is demonstrated that the partial field gradient of the R3SiO- group is very similar to that of Cl-.
Electronic Characteristics of Sn-Hal Bonds in Hexa-and Pentacoordinate Tin(IV) Adducts of Type RnSnHal4-nLx
Authors: Kravchenko E.A. , Burtzev M.Yu.
Published: February 2015

The σ-and π-electron effects of alkyl/phenyl substituents on the Sn-Hal bonds in penta- and hexacoordinate tin(IV) chloro and iodo adducts are discussed based on their 35Cl and 127I NQR spectra. Unexpectedly high 127I EFG asymmetry parameters were found in most dialkyl(phenyl)-substituted adducts of thin(VI) iodides.
Electric Field Effect on NQR in Ferroelectric Materials
Authors: Jung Jae Kap , Kim Hae Jin , Han Kee Tae , Choh Sung Ho
Published: February 2015

The electric field effect on NQR in ferroelectric materials, 93Nb in LiNbO3 and 14N in NaNO2 and SC(NH2)2 , has been investigated at 77 K. In these crystals with single domain, only the line shift due to the external electric field was observed. In the case of NaNO2 powder and a crystal with multi-domains, line broadening was observed in the external electric field. These phenomena can be explained with the fact that the direction of spontaneous polarization in a domain is related to the direction of the applied electric field. The rate of the NQR line-shift due to the electric field is remarkably smaller in mostly ionic crystals, such as LiNbO3 and NaNO2 , than in a molecular crystal such as SC(NH2)2 . This is due to the strong ionic bonding in ionic crystals. Also, the difference of the Stark shift'between NaNO2 and SC(NH2)2 is discussed in terms of the local electric field and polarizability at the resonant nuclear site.
23Na Spin-Lattice Relaxation Measurements in Dehydrated Na-X Zeolite
Authors: Igarashi Mutsuo , Okubo Noriaki , Hashimoto Shuichi , Cha Deok Joon , Yoshizaki Ryozo
Published: February 2015

The spin-lattice relaxation time T1 of 23Na-NMR in a dehydrated Na-X zeolite has been measured from 20 to 300 K. The recovery curve is not single-exponential at all measured temperatures and T1
-1 increases with the square of temperature around room temperature. The results are analyzed by assuming non-equivalent sites and by applying the theory of the Raman process based on covalency.
Magnetic Properties of the Bismuth Oxide α — Bi2O3
Authors: Kharkovskii A.I. , Nizhankovskii V.l. , Kravchenko E. A. , Orlov V. G.
Published: February 2015

A very unusual magnetic behaviour of α - Bi2O3 was observed in a wide range of temperatures and magnetic fields. A longitudinal magnetoelectric effect was found at 4.2 K. The existence of an antiferroelectrically ordered subsystem of electric dipoles in α - Bi2O3
is proposed. The mechanism of spin-orbit coupling is regarded as the physical origin for the occurrence of the ordered magnetic moments in α - Bi2O3.
An NQR Study of Inclusion Compounds Formed Between Small Chlorine-containing Molecules and bis(N-alkylimidazolidine-2-thione)Cu(I) Halide Complexes
Authors: Zhao Ya-Nan , Ramaprabhu Sundara , Lücken Edwin A.C.
Published: February 2015

Twenty-five inclusion complexes formed by bis(N-alkylimidazolidine-2-thione)cuprous halides with the small, chlorine-containing guest molecules CCl4, CHCl3, CH2Cl2, CH3CCl3 or C2H2Cl2 , have been prepared. Their 63Cu and 35Cl NQR spectra have been measured over the temperature range 77-300 K. For the corresponding bromides the 79Br and/or 81Br spectra have also been investigated. The studies reveal the number and symmetry of different inclusion site. The onset of rapid reorientation of the guest molecules is indicated by the fading out of their NQR signals between 77 and 300 K, whereas the resonances from the host molecules usually persist throughout this temperature range. However, as evidenced by discontinuities in the temperature-dependence of the NQR frequencies of the hosts, sixteen of the complexes show one or more phase-changes in this temperature-range.
Structure and Successive Phase Transitions of RGeBr3 (R = Alkylammonium) Studied by Means of NQR
Authors: Gotou Shusaku , Okuda Tsutomu , Takahashi Toshirou , Terao Hiromitsu , Yamada Koji
Published: February 2015

