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1992[X]
21Author    Sundara Ramaprabhu, EdwinA C LückenRequires cookie*
 Title    Cu and 79 81 Br NQR Studies of Thione Complexes of Cu(I) Halides  
 Abstract    63, 65£ U NQR frequencies, together with their temperature dependence, are reported for several complexes formed between cuprous chloride or bromide and heterocyclic thiones. For bromides the 79,8fgr 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. 
  Reference    Z. Naturforsch. 47a, 125—128 (1992); received July 26 1991 
  Published    1992 
  Keywords    NQR, Copper(I), Thione 
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 Identifier    ZNA-1992-47a-0125 
 Volume    47 
22Author    A. Sasane, T. Matsuda, H. Honda, Y. MoriRequires cookie*
 Title    Bromine-79 NQR for uncoordinated Br ions in fraw5-[CoBr2(en)2][H 5 0 2 ]Br2  
 Abstract    A single 79 Br NQR line showing a frequency of 19.594 MHz at room temperature has been observed in the crystals of trans-[CoBr2(en)2] [H502]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 [H502] + 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. Key words: 79 Br NQR frequency, Br" ion, hydrogen bonding, electric field gradient (EFG), Stern-heimer effect. 
  Reference    Z. Naturforsch. 47a, 129—133 (1992); received July 18 1991 
  Published    1992 
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 Identifier    ZNA-1992-47a-0129 
 Volume    47 
23Author    E. A. Kravchenko, M. Yu, BurtzevRequires cookie*
 Title    Electron Effects of Adduct Formation by some Metal Halides  
 Abstract    The results of NQR studies on electron density redistribution due to formation of adducts of various types of metal halides are reviewed and their consistency with X-ray data is discussed. 
  Reference    Z. Naturforsch. 47a, 134—140 (1992); received July 21 1991 
  Published    1992 
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 Identifier    ZNA-1992-47a-0134 
 Volume    47 
24Author    ValentinP. FeshinRequires cookie*
 Title    NQR Studies of Organic Compounds Containing Tetra-or Pentacoordinated Atoms of Elements of Groups IVA and VIA  
 Abstract    The 35 C1 and 79 Br NQR spectra of halogen-containing organic compounds of Si, Ge, Sn and Te, in which these atoms may be tetra-or pentacoordinated, have been compared to the results of their X-ray diffraction analysis. The NQR technique was also used to study a large number of such compounds for which X-ray investigations were found to be impossible. It has been shown that the NQR technique may be considered as a rapid method for the determination of the electronic and spatial structure of these compounds. The conditions for pentacoordination of atoms of IVA group elements have been also formulated. 
  Reference    Z. Naturforsch. 47a, 141—146 (1992); received June 29 1991 
  Published    1992 
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 Identifier    ZNA-1992-47a-0141 
 Volume    47 
25Author    MikhailG. Voronkov, GennadiiV. Dolgushin, ValentinP. Feshin, LyudmilaP. Turchaninova, NikolaiA. Korchevin, EleonoraN. DeryaghinaRequires cookie*
 Title    C1 NQR Spectra of Organyl(chloroalkyl) Sulfides  
 Abstract    The 35 C1 NQR spectra of organyl(chloroalkyl) sulfides C1CH2S(CH2)"CH3, « = 0-11, Cl(CH2)mSR, m = l-3 and alkyl(chloromethyl selenides ClCH2SeR (R = C2H5, C3H7) have been obtained. In going from m = 1 to m = 2, the electron density on the CI atom in the series Cl(CH2)mYR increases when Y = S and decreases when Y = O. 
  Reference    Z. Naturforsch. 47a, 147—149 (1992); received December 16 1991 
  Published    1992 
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 Identifier    ZNA-1992-47a-0147 
 Volume    47 
26Author    ValentinP. Feshin, GelenaA. Polygalova, VasiliiV. Shchepin, YuriiE. SapozhnikovRequires cookie*
 Title    Spatial Electron Density Distribution of Chlorine Atoms in Molecules of the Series C1 2 C = CXX  
 Abstract    The EFG asymmetry parameters at 35 C1 nuclei have been measured for polycrystalline com-pounds of series C12C = CHX (X = OR, OCOR) and Cl2C = C(Cl)OCOR at 77 K. For the Cl trans-atoms in molecules C12C = CHX, the q values are equal or close to zero. For the Cl cis-atom of these compounds and for all Cl atoms of compounds Cl2C = C(Cl)OCOR, r/ ~6-9%. It was shown that the deviation from the axial symmetry of electron distribution of Cl atoms in these compounds is due to the influence not of the geminal, but of a vicinal atom or group directly through the field. The expected p, ^-conjugation between the unshared electron pair of halogen and the Ti-electron system of double bond is absent in the molecules studied. 
