bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dielectric Relaxation of 2-Amino-l-butanol
Authors: Witt U. , Stockhausen M. , Jadżyn J. , Kędziora P. 
Published: February 2015

Abstract
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 Van der Waals Complex
Authors: Stahl W. , Grabow J.-U. 
Published: February 2015

Abstract
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 ΔJ = 2.6886(17) kHz, ΔJK = 8.3761 (52) kHz ΔJK= -8.278(5) kHz, ρJ, =0.65993(72) kHz, and ρK = 6.013(11) kHz. The argon atom is placed 3.55 Å above the ring plane
Testing the Reverse Monte Carlo Method Using Scattering Data from Amorphous Ni2Zr
Authors: Bionducci M. , Buffa F. , Licheri G. , Navarra G. 
Published: February 2015

Abstract
The reverse Monte Carlo simulation has been tested by modelling the partial distribution functions of amorphous Ni2Zr. Three runs of simulation involving experimental data from isotopic substitutions neutron scattering and X-ray anomalous scattering are presented
Molecular Motions in Solid [Sb(CH3)4]PF6. A Combined 11H,9F Nuclear Magnetic Resonance and Quasielastic Neutron Scattering Study
Authors: Burbach Günter , Weiden Norbert , Weiss Alarich 
Published: February 2015

Abstract
The molecular dynamics of tetramethylstibonium hexafluorophosphate, [Sb(CH3)4]PF6, is investigated over a broad temperature range. NMR spin lattice relaxation times T1 and the NMR second moments of the 1H and 19F nuclei were determined in the range 8.6 ≦ T/K ≦ 332.3 for polycrystalline [Sb(CH3)4]PF6. 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 P63mc, 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 19F NMR spin lattice relaxation
Application of the Pseudo-Spin Model to the Lowest-Temperature Phase Transition of the Mixed Crystal (NH4)2(1-x)K2xPb[Cu(NO2)6]
Authors: Windsch Wolfgang , Braeter Horst , Gonzalo Julio A. 
Published: February 2015

Abstract
Mizuno et al. developed a jumping model to explain the nonlinear decrease of the phase transition temperature in the mixed crystals (NH4)2(1-x)K2xPb[Cu(NO2)6] with 0 ≦ x ≦ 1. Their implications and results are compared with model parameters and with the results of calculation within the Ising model with transverse field. It comes out that the assumption of a temperature independent transient time in the jumping model corresponds to the admission of tunneling in the Ising model.
Determination of a High Potential Barrier Hindering Internal Rotation in 2-Methylcyclopentanone and α-Methyl-γ-Butyrolactone by Microwave Fourier Transform Spectroscopy
Authors: Alonso J. L. , Heineking N. , Dreizler H. , Heineking N. , Dreizler H. 
Published: February 2015

Abstract
The microwave spectra of α-methyl-γ-butyrolactone and 2-methylcyclopentanone have been reinvestigated using microwave Fourier transform spectroscopy. A-E splittings due to internal rotation of the methyl group have been observed in the ground and several vibrationally excited states for both molecules. From an internal-axis-method analysis of these splittings, values of the methyl group internal rotation barrier of 2.61 kcal mol-1 for α-methyl-γ-butyrolactone and 2.41 kcal mol-1 for 2-methylcyclopentanone have been obtained.
A Theoretical Study of Monosubstituted Cyclopropenyl System
Authors: Yahya Noha M. , Khalil Salim M. 
Published: February 2015

Abstract
MONDO-Forces calculations have been performed, with complete optimization of geometry on X-cyclopropenyl system (cations, radicals and anions), where X is H, O-, OH, CH3 , CN, NO2 , F and CF3 . All substituents prefer planar structure when substituted on both cations and radicals, while they prefer pyramidal structure in the case of anions except CF3 . The substituents O-, OH and F act as electron releasing, while CHO, NO2 and CF3 act as electron withdrawing when substituted on cyclopropenyl system. CH3 and CN show amphielectronic behaviour. They act as electron releasing on the cations and withdrawing on both radicals and anions depending on electron demand. In the case of cations and radicals, all substituents were found to increase the vicinal bonds and decrease the distal bonds and bond angles to which the substituent is attached. For anions the substitutents show no such regularity because the substituents are out of the three-membered ring plane. All substituents increase the stability of the cyclopropenyl system except CF3 in the case of the cation.
Factor Analysis of Long Range Substituent Effects on C-13 NMR Chemical Shifts and Target Factor Testing of Different Types of Substituent Parameters
Authors: Fadhil Ghazwan F. 
Published: February 2015