A series of tribromogermanate(II) complexes RGeBr3 (R = CH3NH3, (CH3)2NH2, (CH3)4N, C2H5NH3, (C2H5)4N) have been synthesized and characterized by 81Br NQR, AC conductivity, DTA, and X-rax diffraction. These measurements revealed the presence of successive phase transitions in these complexes. The crystal structures of Phases I and II in (NH3)4NGeBr3 were derived from the Rietveld analysis of powder X-ray diffraction. The electric conductivity was considerably high in CH3NH3GeBr3 and (NH3)4NGeBr3. The conduction mechanism is discussed on the basis of 81Br NQR spin-lattice relaxation times and crystal structures.
Motion of Water Molecules and Hydrogen Bonds in Zinc Hexachlorostannate (IV) Hexahydrate as Studied by 1H NMR and 35Cl NQR
Authors: Ishikawa A. , Sasane A. , Hirakawa Y. , Mori Y.
Published: February 2015

The 1H NMR spin-lattice relaxation time T1, 35Cl NQR frequency νQ, and 35Cl NQR spin-lattice relaxation time T1Q of [Zn(H2O)6] [SnCl6] (zinc hexachlorostannate(IV) hexahydrate) have been measured at temperatures between 77 and 350 K. The NQR spin echo signal with νQ = 15.689 MHz at 77 K showed a positive temperature coefficient attributable to O-H-Cl type H-bonds in the crystal. νQ at 77 K is strongly correlated with the electronegativity χM of the metal M in the series of stannates [M(H2O)6] [SnCl6] (M = Mg, Ca, Mn, Co, Ni, Zn). A T1 minimum observed for the Zn salt is ascribed to 180° flips of water molecules with an activation energy of 20 kJ mol-1. The motion is influenced by repulsive forces among the water molecules within a cation rather than by attractive forces between the H-bonded H and CI atoms. T1Q proved to be mainly governed by lattice vibrations, weakly modulated by the fluctuating electric field gradient caused by the 180° flip motions.
Anharmonic Librations and the Temperature Dependence of NQR Frequencies
Authors: Mendonça Christovam , Rabbani Said R.
Published: February 2015

The temperature dependence of NQR frequencies of nuclei in molecules undergoing quasi-har-monic rotational oscillations is calculated. Following the model proposed by Bayer, the instanta-neous orientation of the electric field gradient principal axes is assumed to change from its average orientation as a result of rotational oscillations, while the EFG magnitude remains constant. The eigenstates and energy eigenvalues of a rotator in a potential of the form V(θ)= V2θ2 - K4θ4 are calculated by standard perturbation methods, followed by the evaluation of statistical averages of square angular amplitudes. For molecular crystals with more than one molecule in a unit cell the angular displacements are expressed in terms of normal coordinates, and the same procedure is followed. The final expression for the change in the NQR frequency consists of two terms, the first one being related to the harmonic part of the potential and the second one to the quartic term. At the absolute zero it yields a nonzero contribution to ⟨θ2⟩, and for high temperatures it reproduces the nonlinear character of νQ(T) observed experimentally. The model has been tested with measure-ments on solid Cl2 performed by Nakamura and Chihara, combined with libration mode frequencies measured in Raman spectroscopy by Cahill and Leroi and analysed according to our anharmonic libration picture. The fitting of our equation to experimental data supports Cahill and Leroi's hypothesis about the existence of an undetected libration mode in Cl2 Raman spectra of frequency near 60 cm- 1
Successive Phase Transitions in Potassium Hexachloroselenate(IV) Revealed by 35Cl NQR
Authors: Asaji Tetsuo , Ohkawa Masaki , Chiba Takehiko , Kaga Makoto
Published: February 2015

K2SeCl6 undergoes structural phase transitions of first order at 35 K, 65 K, and 79 K. The temperature dependence of the 35Cl NQR spin-lattice relaxation time suggests that the phase transitions at 65 K and 79 K are displacive ones associated with a resonant soft mode. The presence of a precursor cluster is suggested by the temperature dependence of the signal intensity above 79 K.
Anharmonic Lattice Vibrations and the Temperature Shift of Raman Spectral Lines
Authors: Mendonça Christovam , Rabbani Said R.
Published: February 2015