  Reference    Z. Naturforsch. 47a, 150—152 (1992); received June 29 1991 
  Published    1992 
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 Identifier    ZNA-1992-47a-0150 
 Volume    47 
27Author    G. Wulfsberg, K. Shadid, B. Farris, J. Monn, T. Bonner, J. Yanisch, Al WeissRequires cookie*
 Title    Dioxin Precursors: NQR Studies of Group 1 and Related 2,6-Dichlorophenolate and 2,4,6-Trichlorophenolate Salts  
 Abstract    The 81 Br and 35 C1 NQR spectra of anhydrous Group 1, tetraalkylammonium, and thallium(I) 2,6-dichlorophenolates, 2,4,6-trichlorophenolates, and 4-bromo-2,6-dichlorophenolates were searched for evidence of solid-state cation-organochlorine interactions that might, for example, be (in part) responsible for the difference in the thermal decomposition reactions of these salts (to give the supertoxic environmental pollutants, the polychlorinated dibenzodioxins) versus those of the corresponding Group 11 chlorophenolate complexes, which do not decompose to dioxins. For cations ranging in size from tetraethylammonium to potassium, the total range of 35 C1 NQR frequencies in 2,6-dichlorophenolate and 2,4,6-trichlorophenolate salts is only 1.401 MHz, which, although larger than the 0.7 MHz range likely in molecular chlorocarbons, is smaller than in individual chlorophenolates of copper(I) and silver(I) (up to 2.0 MHz). In sodium and thallium(I) 2,4,6-trichlorophenolates substantially large frequency shifts (ca. 2.0 MHz) occur, to higher frequen-cies for the para-chlorines and lower frequencies for the ortho-chlorines (Na only). These disappear even in closely related compounds and show a pattern that seems unrelated to the decomposition products of the chlorophenolates. 
  Reference    Z. Naturforsch. 47a, 153—159 (1992); received July 16 1991 
  Published    1992 
  Keywords    Chlorophenolates, Nuclear quadrupole resonance, Dioxin 
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 Identifier    ZNA-1992-47a-0153 
 Volume    47 
28Author    Dirk Groke, Shi-Qi Dou, Alarich WeissRequires cookie*
 Title    CI NQR and Structural Studies of Chloroacetanilides C 6 H 3 C1 2 NHCOCH 3 _ x C1 ;C , 1 < jc<3  
 Abstract    The temperature dependence of 35 C1 NQR frequencies and the phase transition behaviour of chloroacetanilides (N-[2,6-dichlorophenyl]-2-chloroacetamide, -2,2-dichloroacetamide, -2,2,2-tri-chloroacetamide) were investigated. The crystal structure determination of N-[2,6-dichlorophenyl]-2-chloroacetamide leads to the following: a = 1893.8 pm, £> = 1110.7 pm, c = 472.1 pm, space group P212121 = D2 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-dichloro-phenyl]-acetamide. For N-[2,6-diclorophenyl]-2,2,2-trichloroacetamide it was found: a = 1016.6 pm, 6 = 1194.3 pm, c= 1006.7 pm, ß= 101.79°, space group P21/c = C^h, Z = 4. The structure is similar to the low temperature phase of N-[2,6-dichlorophenyl]-acetamide. Parallelism between the temper-ature dependence of the 35 C1 NQR lines of the CC13 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 35 C1 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 35 C1 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 temper-ature phase and an instable high temperature phase (at room temperature) were observed. The different phases were detected by means of 35 C1 NQR spectroscopy and thermal analysis. 