Abstract
A factor analysis technique has been used to analyse 186 long range C-13 substituent chemical shift (scs) of 90 compounds of the general formula X - G - Y ; X represents the set of substituents, G is a hydrocarbon skeleton, in some cases unsaturated (phenylene) and in other cases saturated. Y consists of a variety of groups which contain the probe site. The data were taken from the literature. Although they were measured in different laboratories, the solvent was CDCl3 in every case. From the value of the factor indicator function (IND) it was concluded that two factors were significant. The validity of several empirical and theoretical substituent parameters has been investigated by Target testing. Models were constructed for the substituent effect. Results from Target factor testing, model designing and linear regression analysis have shown that Reynolds’ σO
R and σF are the best substituent parameters in reproducing the C-13 substituent chemical shift.
Internal Cation Mobilities in Molten (Li, Ag)NO3 and (K,Ag)NO3 Remeasured by the Klemm Method
Authors: Okada Isao , Ichioka Kazunori 
Published: February 2015

Abstract
Internal mobility ratios bLi/bAg and bK/bAg in molten (Li,Ag)NO3 and (K,Ag)NO3 have been measured by Klemm’s countercurrent electromigration method. From these and available data on the densities and conductivities the internal mobilities have been calculated. The present experiments yielded more accurate data than previous ones using other methods. Over the investigated range of concentration and temperature, bAg is greater than bu or bK. The results are discussed together with earlier ones obtained for (Na, Ag)NO3 .
The Inertial Effect in Rotational Fluorescence Depolarization
Authors: Kawski A. , Bojarski P. , Kubicki A. 
Published: February 2015

Abstract
The influence of the moment of inertia on the rotational fluorescence depolarization is discussed. Based on experimental results obtained for five luminescent compounds: 2,5-diphenyloxazole (PPO), 2,2'-p-phenylene-bis(5-phenyloxazole) (POPOP), p-bis[2-(5-α-naphthyloxazolyl)]-benzene (α-NOPON), 4-dimethylamino-ω-methylsulphonyl-trans-styrene (3a) in n-parafines at low viscosity (from 0.22 x 10-3 Pa • s to 0.993 x 10-3 Pa • s) and diphenylenestilbene (DPS) in different solvents, a semi-empirical equation is proposed, yielding moments of inertia that are only two to five times higher than those estimated from the molecular geometry
Temperature Dependence of N2-Relaxation of Rotational Lines of Propionitrile
Authors: Nicolaisen H.-W. , Mäder H. , Rohart F. 
Published: February 2015

Abstract
The temperature dependence of the rotational relaxation of propionitrile, CH3CH2C15N, has been investigated by means of microwave transient emission signals. From analysis of the pressure dependence of the coherence decay rates for the rotational lines (J, K-, K+) = (2, 0, 2)-(3, 0, 3), (2,1, 2)-(3, 1, 3), and (2, 2, l)-(3, 2, 2) pressure broadening parameters have been derived for mixtures with nitrogen in the 210-300 K range and for the pure gas at ambient temperatures
NQR and NMR in High Tc Superconductors
Authors: Asayama K. , Kitaoka Y. , Zheng G.-q. 
Published: February 2015

Abstract
Recent NQR and NMR experiments on La2-xSrxCuO4 , YBa2Cu3O7 , Tl2Ba2CuO6+y , and other compounds are reviewed. The antiferromagnetic spin fluctuations decrease in the order of La, Y, T1 compounds. In the normal state the T-dependence of (T1T)-1 is considered to follow the Curie- Weiss law at high temperature and the (Ti 7") = const law at low temperature. The T dependence of 1/T1 below Tc suggests strongly d-wave pairing. Correlations of the NQR frequency of 63Cu and 17O with the antiferromagnetic spin fluctuations and the superconducting transition temperature are discussed.
NQR Studies of the Structure of Glasses and Crystalline Compounds
Authors: Bray P. J. , Lee DongHoon , Mao De Gen , Petersen G. L. , Feller S. A. , Bain D. L. , Feil D. A. , Pandikuthira Ponnappa , Nijhawan Sumit 
Published: February 2015

Abstract
Pure nuclear quadrupole resonance (NQR) spectroscopy at low frequencies (down to 275 kHz) has been used to investigate a number of borate, aluminate, and vanadate crystalline compounds and borate glasses. The values of the quadrupole coupling constants (Qcc) and asymmetry parameters (η) are obtained with error limits that are one or two orders of magnitude less than those for values obtained from NMR spectra. New sites, not resolved in NMR spectra, have been detected for boron in borate glasses.
14N Quadrupole Interactions in Nitrogen-Containing Ceramics. Effects on 29Si NMR Line Shapes and Structural Implications
Authors: Olivieri Alejandro 
Published: February 2015

