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The nature of the smectic Ad to nematic phase transition and the modes of molecular motion were investigated for the homologous mesogens, CBOOA, NBOOA, and their chain-deuteriated compounds. In NBOOA, the SA d[sbnd]N phase transition was found to be first order with a pronounced pretransitional decrease of the orientational order parameter, , both above and below the transition point, while in CBOOA the anomaly in was very small. Despite the different behaviours in terms of the orientational order, the dynamical aspects of molecular motion, probed by the-NMR relaxation, are quite similar. The motional mode characteristic of the N phase is order director fluctuation, but translational self-diffusion becomes the dominant relaxation mechanism in the SA d phase. It is also recognized that the relative importance of these mechanisms changes in a continuous manner as a function of temperature.

Proton spin-lattice relaxation rates were measured in Zeeman and dipolar fields in the liquid crystalline phases (N–S Ad –RN) of OBBC, 4-(4''-octyloxybenzoyloxy)-benzylidene-4'-cyanoaniline. The relaxation mechanisms were analyzed from the frequency- and temperature-dependences of the relaxation rates. The Zeeman relaxation mechanism in the high temperature nemanic (N) phase was characterized by the long-range fluctuation of the nematic director, whereas in the reentrant nematic (RN) phase the relaxation was predominated by translational self-diffusion of molecules. On the other hand, the relaxation in the dipolar frame caused by director fluctuation was observed in all of the three liquid crystalline phases. It is suggested that persistence of nematic director fluctuation in the smectic Ad mesophase is related to the reentrance phenomenon in polar mesogens.

Proton T1D and T1 ρ are measured on ammonium sulfate crystal with 0.8% and 7.3% 17O content, at 30 and 10 MHz. A marked reduction is observed in T1D and T1 ρ compared with normal specimens at temperatures above about 200 K. At 30 MHz, T1D showed a minimum at about 240 K while two minima were observed for T1 ρ in the similar temperature range. Both T1D and T1 ρ at 10 MHz showed different behaviors from those measured at 30 MHz. These experimental results are interpreted in terms of H–O dipole modulation by the SO2−4 reorientation and by the fluctuation of the z component of 17O spin due to strong quadrupole relaxation. From the temperature dependence of the relaxation times, an activation energy of 21 kJ mol−1 and a preexponential factor of 3×10−11 s are obtained for the correlation time of the SO2−4 ion reorientation in the paraelectric phase. The correlation time exhibited a discontinuous change at Tc. Anomalous temperature dependence of the correlation time is observed in the ferroelectric phase. This b...

The pure quadrupole resonance spectra were observed on Cl 35 and Cl 37 in BCl 3 and Br 79 and B 81 in BBr 3 at several temperatures. The spectrum of each nucleus consists of characteristic doublet (ν I and ν II ) with the intensity ratio of ca. 3 to 5. The Zeeman study with a single crystal of BBr 3 was also carried out at liquid nitrogen temperature (77°K), to determine the asymmetry parameter η. The results are as follows

Deuteron magnetic resonance (DMR) of single crystals of Cu(DCOO) 2 ·4D 2 O has been studied from 153°K to 291°K to reveal the changes in the structure and the motions of the crystalline water molecules due to the paraelectric-antiferroelectric phase transition ( T c =246.1±0.2°K). Above T c , all the DMR lines of water molecules are broadened out by fast motions of deuterons among seven sites. Below T c , 20 pairs of DMR lines are observed corresponding to four water molecules in stable position and two formate ions and their a c -plane enantiomorphs. Following conclusions are derived from measurements of temperature and angular dependences of the quadrupole splittings for these DMR lines. The phase transition is an order-disordering type of water molecules. In the antiferroelectric phase, the unit cell doubling occurs along the c -axis direction and the space group is P 2 1 / n . The structure involves a three dimensional ordering of water molecules. The structure of hydrogen-bond network is determined. ...