  Reference    Z. Naturforsch. 47a, 160—170 (1992); received August 8 1991 
  Published    1992 
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 Identifier    ZNA-1992-47a-0160 
 Volume    47 
29Author    Morteza Shabazi, Shi-Qi Dou, Alarich WeissRequires cookie*
 Title    Br and 127 1 NQR of tert-Butylammonium Halides and Crystal Structure of (CH 3 ) 3 CNHf Br e  
 Abstract    The 79 Br and the 127 I NQR spectrum of tert-butylammonium bromide and iodide, respectively, was studied as a function of temperature. No phase transition was observed for the bromide in the temperature range covered. The 79 Br NQR frequency is 9.056 MHz at 113 K and increases with increasing temperature (10.040 MHz at 293 K). The NQR spectrum reveals a phase transition of (CH3)3CNHfI e around 360 K with pronounced hysteresis. The nuclear quadrupole coupling constant of 127 I is 69.335 MHz with an asymmetry parameter of 0.154 for the high temperature phase at T = 370 K. For the low temperature phase the corresponding values are 67.136 MHz and 0.081 at 300 K. The crystal structure of tert-butylammonium bromide was studied at room temperature. The compound crystallizes orthorhombic, space group D^jj-Pbca, with 4 formula units in the unit cell, a = 1832.1 pm, 6 = 918.5 pm, c = 899.8 pm. The crystal structure and hydrogen bond system are discussed in connection with the NQR results. 
  Reference    Z. Naturforsch. 47a, 171—176 (1992); received June 25 1991 
  Published    1992 
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 Identifier    ZNA-1992-47a-0171 
 Volume    47 
30Author    Shi-Qi Dou, Alarich WeissRequires cookie*
 Title    NQR and Crystal Structure of 4,5-Dichloroimidazole, C 3 H 2 N 2 C1 2  
 Abstract    The two line 35 C1 NQR spectrum of 4,5-dichloroimidazole was measured in the temperature range 77^ T/K ^389. The temperature dependence of the NQR frequencies conforms with the Bayer model and no phase transition is indicated in the curves v(35 Cl)= f(T). Also the temperature coefficients of the 35 C1 NQR frequencies are "normal". At 77 K the 35 C1 NQR frequencies are 37.409 MHz and 36.172 MHz and at 389 K 35.758 MHz and 34.565 MHz. The compound crystallizes at room temperature with the tetragonal space group D4-P41212, Z = 8 molecules per unit cell; at 295 K: a = 684.2(5) pm, c = 2414.0(20) pm. The relations between the crystal structure and the NQR spectrum are discussed. 
  Reference    Z. Naturforsch. 47a, 177—181 (1992); received June 14 1991 
  Published    1992 
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 Identifier    ZNA-1992-47a-0177 
 Volume    47 
31Author    G. Frantz, R. Leiberich, P. C. Schmidt, T. P. DasRequires cookie*
 Title    Theoretical Study of the Electric Field Gradient in Silver Iodide  
 Abstract    The electric field gradient (EFG) in hexagonal Agl at the iodine site is studied theoretically by three different procedures, namely the point charge model, the Hartree-Fock cluster approach, and the augmented plane wave band structure procedure. A comparison is made for the electronic charge distribution and the sizes of the various contributions to the EFG obtained by the different proce-dures. From the point charge model and the Hartree-Fock cluster approach one gets almost the same result for the EFG, q = +0.743 • 10 21 V/m 2 and +0.816 • 10 21 V/m 2 respectively. Only a rather preliminary result of q = +0.393 • 10 21 V/m 2 is found by the band structure calculation to be compared with the experimental value of q exp = ±0.415 • 10 21 V/m 2 . The confidence limits of the theoretical results are discussed, including possible ways to bridge the gap between the theoretical results by different methods and experiment. Both the cluster and the band structure calculations are shown to support an ionic model for hexagonal Agl with some overlap between the charge distributions on neighboring ions. 
  Reference    Z. Naturforsch. 47a, 182—188 (1992); received October 25 1991 
  Published    1992 
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 Identifier    ZNA-1992-47a-0182 
 Volume    47 
32Author    Pekka PyykköRequires cookie*
 Title    The Nuclear Quadrupole Moments of the 20 First Elements: High-Precision Calculations on Atoms and Small Molecules  
 Abstract    The available values of the nuclear quadrupole moments for the elements H -Ca are reviewed and related to recent advances in numerical methods in quantum chemistry. For Li the quantum chemical and nuclear Coulomb scattering values now agree. For Mg, also the muonic result agrees with them. For Na and Al, the new, accurate atomic values deviate from the earlier muonic values. 