Abstract
Simulations of solid-state 29Si NMR spectra in nitrogen-containing silicon ceramics and glasses are described. The range of SiNxO4-x tetrahedra is covered, with emphasis on the experimental conditions needed to observe the effect of the incompletely averaged 29Si, 14N dipolar coupling. A simple equation is discussed concerning its use in the interpretation of these 29Si spectra, including the computation of 14N quadrupole coupling constants with its absolute sign.
Electric Field Gradient in Aluminium due to Vacancy and Muon
Authors: Ponnambalam M. J. 
Published: February 2015

Abstract
The electric field gradients (EFG) in aluminium due to a monovacancy and the interstitial muon are evaluated. The valence effect EFG qv is calculated using perturbed electron density δn(r)values obtained from density functional theory in an analytic expression which is valid at all distances from the impurity. The size effect EFG qs is evaluated using a new oscillatory form for the near neighbour (nn) displacements. The numerical values of qs are computed using fractional nn displacements available in the literature. For the total EFG good agreement with experiment is obtained without the use of any parameter.
14N NQR in 1,10-Phenanthroline and Dicyano bis(1,10-phenanthroline)iron(III)*
Authors: Murgich Juan , Aray Yosslen , Ospina Rico Edgar , Bonalde Ismardo 
Published: February 2015

Abstract

14N NQR spectra of 1,10-phenanthroline and of dicyano bis(1,10-phenanthroline)iron(lll) were obtained at room temperature. An analysis based on the shifts of the NQR frequencies and in the topology of the charge distribution in a model (pyridine) showed that the complex formation produces a strong decrease in the N valence shell nonbonded maximum and an increase in the bonded density along each of the N - H bond directions. The NQR spectrum showed that the complex formation produces only small changes in the charge distribution of the cyanide groups.
81Br and 127 I NQR Studies of (CH3NH3)2HgBr4 and (CH3NH3)2HgI4
Authors: Terao Hiromitsu , Okuda Tsutomu , Minami Aya , Matsumoto Takashi , Takeda Yoshio 
Published: February 2015

Abstract
The 81Br and 127I NQR frequencies in (CH3NH3 ) 2HgBr4 and (CH3NH3 ) 2HgI4 , respectively, have been recorded from above 77 K to around room temperature. The resonance lines exist in a wide range of frequencies. An unusual temperature dependence of the resonance frequencies has been observed. Small 1H - 2D isotope effects have been observed between (CH3ND3 )2HgBr4 and (CH3NH3 ) 2HgBr4 . Both negative and positive frequency differences between the deuterated and the nondeuterated compound have been observed at 77 K. The relatively large asymmetry parameters in the iodine compound decrease with increasing temperature, indicating the existence of H-bonds. The present results are interpreted qualitatively by considering the effects of H-bonding, N - H • • • X, between the halogen atoms and the CH3NH3 ions which may undergo large molecular motions. It is suggested that not only frequency-lowering but also frequency-rising effects may be produced, depending on the direction of the H-bond, i.e., the angle between the Hg -X bond and the X • • • H bond.
7Li-Solid-State-NMR of [Li(N,N,N',N'-Tetramethylethylenediamine)] CLO4 and [Li (N,N,N', N'-Tetramethylethylenediamine)2] Al(CH3)4
Authors: Pietraß Tanja , Burkert Paul K. , Karsch Hans H. 
Published: February 2015

Abstract
The temperature dependent 7Li-solid-state-NMR spectra of the two compounds [Li(N,N,N',N'- tetramethylethylenediamine)]ClO4 and [Li(N,N,N\N tetramethylethylenediamine)2]Al(CH3)4 are presented. Both compounds were investigated in the temperature range 160 K ≦ T ≦ 360 K. Above room temperature, the spectra for the tetramethylaluminate show the typical line shape for a first-order quadrupolar-disturbed central transition with an axially symmetric asymmetry parameter and a slightly positive temperature dependence of the quadrupole coupling constant. The mean temperature coefficient ά = + 9 • 10-4 K -1 . The quadrupole coupling constant is in the range of 36-39 kHz. In the Temperature range 240 K ≦ T ≦ 275 K the quadrupolar splitting cannot be resolved. Below 240 K the quadrupole coupling constant is about 100 kHz. Contrarily, in the Perchlorate the quadrupole coupling constant is 75 kHz and is temperature independent. With increasing temperature the satellites lower in intensity and the central transition undergoes motional narrowing
63,65Cu and 79 81Br NQR Studies of Thione Complexes of Cu(I) Halides
Authors: Ramaprabhu Sundara , Lücken Edwin A. C. 
Published: February 2015