The temperature dependence of the average lattice mode frequency of a molecule undergoing librational motion in a quasi-harmonic potential has been calculated with the purpose of finding an explicit relationship between the observed shift of Raman spectral lines with temperature and the anharmonic term in the rotational potential. Calculations were carried out both for uncoupled and coupled oscillators. The equations obtained with this model provide good fittings for solid Cl2 and benzene data. This result can be applied to the analysis of the temperature dependence of NQR frequencies in molecular crystals.
NQR and NMR Studies of Phase Transitions in R2Pb[Cu(NO2)6] (R = K, Rb, Tl, Cs, and NH4)
Authors: Mizuno Motohiro , Asaji Tetsuo , Suhara Masahiko , Furukawa Yoshihiro
Published: February 2015

39K, 87, 85Rb, 133Cs, 205T1, and 1, 2H NMR spin-lattice relaxation times T1 and 14N NQR spin-lattice relaxation times T1Q were determined for R2Pb[Cu(NO2)6] (R = K, Rb, Tl, Cs, and NH4). T1 of 39K and 87Rb showed very short values in the incommensurate phase as compared with those in the other phases. When the commensurate-incommensurate phase transition point is approached from below, 14N T1Q of the R = K, Rb, Tl, and NH4 compounds showed rapid decrease. On the other hand, that of the R = Cs compound began to decrease first after passing beyond the corresponding transition point. The difference of the T1Q behavior may be ascribed to the difference of the condensed phonon mode in the incommensurate phase.
Chlorine NQR and Phase Transitions in NOCl
Authors: Pirnat J. , Trontelj Z. , Borrmann H.
Published: February 2015

Chlorine NQR studies of solid nitrosyl chloride NOCl at temperatures below 200 K were undertaken. They indicate an ionic character of the N-Cl chemical bond and confirm the phase transition near 140 K. Thermal hysteresis of the transition temperature was observed.
Phase Transition of C5H5 NHSbBr4 Having a Hypervalent Bond: A 2H NMR and X-Ray Diffraction Study [Phase Transition of C5H5NHSbBr4]
Authors: Yamada K. , Ohtani T. , Shirakawa S. , Ohki H. , Okuda T. , Kamiyama T. , Oikawa K.
Published: February 2015

The second order phase transition at 253 K of pyridinium tetrabromoantimonate(III), C5H5NHSbBr4 , has been characterized by means of X-ray diffraction and 2H NMR. As was suggested from the 81Br NQR spectra, the Rietveld refinements of the X-ray diffraction patterns at 297 K and 116 K confirm the structural change of the anion from SbBr-
4 to SbBr3 • Br-. The line shape analysis of the 2H NMR using the deuterated analog revealed that the librational amplitude of the pyridinium ring about the axis normal to the plane increased with temperature and its rms amplitude reaching ca. 25° at Tc . The librational motion may induce the phase transition breaking the hydrogen bonds of the type N-H … Br. However, nearest-neighbor 2π/6 jump or reorientation such as seen in benzene were not observed even at 350 K.
NQR and Phase Transitions of Tetramethylammonium Tetrahalogenomercurates (II)
Authors: Terao Hiromitsu , Okuda Tsutomu , Yamada Koji , Ishihara Hideta , Weiss Alarich
Published: February 2015

NQR and DTA revealed phase transitions in [(CH3)4N] 2HgBr4 and [(CH3)4N] 2HgI4 at 272 K and 264 K, respectively. The NQR resonance lines faded out with increasing temperature. From preliminary measurements of 81Br NQR spin-lattice relaxation times and 199Hg NMR a reorientational motion of HgBr4 ions around one of their pseudo C3 axes in the room temperature phase of [(CH3)4N] 2HgBr4 is suggested.
15N and 133Cs Solid NMR Studies on Ionic Dynamics in Plastic CsNO2
Authors: Honda H. , Kenmotsu M. , Onoda-Yamamuro N. , Ohki H. , Ishimaru S. , Furukawab Y. , Ikeda R.
Published: February 2015