  Reference    Z. Naturforsch. 47a, 189—196 (1992); received July 27 1991 
  Published    1992 
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 Identifier    ZNA-1992-47a-0189 
 Volume    47 
33Author    Karlheinz Schwarz, Peter BlahaRequires cookie*
 Title    Ab initio Calculations of the Electric Field Gradients in Solids in Relation to the Charge Distribution  
 Abstract    A first principles method for the computation of electric field gradients (EFGs) is illustrated for various solids. This scheme is based on self-consistent energy band-structure calculations by the full potential linearized augmented plan wave (FLAPW) method which provides the electronic charge density including all polarization effects. By numerically solving Poisson's equation we obtain the Coulomb potential in a form which allows to compute the EFG directly. Our method is demon-strated for insulators (Cu20), metals (hcp-Zn), supercondutors (YBa2Cu3Ö7) and molecular crystals (Cl2, Br2, I2). 
  Reference    Z. Naturforsch. 47a, 197—202 (1992); received August 3 1991 
  Published    1992 
  Keywords    Band-structure calculation, Electric field gradient, Nuclear quadrupole interaction, Molecular crystals, High-Tc superconductors 
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 Identifier    ZNA-1992-47a-0197 
 Volume    47 
34Author    MichaelH. PalmerRequires cookie*
 Title    The ab initio Calculation of Nuclear Quadrupole Coupling Constants with Special Reference to 33 S  
 Abstract    The ab initio calculation of 33 S nuclear quadrupole coupling constants (NQCC) for a range of S-containing compounds with S 2 , S 4 and S 6 bonding types is described. All of the calculations used a triple zeta valence + polarisation basis set (TZVP) of gaussian type orbitals; all of the molecules were studied at the TZVP equilibrium geometry. The electric field gradients (EFG) calculated were correlated with the experimental NQCC obtained by either microwave spectroscopy (MW), nuclear quadrupole resonance (NQR) or NMR relaxation methods; although the experimental data cover a wide diversity of chemical types over a long period of time, the slope of the relationship between the EFG (q u) and the NQCC (x u) yields a value for the 33 S atomic quadrupole moment of — 0.064 barn, very close to recent calculations with a large atomic basis set, and to experimental data. The relationship between the EFG tensor components and the internal molecular structure features is discussed for a diverse series of molecules. 
  Reference    Z. Naturforsch. 47a, 203—216 (1992); received August 20 1991 
  Published    1992 
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 Identifier    ZNA-1992-47a-0203 
 Volume    47 
35Author    Juan Murgich, Yosslen Aray, EdgarOspina RicoRequires cookie*
 Title    N NQR and the Molecular Charge Topology in Coordinated Ammonia  
 Abstract    14 N NQR spectra of [Co(NH3)6] • 3C1, [Co(NH3)5C03] • N03, [Zn(NH3)4] • 2C1, [Zn(NH3)4] • (BF4)2, and [Ag(NH3)4] • N03 were obtained at 77 K. The results, analyzed by means of the topology of the charge distribution obtained from ab-initio MO calculations of free and of a model of coordinated NH3, showed that bonding to the metal-ion produces a strong decrease (Co^>Zn %Ag) in the N nonbonded density ("lone pair") and an increase in the bonded maxima found in the N-H bond direction of the N valence shell. 
  Reference    Z. Naturforsch. 47a, 217—220 (1992); received August 3 1991 
  Published    1992 
  Keywords    14 N NQR, Ammonia, Complex, Charge distribution, Topology 
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 Identifier    ZNA-1992-47a-0217 
 Volume    47 
36Author    RobinL. Armstrong, Sunyu SuRequires cookie*
 Title    Milli-Kelvin NQR: A Study of the Praseodymium Trihalides  
 Abstract    Milli-Kelvin NQR experiments are often essential for the study of pseudo one-dimensional materials. A brief overview of the special technical consideration for carrying out NQR measure-ments in a dilution refrigerator is given. Recent halide quadrupole resonance experiments on the pseudo one-dimensional XY crystals PrCl3 and PrBr3 are reviewed including the measurement and interpretation of frequencies, and spin-lattice relaxation times. 
  Reference    Z. Naturforsch. 47a, 221—226 (1992); received August 8 1991 
  Published    1992 
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 Identifier    ZNA-1992-47a-0221 
 Volume    47 
37Author    HaeJin Kim, KeeTae Han, SungHo ChohRequires cookie*
 Title    Electric Field Effect on 14 N NQR in Ferroelectric Thiourea Single Crystals ** *  
 Abstract    The electric field effect on 14 N 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, dvj h /d£+ = 0.87±0.10, dvx + /d£_ = 1.17±0.20, dv2 + /d£+ = 0.80±0.10, and dv2 + /d£_ = 0.90 ±0.15. These values are on the order of 10 2 times those found in other ferroelectric crystals such as sodium nitrite (NaN02). The remarkable difference between these two Stark shifts is discussed by taking into account the polarizability and the local electric field at the 14 N sites in these crystals. 