Abstract

63, 65Cu NQR frequencies, together with their temperature dependence, are reported for several complexes formed between cuprous chloride or bromide and heterocyclic thiones. For bromides the 79,81Br resonances have also been detected. These results indicate that, with one exception, the copper atom is tricoordinated by two sulphur atoms and one halogen. Several of these complexes show phase changes in the range 77-300 K.
Bromine-79 NQR for uncoordinated Br– ions in trans-[CoBr2(en)2][H5O2]Br2
Authors: Sasane A. , Matsuda T. , Honda H. , Mori Y. 
Published: February 2015

Abstract
A single 79Br NQR line showing a frequency of 19.594 MHz at room temperature has been observed in the crystals of trans-[CoBr2(en)2] [ H5O2 ] Br2 and assigned to the Br - ions which are not coordinated to the central Co(III) atom. The electric field gradient (EFG) at the Br - nuclei arises from O-H • • • Br - hydrogen bond formation between the Br - ions and the terminal O - H hydrogen atoms in [ H5O2 ] + ions. The induced EFG is greater for the present bromine complex than that for the isostructural chlorine complex. A point charge model calculation explains well the relative magnitude of the EFG in the two crystals by introducing Sternheimer's antishielding factors for the halogen ions.
35Cl NQR and Structural Studies of Chloroacetanilides C6H3Cl2NHCOCH3-xClx, 1 ≤ x ≤ 3
Authors: Groke Dirk , Dou Shi-Qi , Weiss Alarich 
Published: February 2015

Abstract
The temperature dependence of 35Cl NQR frequencies and the phase transition behaviour of chloroacetanilides (N-[2,6-dichlorophenyl]-2-chloroacetamide, -2,2-dichloroacetamide, -2,2,2-trichloroacetamide) were investigated. The crystal structure determination of N-[2,6-dichlorophenyl]- 2-chloroacetamide leads to the following: a = 1893.8 pm, b = 1110.7 pm, c = 472.1 pm, space group P212121 = D2
4 with Z = 4 molecules per unit cell. The arrangement of the molecules and their geometry is comparable to the high temperature phase of the acetyl compound N-[2,6-dichlorophenyl]- acetamide. For N-[2,6-diclorophenyl]-2,2,2-trichloroacetamide it was found: a = 1016.6 pm, b = 1194.3 pm, c = 1006.7 pm, ß= 101.79°, space group P21/c = C5
2h, Z = 4. The structure is similar to the low temperature phase of N-[2,6-dichlorophenyl]-acetamide. Parallelism between the temperature dependence of the 35C1 NQR lines of the CCl3 group and the X-ray diffraction results concerning the different behaviour of the chlorine atoms was observed. The structures of the compounds show intermolecular hydrogen bonding of the N - H • • • O - C type. The phenyl group and the HNCO function are nearly planar.
A bleaching out of several 35Cl NQR lines at a temperature far below the melting point of the substances was observed. The different types of chlorine atoms (aromatic, chloromethyl) can be distinguished by their temperature coefficients of the 35Cl NQR frequencies. All the resonances found show normal "Bayer" temperature behaviour.
N-[2,6-dichlorophenyl]-2,2-diehloroacetamide shows several solid phases. One stable low temperature phase and an instable high temperature phase (at room temperature) were observed. The different phases were detected by means of 35Cl NQR spectroscopy and thermal analysis
Electric Field Effect on 14N NQR in Ferroelectric Thiourea Single Crystals
Authors: Kim Hae Jin , Han, Kee Tae , Choh Sung Ho 
Published: February 2015

Abstract
The electric field effect on 14N NQR in ferroelectric thiourea [SC(NH2)2] single crystals has been investigated at 77 K up to a field of 10 kV/cm. The measured Stark shifts are, in units of kHz • cm/ kV, dv1
+ / dE + = 0.87±0.10, dv1
+dE_ = 1.17±0.20, dv2
+/dE+ = 0.80±0.10, and dv2
+/dE_ = 0.90 ±0.15. These values are on the order of 102 times those found in other ferroelectric crystals such as sodium nitrite (NaNO2 ) . The remarkable difference between these two Stark shifts is discussed by taking into account the polarizability and the local electric field at the 14N sites in these crystals
Reorientational Motion of Trihalogenomethyl Groups in Organic Compounds as Studied by 35Cl NQR and 19F NMR Spectroscopy
Authors: Wigand Silvia , Asaji Tetsuo , Nakamurac Daiyu 
Published: February 2015