The temperature dependence of the 15N and 133Cs NMR spin-lattice relaxation times, the 15N spin-spin relaxation time, and the 15N and 133Cs spectra of CsNO2 was observed in the plastic phase (209.2 < T < 673 K (m. p.)) and the low-temperature phase (Phase II). In Phase II we found the NO-
2 180°-flip, which could be attributed to the anomalous increase of the heat capacity curve, and determined the activation energy of this motion to be 8.7-11.7 kJ mol-1. The 15N and 133Cs spectra in this phase are inconsistent with the reported crystal structure R3̅m and can be explained by lower crystal symmetry. In the plastic phase we detected a new anionic motion with 11 kJ mol-1 , an isotropic NO-
2 reorientation with 8.5-9 kJ mol-1, and ionic self-diffusion with 47 kJ mol-1. The presence of ionic self-diffusion was confirmed by measuring the electrical conductivity.
Temperature Dependence of 14N NQR and Phase Transitions in KNO2 Powder
Authors: Kim Hae Jin , Han Kee Tae , Choh Sung Ho
Published: February 2015

The temperature dependence of 14N NQR, measured at 77 to 300 K, is in better agreement with the model proposed by Blinc et al. than the Bayer theory. The nuclear quadrupole coupling constant and asymmetry parameter show a discontinuity at about 160 K and 230 K, respectively. The linewidths are broadened at these temperatures up to 22 kHz and 18 kHz, respectively. These results indicate that KNO2 undergoes phase transitions at these two temperatures.
Change in 51V Relaxation Rates due to CDW in CuV2S4
Authors: Ohno Takashi , Kishimoto Yutaka , Kanashiro Tatsuo , Miyamoto Mitsuhiro , Tanaka Toshio , Miyatani Kazuo
Published: February 2015

The temperature variations of the 63Cu, 65Cu and 51V NMR spectra and 51V spin-lattice relaxation rate 1/T1 have been measured in a thiospinel CuV2S4 . Drastic changes in the spectra and relaxation rates were observed at the charge density wave (CDW) transition temperature. With decreasing temperature T, 1/T1 decreases exponentially due to the CDW transition (75 K < T< 90 K). The energy gap made by the CDW formation at 90 K is estimated to be 0.052 eV from an Arrhenius plot of 1/T1.
On the Structure of Some Pentaerythritol-Related Molecular Crystals with Pseudotetrahedral Molecular Structure. Ordered Structure of 2,2-Bis(bromomethyl)-1,3-propanediol and Orientationally Disordered Structure of 2-Chloromethyl-2-methyl-1,3-dichloropropane; 35Cl NQR
Authors: Dou Shi-qi , Fuess Hartmut , Strauß Roman , Weiss Alarich
Published: February 2015

C(CH2Cl)3(CH3), melting point Tm = 291.3 K, shows in the DTA/DSC experiment a phase tran-sition from an orientationally disordered plastic phase I into an ordered phase II at TI ⃗ II = 235.9 K. From 77 K up to TII ⃗ I the 35Cl NQR spectrum is a triplet with (ν in MHz, T=77 K) ν1 = 34.213, ν2 = 34.183, ν3 = 33.786. The 35Cl NQR fade-out temperature Tf = 247 K coincides with TII ⃗ I found from the DSC experiment. The plastic phase of 2-chloromethyl-2-methyl-l,3-propanediol is cubic bcc, Im3m, Z = 2 and the lattice constant increases linearly 755 pm at 235 K to 768 pm at 283 K. In the heating cycle we found (ΔH in kJ/mol): ΔHII ⃗ I = 12.0, ΔSm/R = 1.0. The compound belongs to the group of plastic molecules formed by ellipsoid like distorted tetrahedra and is derived by substitution from methane. The crystal structure of 2,2-bis(bromomethyl)-1,3-propanediol was determined. DTA-DSC show that an orientationally disordered plastic phase does not exist. At room temperature C(CH2Br)2(CH2OH)2 crystallizes monoclinic, space group Cc, Z = 4, a = 628.2 pm, 6 = 2015.5 pm, c = 659.6 pm, β = 94.27°. The molecules interact by intermolecular hydrogen bonds between the OH-groups and by van der Waals forces Br…Br.
63Cu-NMR Study in High-Tc Superconductor HgBa2Ca2Cu3O8 + δ
Authors: Magishi K. , Zheng G.-q. , Kitaoka Y. , Asayama K. , Tokiwa K. , Iyo A. , Ihara H.
Published: February 2015