  Reference    Z. Naturforsch. 47a, 227—231 (1992); received August 4 1991 
  Published    1992 
  Keywords    Electric field effect, Stark shift, 14 N NQR, Ferroelectric thiourea, Thiourea single crystal 
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 Identifier    ZNA-1992-47a-0227 
 Volume    47 
38Author    Hirokazu Nakayama, Taro Eguchi, Michihiko KishitaRequires cookie*
 Title    Phase Transitions in Bis(4-chlorophenyl)sulfone as Studied by 35 C1 FT-NQR  
 Abstract    The temperature dependence of 35 C1 NQR frequencies in bis(4-chlorophenyl)sulfone was mea-sured in the temperature range of 4.2-297 K. Below 115 K four NQR lines due to four inequivalent chlorines exist in the commensurate phase, contrary to the single NQR line reported by Corbero et al. It follows that the commensurate-incommensurate transition is of the first-order, and the incommensurate-normal transition at 150 K is quasi-continuous. It is also suggested that the succes-sive phase transitions are triggered by the small angle rotation of the molecules about their C2-axes. 
  Reference    Z. Naturforsch. 47a, 232—236 (1992); received July 10 1991 
  Published    1992 
  Keywords    35 C1 NQR, Bis(4-chlorophenyl)sulfone, 'H NMR, Incommensurate phase, Phase tran-sition 
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 Identifier    ZNA-1992-47a-0232 
 Volume    47 
39Author    F. Milia, G. Papavassiliou, A. AnagnostopoulosRequires cookie*
 Title    NQR Study of the Pinning and Depinning of the Incommensurate Modulation Wave in the Presence of Impurities  
 Abstract    High temperature-resolution NQR measurements in an ultra pure Rb2ZnCl4 crystal and a mixed [Rb[ _x(NH4)J2ZnCl4 crystal with a controlled amount of impurities (x = 0.01) verify the existence of a temperature region where the characteristic incommensurate line splitting is averaged out. The results show that for the system with high purity the averaging of the incommensurate splitting is due to large thermal fluctuations. In contrast, for the mixed crystal the added impurities seem to play the predominant role. 
  Reference    Z. Naturforsch. 47a, 237—240 (1992); received December 2 1991 
  Published    1992 
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 Identifier    ZNA-1992-47a-0237 
 Volume    47 
40Author    Reha Basaran, Shi-Qi Dou, Alarich WeissRequires cookie*
 Title    C1 NQR and Crystal Structure Studies of Salts of Chlorodifluoro-and Dichloroacetic Acid  
 Abstract    The 35 C1 NQR spectra of several chlorodifluoroacetates were studied as a function of tempera-ture, including the acid ClF2CCOOH. The cations were: Ammonium, guanidinium, paramethyl-anilinium. Also some acid salts M®ClF2CCOO e • n-ClF2CCOOH (n>l) were studied by 35 C1 NQR. The bleaching temperatures of the NQR signals were determined. In the para-methyl-anilinium salt and in the guanidinium salt a phase transition has been observed. The crystal structure of guanidinium chlorodifluoroacetate has been determined at room temperature (a = 1089 pm, 6 = 845 pm, c = 832 pm, space group Pnma, Z = 4). For comparison, guanidinium dichloroacetate was studied by 35 C1 NQR and by X-ray diffraction, too: P2i/c, Z=4, a = 804pm, 6 = 1202 pm, c= 1080 pm, ß = 131.58°. For guanidinium chlorodifluoroacetate and chlorodifluoroacetic acid, the 35 C1 spin lattice relaxation time Tt and the line width have been followed up as a function of temperature. Therefrom, the activation energies of the reorientation motion of the group -CF2C1 have been determined to be 14 kJ • mol" 1 (from Tj) and 12.5 kJ • mol" 1 (from A\) for the pure acid and 9.2 kJ • mol" 1 and 8.8 kJ • mol" 1 , respectively, for the guanidinium salt. 
  Reference    Z. Naturforsch. 47a, 241—250 (1992); received July 11 1991 
  Published    1992 
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 Identifier    ZNA-1992-47a-0241 
 Volume    47 
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