Abstract
Trihalogenomethyl derivatives of 4-chloroacetanilide, 4-ClC6H4NHCOCCl3,4-ClC6H4NHCOCF2Cl, and 4 - ClC6H4NHCOCF3 were prepared. The 35Cl NQR and 79FNMR spin-lattice relaxation times T1Q and T1F, respectively, of these compounds were measured at various temperatures. On heating, T1Q of the CCl3 and CF2Cl groups decreased rapidly above ca. 110 and 150 K, respectively, showing the onset of reorientation of the trihalogenomethyl group about the pseudo-triad axis. The activation energies were determined to be 27 and 13 k J mol-1 for the CCl3 and CF2Cl reorientation, respectively. The temperature dependences of the 19F NMR T1F of the CF2Cl and CF3 groups lead to activation energies of 13 and 4.3 kJ mol-1 , respectively, for the same reorientations. T1F of the CF3 group observed above ca. 200 K was attributed to the spin-rotational interaction. The T1Q
-1 of ring-chlorine in 4 - ClC 6H4NHCOCCl3 and 4 - ClC6H4NHCOCF3 can be interpreted by the Tn law with n = 2.2 and 1.1, respectively, whereas that of 4-ClC6H4NHCOCF2Cl by the sum of two contributions: Tn law (n = 2.0) and the modulation mechanism due to the CF2Cl reorientation
Anomalous Temperature Dependence of the 99Tc Quadrupole Coupling and Disordering of Cesium Positions in CsTcO4
Authors: Tarasov V. P. , Kirakosyan G. A. , German K. E. 
Published: February 2015

Abstract
A 99T c and 133Cs solid-state NMR study of polycrystalline CsTcO4 at a field of 7.04 T and temperatures from 90 to 430 K revealed first-order quadrupole effects. 99T c quadrupole coupling constant, C
q
, shows anomalous positive temperature coefficients and decreases from 2.0 MHz at 430 K to 0.45 MHz at 90 K. The asymmetry parameter, η (99Tc) , is zero at 430 K and at 210 K. The high-temperature minimum of η is associated with a phase transition from orthorhombic to tetragonal and the second minimum reflects an orientational change of the principal axes qxx and qyy of the EFG-tensor.
The 133Cs NMR spectra are characterised by a superposition of the two powder multiplets from the first-order couplings which arise from magnetically and crystallographically nonequivalent cesium sites, Cs (1) and Cs (2); the population ratio of Cs (2) and Cs (1), p2/p1 , varies from 2.0 at 120 K to 6.5 at 373 K. The nonequivalence and population changes are attributed to the temperature change of the crystal field potential in the vicinity of the cations.
35Cl NQR and Molecular Motion in Solid C6X5Cl (X = H, F)
Authors: Gordeev A. D. , Soifer G. B. , Zhukov A. P. 
Published: February 2015

Abstract
The 35Cl NQR frequency and spin-lattice relaxation time of solid chlorobenzene and chloropentafluorobenzene at temperatures from 77 K to the melting points have been measured and explained by thermoactivated librations and reorientations of the molecules around the normal to their plane. The activation energies of these motions have been estimated
2 D Methods in NQR Spectroscopy
Authors: Seliger J. , Blinc R. 
Published: February 2015

Abstract
The application of two-dimensional spectroscopy to nuclear quadrupole resonance (NQR) is reviewed with special emphasys on spin 3/2 nuclei. A new two-dimensional level crossing double resonance NQR nutation technique based on magnetic field cycling is described. This technique allows for a determination of both the electric quadrupole coupling constant and the asymmetry parameter for spin 3/2 nuclei in powdered samples even in cases where the quadrupolar signals are too weak to be observed directly. It works if the usual double resonance conditions are met, i.e. if the spin-lattice relaxation times are not too short if the quadrupolar nuclei are dipolarly coupled to "strong" nuclei. Variations of this techique can be also used for 2 D "exchange" NQR spectroscopy and NQR imaging.
Contribution of Microwave Fourier Transform Spectroscopy to the Investigation of Nuclear Quadrupole Coupling
Authors: Dreizler Helmut 
Published: February 2015

Abstract
By simple examples it is shown how fine structures in rotational spectra of free molecules can be used to analyse nuclear quadrupole coupling. It is demonstrated that microwave Fourier transform spectroscopy is an adequate tool for these studies. Examples for different nuclei illustrate the present possibilities