Quadrupole splitting of deuteron magnetic resonance was measured for a single crystal of Ba(ClO3)2·D2O. Quadrupole coupling, asymmetry parameter, and principal axis directions of the field gradient tensor were determined at 20° and at —130°C. eqQ/h=121.5±0.4 kc/sec, η=0.976±0.007 at 20°C, and eqQ/h=243.5±1.5 kc/sec, η=0.074±0.002 at —130°C. The field gradient at room temperature shows a rapid reorientation of the water molecule in a crystal. At room temperature, the spectral line exhibits fine structure due to coupling of two spins, which was utilized to determine the sign of eqQ in the present case.The line broadening effect in the intermediate temperature region (—45°∼—121°C) was measured and was used to obtain the reorientation rate at various temperatures. The barrier to reorientation of 6.6 kcal/mole was obtained from the comparison of the experimentally determined reorientation rate with that calculated from a tunneling process through a hindering barrier, or that of 6.5 kcal/mole from classical pro...

A study on the Zeeman effect of Cl 35 nuclear quadrupole resonance spectrum was carried out on a single crystal of cyanuryl chloride. Three distinct q -tensors were found in this crystal, two of them being equivalent. The directions of the principal axes were determined within the accuracy of 1° . It was concluded that in the crystal all molecules are disposed parallel (or antiparallel) to one another and three C–Cl bonds of a molecule are on a plane, making an angle 120° with one another, one of them being not equivalent to the other two. A large asymmetry parameter, 0.26, was obtained. From the coupling constant and the asymmetry parameter, the double bond character and the ionic character of C–Cl bonds were estimated to be 10% and 17%, respectively. The large double bond character was considered to be associated with the large electronegativity of nitrogen atoms in the ring.

Deuteron magnetic resonance study is made of single crystals of LiD 3 (SeO 3 ) 2 between -143°C and 110°C. The electric quadrupole coupling constant, e Q q / h , the asymmetry parameter, η, and the directions of the principal axes of the field-gradient tensor are determined for each deuteron at room temperature. Three non-equivalent tensors are obtained corresponding to the three non-equivalent fairly strong hydrogen bonds determined by X-ray diffraction. The e Q q / h and η are 107.8 kc/sec and 0.172 for D a , 127.9 kc/sec and 0.154 for D b , and 181.1 kc/sec and 0.101 for D c , The hydrogen-bond network in LiD 3 (SeO 3 ) 2 is determined. The atomic coordinates of deuterons are estimated from the results of the present DMR study. The field-gradient tensor of 7 Li is also determined at room temperature. The values of e Q q / h and η are 33.9 kc/sec and 0.593.

Deuteron and 23 Na magnetic resonances are measured of single crystals of NaD 3 (SeO 3 ) 2 between 134°K and 298°K to reveal the nature of the ferroelectric transition ( T c ∼267°K). Deuteron resonance lines D a and D b (relative intensity 1:2) above T c split into two and into four, respectively. The 23 Na resonance line above T c also splits into two below T c . Following conclusions are derived from measurements of temperature and angular dependences of the quadrupole splittings for these deuteron and 23 Na resonance lines. All the hydrogen atoms are linked with moderately strong hydrogen bonds, and are jumping back and forth in the double well potential above T c . The phase transition is accompanied not only by order-disordering of hydrogen atoms in hydrogen bonds, but also by slight rotations of SeO 3 - ions and by a slight distortion of lattice in the neighborhood of Na + ions. The crystalline symmetry below T c is monoclinic, and the cell-doubling occurs along the b axis. Hydrogen-bond network bel...

四塩化炭素を開始剤に用い,三塩化チタンートリエタノールアミンにより-10℃ 前後の温度で重合したポリ塩化ビニル(PVC)の広幅およびパルスNMRを行ない市販品と比較した。試料は常法で精製し市販品は減圧乾燥して用いた。低い温度で重合したPVCの広幅スペクトルはある温度範囲で二つに分れる。吸収の広い部分がポリエチレンのように結晶に基くとすれぽ,動的結晶度は30～40%になり,110℃ 以下でその幅は変らないが,これを超えると運動は急に開放される。ポリエチレングリコールを加えて乳化重合したものには,50℃ 以上で鋭い吸収が現われ,これを精製しても消えない。スピン格子緩和の機構は簡単でなく,緩和時間(T1)は二つ以上含まれる。T1の温度依存性から分子運動を考察した。-196℃ で広幅スペクトルの吸収幅はどのPVCも期待される値よりやや大きく,塩素核による核四重極効果が考えられる。