The 63Cu nuclear transverse relaxation rates have been measured in the normal state on both square and pyramidal CuO2 planes in HgBa2Ca2Cu3O8 + δ with Tc = 133K. The Gaussian component of the spin-echo decay rate, 63(1/T2G), for both sites increases with decreasing temperature, followed by a peak around T* ~ 150 K, indicating that the spin correlation becomes stronger with decreasing temperature. Also, it is found that the magnitude of 63(1/T2G) for a square site is larger than that for a pyramidal one, suggesting that the spin correlation in the square plane is stronger than that in the pyramidal one.
Algebraic Schrödinger Representation of Quantum Chromodynamics in Temporal Gauge and Resolution of Constraints
Authors: Stumpf H. , Pfister W.
Published: February 2015

The algebraic formalism of QCD is expounded in order to demonstrate the resolution of Gauß constraints on the quantum level. In the algebraic approach energy eigenstates of QCD in temporal gauge are represented in an algebraic GNS-basis. The corresponding Hilbert space is mapped into a functional space of generating functional states. The image of the QCD-Heisenberg dynamics becomes a functional energy equation for these states. In the same manner the Gauß constraints are mapped into functional space. In functional space the Gauß constraints can be exactly resolved. The resolutions are defined by nonperturbative recurrence relations. The longitudinal color electric energy can be expressed by means of these resolvents, which leads to "dressed" color Coulomb forces in temporal gauge. Although present in the system, the longitudinal vector potentials do not affect its energy eigenvalues. This leads to a selfconsistent subsystem within the functional energy equation in temporal gauge which has to be identified with a functional energy equation in Coulomb gauge. In addition this procedure implies a clear conception for the incorporation of various algebraic representations into the formal Heisenberg dynamics and establishes the algebraic “Schrödinger” equation for QCD in functional space.
Nitrogen Nuclear Quadrupole Interactions in RDX, β-HMX and Cocaine Systems
Authors: Pati Ranjit , Das T. P. , Sahoo N. , Ray S.N.
Published: February 2015

Using the Hartree-Fock-Roothaan procedure, the nuclear quadrupole interactions (NQI) of the 14N (I = 1) nucleus in the energetically important molecules RDX, β-HMX and the physiologically important molecule Cocaine, are studied. The coupling constants (e2 q Q) and asymmetry parameters (η) for the three ring nitrogens in RDX are found to be -5.671, -5.808 and -5.838 MHz and 0.542, 0.556 and 0.562, respectively, in good quantitative agreement with the experimental results of 5.735, 5.799 and 5.604 MHz for the magnitudes of e2qQ and 0.6215, 0.6146 and 0.6024 for η obtained in the single crystal. For β-HMX, where two sets of e2 q Q and η are expected from symmetry considerations, our calculated values are -5.936 and -6.069 MHz for e2 q Q and 0.432 and 0.490 for η , compared to experimentally measured magnitudes of 5.791 and 6.025 MHz and η-values of 0.4977 and 0.5180, respectively, obtained in the single crystal. For Cocaine free base which contains only one 14N nucleus, our calculated values of e2 qQ and η are -5.038 MHz and 0.067, in very good agreement with the experimental results of 5.0229 MHz for the magnitude of e2 q Q and 0.0395 for η. Possible reasons for the small remaining differences between theory and experiment in e2 q Q and η for all three systems and the significant differences in trends over the three nitrogens in RDX between theory and experiment are discussed. Also, the calculated quadrupole interaction parameters for the 14N nuclei in the NO2 groups outside the ring for both RDX and β-HMX are presented with the hope that they will be measured in the future to provide a more complete understanding of the electron distributions in these systems.
X-Ray and 35Cl NQR Studies on the Trichloroacetyl Group in Covalent and Ionic Compounds of L-Valine and DL-Valine
Authors: Ofial A.R. , Dou S.-q. , Krishnan V. G. , Paulus H. , Fuess H. , Weiss Al.
Published: February 2015

