The anomalous temperature dependence of NQR frequencies which is often observed in crystals in which there is reorientational motion of ions or molecules is considered. Two theories of the phenomena, the jump rotation theory and the pseudo-spin theory, are described, and their successes and failures are discussed. The importance of considering other properties such as pressure dependence of NQR...

A reinvestigation of the nitrogen-14 NQR in thiourea has permitted to record, apparently for the first time, the resonances above 169 K. The first order and second order of the transitions at 169 K and 202 K, respectively, appear clearly from the temperature dependence of the resonance frequencies; the modulated structure, incommensurate or commensurate, is also seen on the N NQR spectrum. This...

The performance of rectangular radio frequency (RF) coils capable of being used to detect nuclear quadrupole resonance (NQR) signals from blister packs of medicines has been compared. The performance of a fixed-pitch RF coil was compared with that from two variable-pitch coils, one based on a design in the literature and the other optimized to obtain the most homogeneous RF field over the whole...

A very high sensitivity continuous wave NQR spectrometer was developed to detect pure NQR transitions at low frequencies (down to 200 kHz). A signal-to-noise ratio of more than 100 to 1 has been achieved at about 1.36 MHz for crystalline B 2 0 3 . Two large n B responses have been found in vitreous B 2 0 3 (NMR detected only one site) with linewidths of less than 30 kHz. A1 NQR spectra were obt...

The 1 2 7 I-NQR of(HOCH 2 )3 CNH 3 I was determined in the range 77 < T/K<310. At T = 310 K the NQR signal fades out (Tm = 463 K). The 127I spectrum ( T =77 K.): v, =29.195 MHz, v2 = 14.597 MHz, rj(121l)=0, e Q # zz6 _ 1 (1 2 7 I) = 97.315 MHz, is in agreement with the crystal structure. The 127I NQR spectrum of l,3-diammonium-2,2-dimethylpropane diiodide, (H 3 NCH 2 C(CH 3 ) 2 CH 2 N H 3)2+ -2...

We performed $^{59}$Co nuclear magnetic and quadrupole resonance (NMR NQR) measurements under pressure on a single-crystalline CeCoSi, which undergoes an unresolved phase transition at $T_0$. The NQR spectra clearly showed that the $T_0$ is nonmagnetic, but any symmetry lowering Co site was not seen irrespective of feature second-order transition. By contrast, NMR were split by induced field pe...

The results of comparison of experimental C1 NQR parameters for a great number of organic and organometallic compounds and estimated ones using ab initio calculations at the RHF/6-31G(d) level were systematized. The NQR frequency changes on going from one compound to another depend, in general, on the changes of populations of the CI atom p„-orbitals in these compounds and, first of all, of pop...

Stable crystalline 2-chlorothiophene has two glass transitions at 164 and 186 K. CI NQR measurements were carried out between 77 and 200 K. Two NQR signals with full widths of about 100 kHz at half maximum were observed in this temperature range. The spin-lattice relaxation times Ti were measured at the two peak frequencies. The activation energy obtained from the results of the T\ measurements...

The influence of the cations on the condensation of the anions in the salts (A')Zn(II) Br4 and (A)2Zn(II)Br4 is studied by 81 Br NQR and X-ray crystal structure analysis. (A')Zn(II)Br4(A' = [H3N(CH2)3NH3] + ) (1) shows a phase transition at 474 K. The phase II of (1) crystallizes with isolated [ZnBrJ " tetrahedra: monoclinic P2 t/«, Z = 4, a = 1108.4 (5), b = 1096.8 (2), c = 1118.5 (6) pm, and ...

The local bonding structure in the Ge–As–Se ternary glassy system has been investigated by As nuclear quadrupole resonance (NQR) at 77 K. For the compositions with average coordination number r 1⁄4 2:2; 2:4; 2:54 the NQR measurements yield no evidence for the presence of As–As homopolar bonds. For the composition Ge2As2Se5 ( r 1⁄4 2:67) the NQR lineshape exhibits two peaks corresponding to arse...