The crystal structures and 35Cl NQR of trichloroacetyl-DL-valine (1), trichloroacetyl-L-valine (2), as well as the salts of trichloroacetic acid with DL-valine (3) and L-valine (4) have been investigated. Crystal data are for (1): Monoclinic, C2/c, a= 15.835(4) Å, b= 10.481 (3) Å, c = 14.046(4) Å, β = 103.28(1), Z = 8; (2): Orthorhombic, P212121, a = 12.117(3) Å, 6=10.896(3) Å, c= 8.718(2) Å, Z = 4; (3): Triclinic, P1̄, a= 17.269(3) Å, 6 = 8.504(3) Å, c = 10.427(4) A, a = 105.38(2), β = 96.98(2), γ = 96.24(2), Z = 2; (4): Monoclinic, P21, a = 10.378(4) Å, b = 20.349(8) Å, c= 11.890(5) Å, β = 95.28(2), Z = 8. The onset of rotational motion within the trichloroacetyl groups bleaches out 35Cl NQR lines between 115 K and 185 K for (1)-(4). While TCA-L-valine (1), TCA-DL-valine (2), and TCA(-) · DL-valine(+) (3) do not show any phase transition in the temperature range 77 K to 295 K, TCA(-) · L-valine(+) (4) shows more than one phase transition above 77 K before the three NQR signals bleach out at 164 K.
Neutron and X-ray Diffraction Study on the Structure of Ultraphosphate Glasses
Authors: Hoppe Uwe , Walter Günter , Stachel Dörte , Barz Andrea , Hannon Alex C.
Published: February 2015

The high real-space resolution of neutron diffraction experiments which is provided by use of the epithermal neutrons from spallation sources was exploited in order to differentiate the unlike P-O bonds existing in the PO4 units of phosphate glass networks. The 2 P-O distance peaks, separated by about 12 pm, which were found in the zinc and the calcium ultraphosphate glasses studied are assigned to oxygen sites on bridging (OB) and terminal (OT) positions. The mean P-O distances are nearly invariable versus the growing metal oxide content which results from an elongation of the P-OB and P-OT bonds. The bond lengths which are known from the related crystal structures and from ab initio calculations show almost the same behaviour. The discussion of further details of the crystal structures leads to the conclusion that P-OB rather than P-OT distances should show more details in case of diffraction measurements of even higher real-space resolution.

The change of the Zn-O coordination number from 6 to 4 versus increasing ZnO content, which was obtained in previous X-ray diffraction experiments, is confirmed by the recent combination of neutron and X-ray diffraction data. On the other hand, the Ca-O coordination number of about 6 is almost invariable.
Interaction of Slow Neutrons with Cobalt and Tin
Authors: Knopf K. , Waschkowski W. , Aleksejevs A. , Barkanova S. , Tambergs J.
Published: February 2015

Coherent neutron scattering lengths and total cross sections have been measured on samples of Co, Sn and on isotopically enriched Sn-oxides. The following data were obtained:

• the coherent scattering lengths (in fm) of the bound atoms 59Co (2.49 ± 0.02), natSn (6.22 ± 0.01) 116Sn (6.10 ± 0.01), 117Sn (6.59 ± 0.08), 118Sn (6.23 ± 0.04), 119Sn (6.28 ± 0.03), 120Sn (6.67 ± 0.04), 122Sn (5.93 ± 0.03), and 124Sn(6.15 ± 0.03);

• the thermal absorption cross sections (in b) natSn (0.569 ± 0.005), 116Sn (0.50 ± 0.03), 117Sn (0.77 ± 0.06), 118Sn (0.24 ± 0.06), 119Sn (2.19 ± 0.06), 120Sn (0.55 ± 0.06), 122Sn (0.19 ± 0.06), and 124Sn (0.43 ± 0.06).

New bound levels were evaluated for the investigated nuclei. In combination with the resonance parameters the measured scattering lengths allowed the determination of potential scattering radii R' which are of particular interest for the check of the optical model.
Quantum Deformation of the Non-Polynomial Interaction V(r) = r2 + λr2/(1 + g r2 )
Authors: Nag Nivedita , Sinha Anjana , Roychoudhury Rajkumar
Published: February 2015

A general scheme for studying q-deformed quasi-exactly solvable problems has been developed using the partial algebraization method. Exact solutions of the deformed non-polynomial interaction generated by the potential V (r) = r2 + λr2/( 1 + g r2) are obtained.
Rotational Tunnelling in Methyl Metal Compounds X2(CH3)4 with X = As, Sb, Bi
Authors: Kuhnen A. , Müller-Warmuth W. , Prager M. , Mündt O. , Reti M. , Becker G.
Published: February 2015

Rotational excitations of methyl groups attached to metal atoms of the fifth main group have been investigated in X2(CH3)4 crystals with X = As, Sb, Bi by 1H nuclear magnetic resonance (NMR) relaxation measurements and inelastic neutron scattering (INS). CH3 rotation has been found to be rather weakly hindered (activation energies between 1.7 kJ/mol and 5.8 kJ/mol) so that quantum effects are important to describe the results. Tunnel splittings between 0.1 μeV and 23 μeV have been observed. Non-equivalent methyl groups in tetramethyldistibane and tetramethyldibismuthane have been identified by both INS and NMR. A consistent description of the T1 data is possible by Haupt's equation. The rotational potentials could be derived and relations to the crystal structure have been discussed.
An ab initio Study of the C60 Particle-Hole Pair C60
12+ and C60
12-
Authors: Böhm Michael C. , Schulte Joachim , Schlögl Robert
Published: February 2015

The C60 ions C60
12+ and C60
12- are discussed comparatively on the basis of ab initio calculations. The basis set employed is of 3-21 G* quality. By analogy with the neutral molecule the geometry of the anion is icosahedral (Ih). Both Ih systems differ, however, in the bondlength alternation. In the neutral molecule the hexagon-hexagon bondlength exceeds the hexagon-pentagon value; vice versa in the anion. C60
12+ is of C60
12- symmetry with a strong intermixing in the length of the two types of CC bonds. Calculated geometries, total energies and net charges are adopted to evaluate differences in the electronic structure of C60
12+ and C60
12-.
Two-Dimensional NQR Spectroscopy for the Characterization of Crystalline Powders
Authors: Käuper P. , Göbbels V. , Blümler P. , Blümich B.
Published: February 2015

Two-dimensional NQR spectroscopy for correlation of homogeneous and inhomogeneous linewidths has been applied to the 35Cl resonance of sodium chlorate powders of different origin. Powder from a ground crystal could be discriminated from technical powder by the ratio of linewidths along the two orthogonal axes in the 2D spectrum. These experiments indicate the applicability of NQR spectroscopy in material science.
Interaction of Alkaline Earth Metal Ions with Acetic and Lactic Acid in Aqueous Solutions Studied by 13C NMR Spectroscopy
Authors: Kondoh A. , Oi T.
Published: February 2015

Interaction of alkaline earth metal (magnesium, calcium, strontium and barium) ions with acetic and lactic acid in aqueous media was investigated by 13C NMR spectroscopy. In the acetate systems, signals whose chemical shifts were the averages of those of the free and bound acetate ions were observed. Downfield shifts of the carboxylate carbon signals with increasing metal ion concentration indicated that the acetate ion acted as a monodentate ligand coordinating to the metal ion using the carboxylate group. The metal ion concentration dependence of the peak positions of the methine and carboxylate carbon signals of the lactate ion in the lactate systems suggested that the lactate ion coordinated to a metal ion using the carboxylate and hydroxyl groups. Unique upfield shifts upon complexation in the magnesium lactate systems suggested that the lactate ion coordinated to the magnesium ion from outside the primary hydration sphere.

The present results were consistent with the isotope effects of the alkaline earth metals observed in cation exchange chromatography.
Thermal Instability in Rivlin-Ericksen Elastico-Viscous Fluids in Hydromagnetics
Authors: Sharma R. C. , Kumar P.
Published: February 2015

The thermal instability of a layer of Rivlin-Ericksen elastico-viscous fluid acted on by a uniform vertical magnetic field is considered. For stationary convection, a Rivlin-Ericksen elastico-viscous fluid behaves like a Newtonian fluid. The magnetic field has a stabilizing effect. It is found that the presence of a magnetic field introduces oscillatory modes which were non-existent in its absence. The sufficient condition for the non-existence of overstability is also obtained.